DINOSAURS of UTAH Frank Decourten Dinosaurs of Utah

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Second Edition DINOSAURS OF UTAH Frank DeCourten Dinosaurs of Utah

Second Edition

Frank DeCourten

The Defiance House Man colophon is a registered trademark of the University of Utah Press. It is based on a four-foot-tall Ancient Puebloan pictograph (late PIII) near Glen Canyon, Utah.

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Library of Congress Cataloging-in-Publication Data DeCourten, Frank. Dinosaurs of Utah / Frank DeCourten. — Second Edition. pages cm Includes bibliographical references and index. ISBN 978-1-60781-264-7 (pbk. : alk. paper) — ISBN 978-1-60781-265-4 (ebook) 1. Dinosaurs—Utah. I. Title. QE862.D5D42 2013 567.909792—dc23 2013006059

Printed and bound in Korea. Contents

Preface vi

01. The Mesozoic World: The Earth in Upheaval 1

02. Dawn of the Utah Mesozoic: The Age of Dinosaurs Begins 23

03. The Early and Middle Jurassic: A Time of Transition 46

04. The Late Jurassic: The Golden Age of the Sauropods 75

05. Blood Brothers: The Predators of the Morrison Formation 120

06. The Early Cretaceous: The (Un)Missing Links 143

07. The Late Cretaceous: The Beasts of the Bayous 172

08. The Curtain Falls: The Dinosaurs of the North Horn Formation 210

09. Doing It: The Allure of Paleontology 234

Appendix: Classification of Dinosaurs 243

References 255

Index 283 Utah’s Dinosaur Record. Graphic developed by the Utah Geological Survey, available online at: http://geology.utah.gov/utahgeo/dinofossil/index.htm. Preface

For a science that embraces an immense time strengthened their staffing, and emphasized paleon- dimension, twelve years can be a long time in pale- tology in their educational programs and outreach ontology. It was about that long after the publication activities. Examples include the Utah Natural His- of the first edition of Dinosaurs of Utah that Peter tory Museum operated by the University of Utah, DeLafosse initially suggested updating that book the Prehistoric Museum at the Utah State Univer- into the edition you are now reading. Peter’s sug- sity–Eastern campus, and Dixie State College. These gestion was prompted by his perception that a great public investments in preserving and investigat- deal of new information on Utah dinosaurs had sur- ing Utah’s fabulous paleontological resources have faced over the past decade and a half, and a new edi- had a dramatic impact. More paleontologists prob- tion was needed to incorporate the results of recent ably reside and work in Utah now than at any time advances in knowledge. He couldn’t have been more in the past. correct; it is only a slight exaggeration to declare Two important developments at the federal level that we have probably learned as much about Utah have helped to stimulate paleontological investi- dinosaurs over the past twenty years or so as was gations since the original edition of this book was learned during the preceding century. The surge published. In 1996 the Grand Staircase–Escalante of new discoveries about Utah dinosaurs and the National Monument was established in the magnif- world that they inhabited has been nothing short of icent landscapes of southwest Utah. The state lands explosive. Many new species of dinosaurs have been within the monument were consolidated in 1998, identified, their patterns of distribution and evolu- and today more than 1.9 million acres are set aside tion have been established and interpreted, and new for the benefit of future generations. Part of the analytical techniques have been applied to fossils management plan for the new monument entailed to formulate neoteric reconstructions of dinosaur a detailed survey of the paleontological resources anatomy and physiology. of the region, which includes extensive tracts of What stimulated the current renaissance in Utah remote land with difficult access. These surveys dinosaur paleontology? A number of factors have included rock exposures that had not been exam- contributed to the current wave of exciting research ined carefully for fossils. Many significant discover- in paleontology in the state. First, Utah is one of ies of dinosaur fossils were made by the monument only a handful of states that maintain an Office of scientists and their university and museum col- the State Paleontologist (Dr. James Kirkland), which leagues who conducted the surveys in this large is a part of the Utah Geological Survey. This office parcel of magnificent land. In addition, subse- was created in the late 1970s and has since become quent management plans have strongly supported of pivotal importance in encouraging, coordinating, the ongoing scientific studies of the fossils that and facilitating paleontological research in Utah. have been excavated from federal lands within the In addition, over the past two decades a number of monument. Also, the United States Paleontologi- Utah public institutions have significantly improved cal Resources Protection Act was passed and signed their facilities for paleontological research, into law in 2009. This legislation strengthened the

vii viii Preface legal protection of vertebrate fossils on federal land in particular were gracious in sharing new informa- and provided for the care and preservation of fos- tion on Utah dinosaurs and fossil localities. Several sils for the public good. Federal agencies such as the individuals from the U.S. Bureau of Land Manage- Bureau of Land Management have carried out this ment also were very helpful in providing informa- legal mandate and, in the process, made strong con- tion on the status of paleontological work being tributions to the advancement of knowledge in ver- carried out on the lands under their jurisdiction. tebrate paleontology in Utah. The Utah Geological Survey has been a valuable The general public has also played a signifi- source of information for this book and contributed cant role in the recent progress of dinosaur paleon- several of the graphics contained herein. Some of tology in Utah. Utah Friends of Paleontology has the original dinosaur art by Carel Brest van Kempen grown from a small nascent organization in 1998 to is used again in this book. I am grateful for Carel’s a strong statewide network of trained amateur pale- talent and gift for creating such spectacular images ontologists who have made several significant fossil of nature, past and present. Dr. Ronald Blakey, discoveries and helped professional paleontolo- president of Colorado Plateau Geosystems, Inc., gists conduct their excavations and research pro- generously permitted the use of his excellent recon- grams. Along with the many individuals associated structions of ancient landscapes. Peter DeLafosse of with Utah’s public and private institutions, Utah the University of Utah Press, in addition to suggest- Friends of Paleontology has helped ignite the recent ing a second edition, was consistently supportive explosion in dinosaur studies by providing an army and patient during the long and often delayed pro- of dedicated dinosaur enthusiasts. The extraordi- cess of revision. My old partner Tom Hill provided nary level of public support of paleontology in Utah support and sustenance during our fieldwork for the today is unduplicated at any other time since the project, as he has continuously for several decades first dinosaur bones were discovered in the state of romping about together on the back roads of more than one hundred years ago. Utah. All of these developments would render any The overall goal of this book is the same as in 1998 compilation of information on Utah dinosaurs the original edition: to tell the story of Utah’s dino- somewhat dated. This is certainly the case with the saurs against the backdrop of changing Mesozoic first edition of Dinosaurs of Utah. Accordingly, the landscapes and ecosystems. Of course, we will never current edition is an attempt to update the content know all the details of that story: our knowledge of the original by incorporating the many advances of both the dinosaurs and the world they inhab- in our knowledge of Utah dinosaurs made over ited is still fragmentary and incomplete, regard- the past two decades. Such work, like paleontology less of how much we’ve learned in the recent past. itself, is always a collaborative effort. I have bene- It is almost certain that some of the enduring mys- fited enormously from correspondence and discus- teries that this book identifies will be closer to res- sions with many people in the process of compiling olution by the time it makes its way into the hands all the new information included in this book. Many of any reader. No end of the Utah dinosaur renais- of my scientific colleagues contributed to this effort. sance that began in the 1980s is in sight: it appears Dr. Ken Carpenter of the USU–Eastern Prehistoric that we can look forward to an indefinite future of Museum, Dr. Alan Titus of the Grand Staircase– captivating new discoveries. Whatever is learned in Escalante National Monument, Dr. Randy Irmis the future will enrich our understanding of one of of the Natural History Museum of Utah, and Scott the most fascinating periods in Utah’s deep natural Williams of the Burpee Museum of Natural History legacy, the Mesozoic era. However incomplete our Preface ix current knowledge is, the story of Utah’s dinosaurs reconstructing this story will help us understand the is nonetheless an extraordinary tale of life evolv- rapidly changing world that we have inherited from ing to changing conditions for more than 180 mil- the dinosaurs and craft a way to continue evolving lion years. I hope that the lessons we learn from in harmony with the planet we inhabit. 1.1. The Mummy Cliffs near Capitol Reef National Park. Courtesy John Telford.

1.2. This butte near Hanksville is capped by hard Mesozoic sandstone, while the badlands of the lower slopes are eroded from soft shale. Courtesy John Telford. Chapter 1 The Mesozoic World The Earth in Upheaval 01 Anyone familiar with the rugged landforms of Utah encompassing hundreds of millions of years and sooner or later begins to take cliffs for granted. Ver- reducing the “ancient” Egyptian mummies to mere tical walls of rock stand everywhere in this elevated youngsters. land of mountains, buttes, mesas, and plateaus. The Mummy Cliffs continue east toward Capi- From the edges of the high tablelands, steep slopes tol Reef, where they become folded down into the commonly cascade down to meet the adjacent low- subsurface as younger rock layers are draped over lands with magnificent abruptness. We never lose the Waterpocket Fold. Eventually the bold cliffs our awareness of the cliffs around us, like the walls of sandstone open to the east to reveal a color- of the rooms in our home, but their distinctive ful panorama of badlands, ledges, buttes, and pla- aspects seem to fade namelessly into the surround- teaus beyond the mouth of the Fremont River. The ing grandeur. Even their spectacular beauty eventu- scenery is astonishing in this area. On any summer ally becomes so commonplace that we accept them morning the shoulders of Highway 24 are crowded as just another adornment in an exquisite landscape. with the cars of tourists photographing the amaz- It is easy to understand, then, why so many ing vistas. As visually impressive as this landscape people traveling east through central Utah tend to is to most people, it produces a special thrill for overlook a relatively modest red bluff north of State the paleontologist. The red ledges, pastel badlands, Highway 24, east of Torrey. These great stone sen- gray hummocks, and sandstone buttes (fig. 1.2) are tinels standing guard over the entrance to Capi- the trademark of the Mesozoic era, the great age of tol Reef National Park are called the Mummy Cliffs dinosaurs. Just the sight of them brings a flutter to (fig. 1.1). It’s a good name, too, for the castellated the heart of anyone interested in ancient reptiles. red bluffs project countless fluted columns that look The Mummy Cliffs are the gateway to the Mesozoic for all the world like the linen-wrapped remains of wonderland of eastern Utah. ancient Egyptian royalty. The rusty pillars emerge Eastern Utah, from the Four Corners region from the cliff with ragged outlines, their surfaces north to the Uinta Basin, is a natural museum of streaked with black desert varnish and separated the Mesozoic that has attracted paleontologists to from each other by shadowy clefts. Standing ver- the area for well over a hundred years. The rock lay- tically along the highway, they watch the stream ers exposed across this bold landscape are mostly of vehicles pass with an eerie humanlike counte- of Mesozoic age, from 245 to about 65 million years nance. Their narrow bases broaden upward into a old. In places, most notably in the deeper canyons of fluted “body,” often capped by a stony “head.” Even the Colorado River system, older rocks are exposed the most casual observer will sense that these Utah beneath the cover of red-hued Mesozoic strata. mummies are relics of the past, representing former Likewise, on the highest surfaces of eastern Utah’s times and former worlds. Few, however, will readily plateaus and mesas, younger rocks overlie the dino- comprehend the immensity of the history that these saur-bearing layers. But over thousands of square rocks record. That history is unfathomably deep, miles between the canyon floors and the highest rim

1 2 Chapter 1 rocks, on the broad expanses that seem to sweep MESOZOIC from horizon to horizon, the rocky Mesozoic record CRETACEOUS PERIOD lies exposed, waiting to be explored. And what a curious world awaits those who investigate the 145 M.Y. rocks behind the scenery!

JURASSIC PERIOD Mesozoic Mayhem: Life and Land in Turmoil

The Mesozoic is one of three great eras of geo- ERA 201 M.Y. logic time, spanning more than 180 million years between the Paleozoic (542–251 million years ago) TRIASSIC PERIOD and the Cenozoic (65 million years ago to the present). As these epithets suggest, each era is named 251 M.Y. for the type of life, recorded as fossils in the rocks, 1.3. The Mesozoic era. Because of uncertainties in the that dominated the successive phases of our planet’s methods of absolute dating, the dates of the various subdivisions are approximate to within about 5 percent immense history. It was the British geologist John of their actual values. Phillips who in 1840 first suggested the term “Meso- zoic” for the era of “middle life.” As envisioned by Phillips, the Mesozoic encompassed (from oldest to youngest) the Triassic, the Jurassic, and the Cre- taceous (fig. 1.3). These periods had been established by geologists in other places at other times, but they were all defined on the basis of characteristic and recurring assemblages of fossils. The fossils from the three Mesozoic periods were much different from those of the preceding Paleozoic or the following Cenozoic and seemed to constitute a unique and distinctive stage in the evolution of life. But how was the life of the Mesozoic unique? Let us approach that question first with a brief review of the life of the preceding (Paleozoic) era and following (Cenozoic) one. The Paleozoic was the time of “ancient life.” Rocks of this age produce the remains of many primitive organisms such as trilobites, grapto- lites, crinoids, brachiopods, corals, and primitive armored fish, to name just a few (fig. 1.4). Though some of these groups persist today, the Paleo- zoic organisms all appear very strange and primitive in comparison with their living descendants. 1.4. Some common Paleozoic fossils of Utah: A. Lithostrotian, a Mississippian coral; B. Bathyurellus, an Many of the Paleozoic organisms are now extinct Ordovician trilobite; C. Anthracospirifer, a Pennsylva- and/or are so bizarre that questions still linger con- nian brachiopod; D. Faberophyllum, a Mississippian sol- cerning their proper classification and relationships itary coral; E. Syringopora, a Silurian coral. The Mesozoic World 3

fossils are for the most part similar to living creatures and can usually be classified with ease (fig. 1.5). Between the peculiar Paleozoic forms and the much more familiar Cenozoic organisms are the Mesozoic fossils, remains of creatures from the era of “middle life.” Many Mesozoic fossils are tran- sitional between the “primitive” and “modern” types, as we might expect, but not all are. Among the Mesozoic fauna are scores of animals that are uniquely bizarre, bearing little resemblance to anything that preceded or followed them. This is because the Mesozoic era was a time of evolutionary experimentation that followed two notable events in the history of the earth’s biosphere: a massive extinction and the fragmentation of a supercontinent. Both of these events exerted a profound effect on the patterns of evolution and extinction that are recorded by the fossils of Mesozoic age. In the long history of life on our planet, the combination of such circumstances was unique to this era. The animals of the Mesozoic were more than simply “tran- sitional”; collectively they represent a unique stage in the history of life when rapidly changing condi- 1.5. Some common Utah Cenozoic fossils: A. Viviparus, a Paleocene gastropod (snail); B. a Pliocene horse tooth; tions led to an evolutionary frenzy that produced an C. Aralia, an Eocene angiosperm leaf. amazingly varied menagerie of creatures on land, in the seas, and in the skies. with modern groups. The Cenozoic, which follows the Mesozoic, is known as the great “Age of Mam- Life of the Mesozoic mals,” for this class of organisms came to dominate the world’s terrestrial ecosystems during the last 65 At the end of the Paleozoic, at the close of the Perm- million years. In some ways the designation “Age ian period about 250 million years ago, a great wave of Mammals” is unfortunate, because the Cenozoic of extinction swept the world. The primary vic- was also a time of rapid evolution among plants, tims of this late Paleozoic event were marine inver- insects, fish, reptiles, and microscopic organisms of tebrates, such as the trilobites and other primitive all sorts. The mammals were certainly not the only organisms mentioned above. It has been estimated group to experience explosive evolution during the that up to 95 percent of the species living in the Cenozoic. But we belong to this group, so I suppose shallow seas near the end of the Paleozoic vanished that we have the prerogative (or the arrogance) to during the extinction event. The seafloor communi- call it “our time.” Nonetheless, the Cenozoic is defi- ties of reef-building corals and bryozoans, clamlike nitely the age of “modern” life; few Cenozoic fossils brachiopods, and trilobites and other arthropods present the same problems of classification and rela- were devastated during the Permian extinctions, tionships that we see so commonly among the more with many of the species in these groups disappear- bizarre Paleozoic forms. These relatively young ing forever. 4 Chapter 1

The effects of the extinction on land are more instantaneous global distribution during the time difficult to assess because the fossil record is not when other terrestrial vertebrates were so drastically so rich, but we do know that many groups of ter- declining. The great extinction was followed by one restrial plants and animals died out. The primitive of the most dramatic pulses of evolution ever: the ferns and scaly-barked trees of the great Paleozoic explosion of the reptiles. Though the pattern and coal swamps began to decline and were ultimately timing of this evolutionary outburst was far from replaced by the conifers that dominated the Meso- simple, the overall effect was to transform the ter- zoic forests. Some three-fourths of the species of restrial fauna to a reptile-dominated assemblage by land animals that existed at the end of the Paleozoic the early Mesozoic. We will return to the reptilian era did not survive into the Mesozoic. The princi- “takeover” in chapter 2, but first let’s complete our pal terrestrial victims of the extinctions were primi- overview of the Mesozoic world. tive mammal-like reptiles, insects, and amphibians. No one knows with absolute certainty what The amphibians had developed from lobe-finned caused the great late Paleozoic extinction (called fish some 100 million years before the extinction, the Permo-Triassic extinction for the two periods of during the Carboniferous period. They had become geologic time between which it occurred, the Perm- remarkably abundant on land as the Paleozoic came ian and the Triassic). Many scenarios have been to a close. Many giant amphibians lived during this proposed as a cause for this event, ranging from time, some up to 20 feet (7 meters) long. Among shifting continents to abrupt climate change, to oxy- them were fierce alligatorlike predators and large gen-depleted seas, to asteroid impacts. In reality browsing plant eaters. The small and relatively rare the Permo-Triassic event was the greatest biotic cri- amphibians of today—frogs, toads, and salaman- sis in earth history and probably resulted from sev- ders—represent only a depauperate relict of the eral factors that produced a near-collapse of the gaudy late Paleozoic assemblage. As the end of the global ecosystem. While it is beyond our scope fully Paleozoic approached, the great amphibians began to explore the complexities and controversies of the to die out, along with some large mammal-like rep- Permo-Triassic event, one thing is certain: when tiles known as synapsids. the Mesozoic began, the survivors of the extinc- As many of the large vertebrate creatures of the tion nearly everywhere in the world were freed from Permian vanished, they left ecological niches vacant much of the competition that their ancestors had in the swamps and forests that they formerly inhab- faced for millions of years. In response the land-liv- ited. The Permian extinction thus created great evo- ing reptiles started a collective riot of evolution that lutionary opportunities for any organisms that was to last for more than 150 million years, until the could survive the crisis and develop successful adap- next biotic calamity. In the process some of the most tations to the rapidly changing environment. One peculiar creatures ever to inhabit our planet devel- such group of survivors that weathered the extinc- oped as new body designs were formulated, tested, tion storm to inherit the major niches during the abandoned, and modified through natural selection. Mesozoic, of course, was the small reptiles. Having Mesozoic life was rich and diverse but also a little developed an externally laid (amniote) egg tens of strange, due to the unique pace of evolution and millions of years prior to the extinction, the reptiles the presence of many “evolutionary experiments.” could not have been in a better position to replace This is why scientists regard the Mesozoic as much the amphibians and synapsids as the dominant ver- more than a simple transition from “primitive” life tebrates of the global ecosystem. With a reproduc- to “modern” life; it was a time of previously unpar- tive system that allowed broad dispersal into dry alleled evolutionary innovation among the reptiles habitats, the relatively small reptiles achieved almost and, as we shall see, other groups as well. The Mesozoic World 5

1.6. Mesozoic ammonites from Utah: A. Cadoceras, middle Jurassic; B. Clioscaphites vermiformis, late Cretaceous; C. Scaphites warreni, late Creta- ceous. Bar = 0.4 inch (1 cm) in all sketches.

On land, in the sea, and in the air the major eco- wheels). Meanwhile other types of molluscs, such as logical niches filled by large animals were dom- clams (bivalves) and snails (gastropods), burrowed inated by reptiles after the Paleozoic ended. through the muddy sediments on the seafloor, Accordingly, the Mesozoic is referred to as the Age where they competed with starfish, sea urchins, of Reptiles. Dinosaurs represent just the tip of the and a horde of crustaceans. Some of the gastro- iceberg of Mesozoic reptilian dominance: the flying pods evolved carnivorous habits, feeding on other and gliding pterosaurs, the marine ichthyosaurs and bottom-living invertebrates, becoming the “killer plesiosaurs, the aquatic and semiaquatic turtles and snails” of the day. Many of the prey organisms living crocodiles, and the many kinds of snakes and lizards on the seafloor developed antipredation adaptations complete the saurian menagerie that overshadowed such as thickened shells, swimming abilities, or con- other vertebrate groups everywhere in the world. cealment strategies (burrowing or protective color- Along with the reptilian congregation were some ation). Overall the invertebrate fauna populating the very peculiar nonreptiles. Muted beneath the ongo- Mesozoic seafloor was a well-adapted, mobile, and ing reptilian riot, some very significant evolutionary highly specialized aggregate that replaced the more events also took place in other animal groups. sessile and generalized Paleozoic assemblage. For most of the Mesozoic era the forests of the Fish prospered during most of the Mesozoic, world were dominated by relatively primitive plants including the peculiar lobe-finned coelacanths such as gigantic ferns and the cone-bearing gymno- thought to be extinct until the accidental discovery sperms (conifers, cycads, ginkgoes, and so forth). of a living species in 1938 in the deep waters offshore The more advanced flowering plants (angiosperms) from Madagascar. In the Mesozoic oceans other arose near the end of the Mesozoic and have now bony fish specialized in the predation of bottom-liv- replaced the less specialized gymnosperms as the ing invertebrates. Many of these sturgeonlike fish had major component of the modern global flora. In “pavements” of shell-crushing teeth and must have the oceans the entire marine ecosystem was over- been voracious bottom feeders. Swim-bladders devel- turned and reshaped following the Permo-Trias- oped in fish for the first time later in the Mesozoic, sic extinction. Microscopic plankton such as the giving rise to swift and agile swimmers well adapted diatoms, coccolithophores, and other tiny organ- to pursue active prey. More kinds of sharks, Paleozoic isms exploded onto the scene during the Mesozoic, “holdovers,” were probably around in the Mesozoic replacing the more primitive and less varied Paleo- than today. Finally, in freshwater environments, lung- zoic forms. The coiled ammonites (fig. 1.6), rela- fish and heavily scaled relatives of the modern gar tives of the modern pearly nautilus, swarmed in were particularly abundant in lakes and rivers. incredible abundance and achieved gigantic pro- The mammals were few in number and types portions (some species grew as large as wagon throughout most of the Mesozoic, but they were 6 Chapter 1

equipped to step out from the shadows of the Meso- zoic world. Birds arose from dinosaurian ancestors in the early Mesozoic and fluttered (originally with toothed beaks and clawed wings) alongside the pterosaurs through the skies above the Mesozoic jungles and plains. Toss in a few enormous marine crocodiles, the manateelike placodonts, the giant aquatic lizards known as mosasaurs, and the seagoing plesiosaurs and ichthyosaurs and you can see that it was a strange bestiary indeed that ruled the Mesozoic world (fig. 1.7).

Mesozoic Land and Geography

The strangeness of Mesozoic life, particularly in comparison to our own late Cenozoic flora and fauna, was mirrored in the inanimate earth as well. If we could revisit a Mesozoic landscape, the conditions around us would seem every bit as exotic as the plants and animals that we would observe. Moreover, the Mesozoic was a time of constant and 1.7. Strange creatures of the Mesozoic era, excluding dinosaurs. A. a rudist bivalve (clam) that mimics the sometimes rapid change in geography, climate, and form of the Paleozoic solitary corals; B. Stenopteryg- geological activity. The dinosaurs evolved against ius, a lower Jurassic ichthyosaur; C. Quetzalcoatylus, the backdrop of continuous and profound change a gigantic pterosaur with a wingspan of up to 50 feet; D. the skull of Phobosuchus, a “fearsome crocodile” in the earth environment. Before we examine the exceeding 45 feet in length; E. the lower jaw of Styg- details of Utah’s Mesozoic landscapes and habitats, mius, a small rodentlike Cretaceous mammal; F. Cynog- let’s explore some of the global factors that helped nathus, a mammal-like reptile from the Triassic period. shape them. We know that the global geography of the Meso- present in the undergrowth, in the limbs of the zoic was much different from the world we know trees, and in ground nests. The dinosaurs and their today. At the beginning of the era a single enormous reptilian kin relegated them to the world’s ecolog- supercontinent known as Pangaea existed. Assem- ical backwaters for over 140 million years. Rat- bled from smaller fragments that collided during like in appearance, nearly all of the mammals of the Paleozoic, Pangaea stretched nearly from pole to the Mesozoic were small creatures, probably weigh- pole as an unbroken block of land surrounded by a ing only a few ounces (see Foster 2009 in refer- global ocean, the Panthalassa. The east-central mar- ences for chapter 4). Sometime during the Mesozoic gin of Pangaea was incised around a large embay- the tiny mammals nonetheless managed to develop ment known as the Tethys Sea, creating a narrow the reproductive and physiological advantages that “neck” in the supercontinent about where it strad- serve as the foundation for their dominance in the dled the equator (fig. 1.8). The pattern of oceanic cir- modern world. Once the dinosaurs disappeared (or culation and the global climate were both affected by did they?—see chapter 8), the mammals were well the location and size of Pangaea (as we’ll soon see). The Mesozoic World 7

About 35 million years after the beginning of the Mesozoic Pangaea started to break apart. The rifting was initiated in the Tethys region and penetrated to the west until the great supercontinent had been severed into two large fragments north and south of the equator. The northern portion is known as Laurasia (consisting of the ancient cores of North America, Eurasia, and Greenland); south of the equator was Gondwana (composed of South Amer- ica, Africa, Antarctica, Australia, and India prior to their individual separation). The two fragments, each much larger than any modern continent, moved slowly apart at a rate of a few centimeters (an inch or so) per year (fig. 1.8). Near the end of the Mesozoic the two fragments of Pangaea themselves eventually broke apart into the smaller continents that we are accustomed to in our world. Some of the small fragments later collided with each other, reversing the trend of continental fragmentation that started at the dawn of the Mesozoic. For example, North America bumped into the corner of Asia near the end of the Mesozoic, while India began its ongoing collision with the southern border of Asia just after the Mesozoic ended. Thus the geography of the Mesozoic world was continually changing, following a pattern of generally increasing continental isolation punctuated by occasional rejoining. This unique aspect of the Mesozoic world had a powerful effect on the patterns of dispersal, evolution, and extinction for all life, including the dinosaurs. When all the land on earth was united and connected in the early Meso- zoic, there were few barriers to the dispersal and migration of terrestrial organisms. Under such conditions, communities of the land-living animals became widespread. The fossils preserved on continents now separated by great distances show strong similarity. Later in the Mesozoic increasing continental isolation led to the development of some unique or endemic faunas on some continents. The reversal of this trend, a general decline in endemism of the dinosaurs and other creatures, would occur 1.8. Continental configurations of the Mesozoic era. whenever previously separated continental masses Adapted from Sereno 1991. 8 Chapter 1 were joined. The effect of changing global geogra- oceanic circulation. This continuous rearrange- phy is clearly seen in some of the patterns of dino- ment of land and sea affected the climates all over saur dispersal and evolution in Utah. This will be the world. In general, though with some exceptions, an important consideration for us in later sections the global climate became less seasonal and less where we examine the distribution and relationships variable toward the end of the Mesozoic. Scientists of specific dinosaurs. In any case the rapid pace of have inferred from the study of temperature-sen- evolution of Mesozoic life can be explained at least sitive isotopes in oceanic sediments that the over- in part by the adaptation of organisms to the contin- all climate was at least 10°C (18°F) warmer in later uously shifting environmental conditions brought Mesozoic time than it is today, and there may have about by changes in global geography. been times of extreme global warming driven primarily by volcanic activity (more on this later). The temperature difference between the tropics and the The Mesozoic Climate polar regions was also much weaker in the Meso- Reconstructing ancient climates is not a simple zoic, particularly during the Cretaceous period, enterprise. Scientists have developed ways to esti- than today. mate aspects of climate such as the mean global temperature, carbon dioxide levels in the prehistoric The Mesozoic Seas atmosphere, and Mesozoic precipitation patterns. This is done primarily by integrating studies of car- The Mesozoic seas were as different from the mod- bon and oxygen isotopes in Mesozoic sediments, ern oceans as dinosaurs are from living lizards. mapping the distribution of certain climate-sensi- Recall that in the early Mesozoic a single global tive deposits such as salt layers, and interpreting the ocean known as the Panthalassa surrounded Pan- moisture requirements of preserved plant fossils by gaea. With the early fragmentation of Pangaea in analogy with living relatives. Such integrated mod- the Mesozoic, water from this ocean flooded into els of the Mesozoic climate can reveal the broader the newly created basins of the Atlantic, Pacific, global patterns but cannot provide detailed recon- and Indian Oceans. The global ocean of the Meso- structions of climate on a local scale. Nonethe- zoic likely contained more water than today’s ocean less, reconstructions of the overall character of the does, because permanent polar ice did not exist Mesozoic climate are reasonably consistent, despite on earth during much of the Mesozoic. Today the the continuing uncertainties about specific local world’s ice caps and glaciers contain a little more conditions. than 2 percent of the world’s water. If this ice were to Post-Pangaean climates appear to have been a melt, sea level would rise by some 250 feet. At times complex collage of warm and moist conditions in the Mesozoic sea level actually stood much higher the narrow equatorial regions, temperate condi- than this because the capacity of the ocean basins tions farther north and south, and searing inte- was reduced by geological processes (see the next rior deserts. Drier environments such as semiarid section). By late Mesozoic time (the Cretaceous) sea steppes and true deserts seem to have been more level was 300 feet higher than in the modern oceans widespread in the early Mesozoic than they are (Müller and others 2008) but also subject to the sig- today. In addition, we have no evidence that the nificant fluctuations over time (Miller and others earth possessed any appreciable ice caps during this 2003). time. As Pangaea began to break apart, new ocean Consequently the low coastal plains and inte- basins developed between the diverging continen- rior basins on every continent were repeatedly sub- tal masses, which changed the pattern of global merged as the bloated oceans rose and crept inland The Mesozoic World 9 during the Cretaceous. The advancing oceans bacteria and other microbes. Modern seafloor mud would pause or even recede during the times when contains some carbon, but in most places it is not sea level fell in response to ocean basin dynam- rich enough in organic material to develop a black ics, only to resume their invasion of dry land when color. The prevalence of black shale in the Mesozoic sea level rose again. This stutter-step, on again–off suggests either that the population of decomposing again invasion of the shallow seas over continen- organisms on the seafloor was minimal or that the tal margins started about 100 million years ago and rate of organic production in the planktonic realm eventually submerged low-lying portions of every was unusually high. continent in the world. At the time of maximum It is likely that both factors contributed to the inundation in the late Cretaceous, North America abnormally widespread black shale of the Mesozoic. was separated into two “island” continents as the The warmth of the Mesozoic, probably enhanced by ancient Gulf of Mexico advanced north through the the high concentrations of atmospheric CO2 near central plains to meet the water creeping south from the end of the era, would have produced a “bloom” the Arctic region. The western margin of the inte- of plankton in the seas. The warm global climate rior seaway ran north and south through central would have created the marine equivalent of a year- Utah (see chapter 7). Similar flooding of continental round growing season for millions of years. The lowlands occurred simultaneously on all other con- increased amount of carbon dioxide in the late tinents. The advances and withdrawals of seas over Mesozoic atmosphere might have acted like plant continental lowlands had a significant influence fertilizer, leading to a great proliferation of pho- on the pattern of dinosaur evolution because the tosynthetic phytoplankton. Whatever decompos- amount and character of the dinosaur habitat would ing organisms lived on the ocean floor at that time shift with each invasion and retreat of the oceans. no doubt experienced a deluge, rather than a gentle Another oddity of Utah’s Cretaceous rocks seems rain, of organic matter from above. to reflect the unusual global climatic conditions At the same time the global warmth would have and oceanic circulation of the Cretaceous. All over slowed down or even sporadically eliminated the the world the mud that accumulated on the sea- circulation of water in the deeper ocean basins. This floor during the late Mesozoic is characteristically is likely because the cold, dense seawater from the rich in carbon. The fine sediment commonly con- frigid polar regions in today’s oceans sinks, contin- tains so much carbon that the resulting rock exhib- uously displacing the less dense and warmer bottom its a dark gray or black color. Geologists have coined water of the abyssal plains. These sinking cold water the term “black shale” to describe such rocks. Black masses drive the entire cycle of top-to-bottom oce- shales are particularly widespread during the Cre- anic circulation. In the warm Mesozoic, without the taceous period and are represented in Utah by rock cold polar conditions, the polar bottom waters may units such as the Mancos Shale and Tropic Shale have become warm and stagnant (Huber and others (fig. 1.2) that typically form striking barren badlands 2002), depleted in the oxygen and nutrients (Pucéat in eastern and southern Utah. Most of the carbon 2008) necessary to sustain large populations of scav- in these deposits originated as the organic residue engers and decomposing microbes. Thus even the from planktonic organisms floating near the sur- deepest sea floor environments seem to have been face of the sea. When these organisms died, their affected by the disarray of the Mesozoic world. remains descended toward the seafloor as a more or Interestingly, even though the black shales of less constant rain of organic, carbon-rich matter. On Utah accumulated under the shallow seas that today’s seafloor this organic material is consumed encroached over the central part of North America, by mud-feeding organisms and/or decomposed by they do contain some significant dinosaur fossils. 10 Chapter 1

Though it may seem that deep ocean environments In the middle part of the Cretaceous the recur- have little to do with land-living dinosaurs, we rent shifting of the magnetic polarity stopped dead will encounter this connection in chapters 6 and 7. in its tracks. About 120 million years ago the mag- But first we need to consider even more Mesozoic netic field shifted to normal polarity from reversed strangeness. and stayed that way for at least 35 million years. What happened? Did the currents in the outer core stagnate? Did the inner regions of the earth “over- Mesozoic Convulsions in the Deep Earth heat” so that rocks below the surface lost their During the last 50 or 60 million years of the Meso- magnetic properties? No one knows. But the long zoic era something happened inside the earth as “normal epoch” in the late Mesozoic is a unique well. We have good evidence that the normal cir- event in earth history. It may be that this period culation of the molten iron deep within the earth, of stability (or stagnation?) of the interior earth is in the zone known as the outer core, became stag- related to some of the other peculiar aspects of the nant or otherwise disrupted late in the Mesozoic. Mesozoic world as described below. The timing is The evidence comes from studies of paleomagne- certainly suspicious, for some other very strange tism: the investigation of the magnetic properties things begin to happen on the earth precisely when of ancient rocks. By examining the paleomagnetic the magnetic field stops reversing polarity. character of rocks of varying ages, geologists have During the Cretaceous, in part overlapping the been able to identify literally hundreds of times period of magnetic stagnation, great volumes of since the end of the Paleozoic when the polarity of molten rock (magma) were erupted or emplaced the earth’s magnetic field reversed itself. The rea- beneath the surface in many places around the sons for the periodic reversals of magnetic polar- globe. In fact geologists consider the late Meso- ity remain obscure; but the magnetic field is thought zoic to be the most intense period of igneous activ- to be produced by the circulation of iron in the ity since life originated on our planet. More igneous outer core coupled with the earth’s rotation, so geo- rock formed on the surface (volcanic rocks) and physicists speculate that the pattern, rate, or direc- underground (as plutonic rocks, like granite) in the tion of interior circulation may shift from time to Cretaceous than during any other period of geo- time, causing the polarity to “flip.” We do know that logic time. In North America the granitic rocks the reversals are a normal part of the earth’s inte- of the Sierra Nevada in California, the Coastal rior rhythms, with at least 170 oscillations over the Range of British Columbia, the mountains of cen- past 75 million years or so. We have no evidence of tral Idaho, and rugged peaks of the Baja Califor- great extinctions or other natural disasters associ- nia peninsula are entirely of Mesozoic age, mostly ated with the magnetic reversals. The reversals seem Cretaceous. Elsewhere, on the floor of the western to occur rapidly (geologically speaking), requiring Pacific Ocean basin, millions of cubic kilometers of only a few thousand years to develop. The reversals lava poured out to build the Ontong-Java Plateau occur in a more or less random pattern, at an aver- about 120 million years ago (Taylor 2006). Molten age interval of about a half-million years in the rel- rock also surged into the great oceanic ridges at this atively recent geologic past. It is interesting to note same time, increasing the rate of seafloor spreading that we have been in a period of “normal” polar- in the late Mesozoic Era to as much as 5 inches/year, ity for about 780,000 years, so we’re due for a rever- more than three times the average rate today (Lar- sal at any time. We may understand the process and son 1991). Great masses of lava also flooded onto consequence of the reversals better if (or when) we the land surface in places like India and Pakistan, have the opportunity to live through one. where more than 2,400 cubic miles of volcanic rock The Mesozoic World 11 formed the Deccan traps near the end of the Creta- form in the deep sea ooze (Jahren 2002). During the ceous. This outburst of igneous activity in the late Mesozoic CO2 and other gases from the widespread Mesozoic world, a time when all hell broke loose and intense eruptions must have accumulated in the throughout the globe, occurs during the great mag- atmosphere, producing a “super greenhouse” effect netic stagnation. and raising the global temperature by least 10°C.

Though we do not yet understand exactly how Geologists have estimated that CO2 concentrations this torrent of rising liquid is linked to the sus- in the Cretaceous atmosphere may have oscillated pected disruption of circulation in the deep outer between 600 and 2,400 parts per million (ppm), core, it almost certainly is. It may be that the nor- compared to the modern value of about 390 ppm mal heat-dissipating currents (whatever their form (Bice and others 2006). Geochemical evidence from may be) decayed and the mantle “overheated” dur- oceanic sediments suggests that by the Cretaceous ing the late Mesozoic. In response to the extreme deep seawater near the poles had become at least heating, immense pockets of the semisolid material 25°C warmer than in today’s oceans (Huber and melted and gushed upward as great plumes of mol- others 2002). The volcano-induced warmth likely ten rock into the oceanic ridges, increasing the rate prevented the formation of permanent ice caps and of seafloor spreading and plate motion. Elsewhere produced a searing climate, for at least the last por- on the seafloor, huge masses of this rising fluid tion of the Mesozoic. erupted to form the great lava plateaus and extensive chains of undersea volcanoes. As the rate of Cosmic Chaos seafloor spreading increased, older oceanic materials were pushed down under continents at an accel- The final element of ecological disarray in the Meso- erating pace. Known as subduction, this process zoic comes at the very end, about 65 million years results in the production of even more molten rock ago at the close of the Cretaceous period. We have (magma) at depth. The great igneous outburst of very good evidence that some type of extraordi- the Cretaceous may reflect the generation of many narily explosive event or events occurred. On a scale large plumes of hot material that migrated upward that appears to be almost global, sediment depos- from the overheated core toward the outer crust. ited at this time has produced concentrations of ele- Many geologists refer to these ascending columns ments such as iridium that are extremely rare on as the “superplumes” of the late Mesozoic, and they the earth’s surface but significantly more abundant are thought to be linked to both the intense igneous in asteroids and meteorites. In addition, geologists activity of the time and the simultaneous accelera- have discovered in these same deposits unusu- tion in the fragmentation of Pangaea (Vaughan and ally “shocked” mineral grains, peculiar micro- Story 2007). scopic globs of carbon that appear to be the “soot” The great igneous outburst no doubt had a strong of global wildfires and tiny spheres of glassy mate- effect on the global environment of the late Meso- rial. The origin of these oddities stimulated con- zoic. When volcanoes erupt, they liberate enormous siderable debate among geologists in the 1980s and quantities of gas along with the lava that flows from 1990s, and several different hypotheses were devel- them. Steam (water vapor), carbon dioxide (CO2), oped to explain the strange aspects of the late Cre- sulfurous gases (H2S, SO2), and other noxious efflu- taceous rock record. We will explore this issue in vium emanate as towering plumes above the sum- more detail later, but there is a strong consensus mits of erupting volcanoes. Lava erupting on the among geologists today that the strange character of seafloor can also liberate methane (CH4), a power- latest Cretaceous rocks is due to the impact between ful greenhouse gas, from the frozen clathrates that the earth and a large extraterrestrial object, probably 12 Chapter 1 an asteroid. Thus nearly all geologists agree that the the size, shape, and arrangement of grains in a sand- Mesozoic went out with a bang—a fitting end to a stone, we might be able to ascertain whether the convulsive phase in the history of our planet. We sand accumulated in a dune, as a sandbar in a river, will return to the events and the conditions that or along the beach of some ancient lake or sea. In accompanied the end of the Mesozoic in chapter 8. a similar manner, features of conglomerates such In summary, the dinosaurs were not the only as the orientation of the pebbles, their style of lay- extraordinary aspect of nature in the Mesozoic. ering, and their size and composition can allow In contrast to the familiar patterns and natural geologists to determine the size and type of river rhythms of today, the entire era was a time of the that deposited them, the direction of flow, and the peculiar, the bizarre, and the extreme. Whenever we likely source of the rock particles. If we examine contemplate the dinosaurs from the perspective of the characteristics of many sedimentary rock lay- life in our own Cenozoic era, we should remember ers that formed at the same time over a broad area, that they inhabited a world that was very different it becomes feasible to reconstruct the major features from our own. of the landscape at the time the grains were deposited. Such reconstructions of ancient environments and landscapes are important in the study of any The Nature of the Mesozoic Rock Record of Utah group of organisms (including dinosaurs) whose Rocks formed during the Mesozoic are widespread remains might be preserved in the rock as fossils. in Utah, particularly in the Colorado Plateau prov- This is because the complete understanding of any ince of the eastern and southern portions of the prehistoric animal requires some knowledge of the state. Mesozoic rocks are exposed over more than environment in which it lived. Fortunately, the sed- 25,000 square miles statewide, including the majes- imentary rocks that produce Utah’s dinosaur fos- tic landscapes of red rock canyons, pastel-col- sils often contain a wealth of clues about the local ored badlands, and imposing cliffs in eastern Utah. environment as well. Whenever dinosaur bones These rocks are dominantly sedimentary, consist- are discovered, paleontologists carefully excavate ing of mineral grains of various sizes that accumu- the fossils and meticulously record information on lated in lakes, riverbeds, dunes, and floodplains of the nature of the enclosing rock and associated fos- ancient Utah. Over the millions of years since their sils. Without all the associated data, fossils can only deposition the grains have become compacted and tell us part of the story. We are left in that case with cemented into layers of solid stone. Sandy grains many frustrating questions that cannot be answered. .002–0.08 inch in size have become sandstone, This is one reason why dinosaur excavations often while accumulations of finer particles are repre- take years to complete; it is a slow, painstaking pro- sented by siltstone and mudstone. Cobbles and peb- cess that requires patience and persistence. bles laid down by swift rivers during the Mesozoic If sedimentary rock layers can be thought of as are now recognized as conglomerates, which appear the pages in a natural history book, then sequences somewhat similar to concrete. These layers or strata of layers might be regarded as chapters. By conven- represent the pages of nature’s autobiography, for tion, geologists have described successive layers of they record the conditions and life of a former Utah. sedimentary rock that record a particular chapter Sedimentary rocks form at the surface of the in geologic history as a formation. A formation is a earth, under conditions that we can directly sequence of rock layers that have similar character- observe, so it is often possible to determine the istics such as grain size, composition, and bedding environment in which they were deposited with thickness. The combination of such features serves some degree of certainty. For example, by studying to distinguish the rocks in a particular formation The Mesozoic World 13

1.9. Sedimentary deposits associated with river systems. Note the complex intermingling of various types of sediment and the rapid lateral changes from one type of deposit to another. The layers and lenses of sand, gravel, silt, and clay record both the lateral movement of shifting rivers and the accumulation of sediment through time. from other layered sequences above and below it. Entrada Sandstone and the Tropic Shale. As an illus- The rocks that make up a formation are more or less tration of the abundance and diversity of Mesozoic uniform in their characteristics, representing sedi- rocks in Utah, over two hundred different forma- ment that accumulated under similar conditions in tions of this age are recognized in the state. similar environments. The boundaries between suc- The Mesozoic rocks of Utah that produce dino- cessive formations are placed where the characteris- saur fossils consist mostly of sediment that was tics of the rocks change: for example, where coarse deposited on land in places such as streambeds, sandstone is overlain by a sequence of fine mud- floodplains, lakes, swamps, and sand dunes. Sed- stone layers. Such shifts represent changes in the iment that accumulated under the Mesozoic seas nature of sediment accumulation, which in turn that covered parts of Utah has also produced dino- suggest changes in the environment of deposition. saur fossils, but this is relatively rare. Land-depos- Formations, then, represent chapters or phases of ited (terrestrial) sediments typically accumulate in more or less constant conditions in the overall con- localized areas under the influence of rivers, wind, tinuum of environmental change recorded by suc- gravity, or ice. Oceanic sediments, in contrast, form cessive formations. vast layers of mud and ooze that blanket extensive Formations are generally named for the locali- tracts of the seafloor. Consequently not many Meso- ties where the rock unit is particularly well exposed zoic formations in Utah have broad lateral extent. or was first studied and defined. Cedar Mountain, With a few exceptions, most are restricted to a rel- for example, is the highest point in the San Rafael atively small area. This is one reason why so many Swell of central Utah. The Cedar Mountain For- different formations have been identified in the mation consists of sedimentary rocks that are best Mesozoic sequence of Utah. The Mesozoic rock exposed in that location, even though the layers record of Utah is heterogeneous, changing in char- extend beyond the mountain itself and have been acter as you move from place to place. For example, identified in many other regions. When a partic- the late Cretaceous strata in Utah include conglom- ular type of rock represents nearly all of a forma- erate in Echo Canyon near Salt Lake City, sandstone tion, the word “formation” is occasionally replaced near Ferron in central Utah, coal in the Book Cliffs with an epithet reflective of that dominant lithology region, shale in the Hanksville Basin, and mudstone (rock type). Such is the case in formations like the almost everywhere else. Such variety is a general 14 Chapter 1 characteristic of any sequence of sedimentary rocks basin during the late Jurassic period. The portion deposited on land, and the dinosaur-bearing rocks of it in central Utah that consists of river-depos- of Utah are certainly no exception. Figure 1.9 illus- ited sandstone and conglomerate is known as the trates some of the different types of sediment that Salt Wash Member, while the other members of the can be deposited in a terrestrial setting. Morrison consist of other types of sediment that Another factor that limits the extent of any accumulated in slightly different environments. formation is erosion. It has been at least 65 mil- In a similar manner it is sometimes feasible lion years since the Mesozoic formations of Utah to combine several formations into larger enti- were deposited; for some of them, over 200 mil- ties known as groups. A group is a set of formations lion years have elapsed. The blanket of sediment with some overall similarity, even though they differ that originally accumulated may have been par- individually. For example the Glen Canyon Group tially removed by subsequent erosion so that the in southeastern Utah consists of (in ascending rock layers now cover only a fraction of the area order) the Wingate Sandstone, the Kayenta Forma- that they once occupied. Geologists can trace some tion, and the Navajo Sandstone. All three of these formations from one isolated locality to another, early Jurassic formations are dominated by sand- across the erosional gaps, by a practice known as stone, but the details of their textures, compositions, correlation. Recall, however, that land-deposited sedimentary structures, and other features are indi- sedimentary rocks typically exhibit pronounced vidually distinctive. Thus, although all three for- lateral variations. Consequently we may observe mations consist principally of sandstone, different coarse sandstone in one locality; but by the time we kinds of sand were deposited under different con- have traced (or “correlated”) it to a distant expo- ditions in the three components of the Glen Can- sure, the sandstone interval may be represented yon Group. As in the case of formations, groups by conglomerate, limestone, or shale. In such and members are also named in reference to geo- instances, we might be tempted to assign the rocks graphic localities where the constituent strata are of the two separated localities to different forma- well exposed or first studied by geologists. tions because they are composed of different mate- During the long span of the Mesozoic a vari- rials, even though they accumulated at the same ety of sediments accumulated in central and south- time. This practice has further contributed to the ern Utah. At times great rivers ran through the proliferation of formation names for the Mesozoic region, depositing varying kinds of sediments in rocks of Utah. their channels and on the adjacent floodplains (fig. In many cases it is possible to subdivide a for- 1.9). At other times dry winds blew great volumes of mation into smaller sequences or intervals that sand into the region to form extensive dune fields. represent a variation of the overall geological char- Oceans occasionally penetrated into Utah, and the acteristics. Such subdivisions of formations are rock record of these intervals is dominated by sed- called members. The Morrison Formation, a famous iments that accumulated on the shallow seafloor dinosaur-producing formation in the Rocky Moun- or along the beaches and coastal plains bordering tain region, has been split into at least three mem- the seas. Because the environments were constantly bers in most Utah exposures: the Brushy Basin changing and never uniform across the entire Member, the Salt Wash Member, and the Tidwell region, the sedimentary record of these Mesozoic Member. Additional members may be present events is a rather complex mixture of sandstone, in some exposures of the formation. The Morri- mudstone, conglomerate, shale, coal, limestone, and son Formation consists of a heterogeneous mixture other types of rocks. These are sediments that con- of sedimentary rocks deposited in a large interior tain the fossils of Utah’s dinosaurs. The Mesozoic World 15

1.10. Outcrops of bentonitic mudstone of the Morrison Formation weathering into a “popcorn” surface north of Capitol Reef National Park. Photo by Frank DeCourten.

Dinosaurs and Volcanoes in and around Utah clay minerals that form the rock known as ben- Many depictions of the Mesozoic landscapes of tonite. Many of the dinosaur-producing mudstone western North America feature volcanic peaks sequences in Utah and adjacent regions are “ben- looming on the horizon and sometimes even an tonitic,” meaning that they are rich in this weathered actively erupting volcano. The varied Mesozoic form of volcanic ash. Bentonite is highly absorbent rock record of Utah does in fact indicate that volca- and expands significantly when it is moistened by nic activity was taking place near or in Utah during rain. As wet bentonite dries, it shrinks and cracks much of the era. In particular we know that cen- to produce the “popcorn” surface so characteristic tral Arizona, eastern Nevada, and southern Idaho of the dinosaur-bearing badlands of Utah (fig. 1.10). were the sites of numerous Mesozoic eruptions. Much to the dismay of paleontologists and other Eastern Utah was thus surrounded by volcanically back-road travelers in eastern Utah, wet bentonite active regions. From time to time great clouds of also turns into a nearly frictionless slime, immobi- volcanic ash that were discharged from the erupt- lizing even four-wheel-drive vehicles in intractable ing volcanoes drifted over the Utah region to settle muddy bogs following rainstorms. out as relatively thin sheets across the floodplains, Sometimes the ash layers, usually only a few dunes, lakes, or river channels. Some of the volca- inches thick, were quickly buried under additional nic ash was reworked by wind or water to become layers of sediment and experienced little weather- mixed with the silt and mud that was being depos- ing or disruption. Such layers of ash are sometimes ited at the time. As it weathered, the ash produced found sandwiched between sandstone, siltstone, or 16 Chapter 1

datable ash layers are scattered through the Meso- zoic rock sequence in Utah. Their presence in dinosaur-bearing sequences allows us to estimate the times when the various types of dinosaurs lived in Utah by providing temporal reference points in the sedimentary record. For example, at the Cleveland- Lloyd Dinosaur Quarry, the bone-producing horizon in the Morrison Formation is situated between two layers of slightly altered volcanic ash that still contain datable minerals (fig. 1.11). The layer above 1.11. The Morrison Formation at the Cleveland-Lloyd the quarry yields a radiometric date of about 147 Dinosaur Quarry in Emery County. Data from Bilbey million years, and the layer below is about 152 mil- 1992 (cited in chapter 5). lion years old (Bilbey 1992 in chapter 5 references). We can estimate, then, that the dinosaurs preserved mudstone in Utah’s Mesozoic formations. Though at this site lived in Utah 147–152 million years ago. they represent only a small fraction of the Meso- Without the datable minerals derived from the vol- zoic rock record, the thin volcanic ash layers are canic ash, all we could say is that the Cleveland- extremely important. This is because the ash, and Lloyd dinosaurs were “late Jurassic” in age, a time less frequently the bentonite, contains minerals span encompassing more than 16 million years from that can be dated with techniques that rely on the 161 to 145 million years ago. The ashy materials in gradual decay of radioactive elements. While it is the Morrison Formation at this locality allow us to beyond the scope of this book to review the pro- estimate the absolute ages of dinosaurs with much cess in detail, these techniques (collectively known greater precision than would otherwise be possible. as radiometric dating) can provide reasonably precise dates for the formation of the ash layers. Only The Dinosaur Fossil Record the ash particles can be give reliable dates of accumulation, because the grains that compose the bulk As we explore the dinosaurs of Utah in this book, of the sedimentary rocks were derived from bed- it is best to be mindful of the limitations of the evi- rock of varying ages and locations. The radiomet- dence upon which we base our reconstructions of ric ages of a sand grain in a sandstone, for example, these extinct animals and the vanished world they would give us an indication of the time when the inhabited. Even though paleontologists have been grain formed, not necessarily the time when it was studying dinosaurs for more than 150 years, we still deposited in Utah. have many lingering questions and nagging uncer- Only the volcanic sediments can provide mean- tainties about them. Many of these mysteries are ingful radiometric dates, for they often contain dat- attributable to the imperfections of our primary able minerals that formed at essentially the same data on dinosaurs, the fossils recovered from Meso- time when the ash accumulated. Of course, not all zoic strata. ash layers can be reliably dated. To be datable, the Dinosaur fossils are more varied than most ash must not have weathered excessively prior to its people suspect. When people think of dinosaur fos- burial and must contain certain mineral crystals, sils, most immediately envision a preserved skull or such as the mica biotite or the feldspar sanidine, perhaps a skeleton entombed in rock. Many such which have enough radioactive elements (potas- fossils have indeed been discovered, but they are sium in this case) to be accurately measured. Many exceedingly rare. Much more commonly we find The Mesozoic World 17

1.12. Dinosaur footprints, such as this one near St. George, record information about the size, posture, foot anatomy, and movement of the animals that made them. Photo by Frank DeCourten. only partial skeletons or a few single isolated bones (or even fragments of them) preserved in varying degrees of perfection. It is always a challenge to accurately identify such scrappy remains, let alone reconstruct the entire skeleton of an extinct ani- 1.13. Rounded and highly polished stones, such as these mal. Aside from bones and teeth, though, we can from Cretaceous strata in the San Rafael Swell, may represent gastroliths or “stomach stones” of dinosaurs or gain additional information from other kinds of other reptiles. Courtesy John Telford. dinosaur fossils. The footprints and trackways of dinosaurs and other terrestrial creatures have been a replica in the surrounding sedimentary rock. Like found in many places in Utah (fig. 1.12), sometimes footprints, skin impressions do not represent the in spectacular abundance. Footprints are known preservation of the actual body tissues but can still as trace fossils, because they do not represent pre- provide a great deal of information on the struc- served remains of organic tissues. Nonetheless, they ture and appearance of the integument (body cover- can provide a surprising amount of information on ing) of dinosaurs. Features such as scales and scale aspects of dinosaurs such as their foot morphol- clusters, nodes of dermal bone, skin folds, and wrin- ogy, style and rate of locomotion, migratory behav- kles can be faithfully recorded as skin impressions. ior, community structure, and biodiversity. In many In recent years many dinosaur eggs, eggshells, and Utah localities, such as the southwestern portion nesting sites have been discovered. From these we around St. George, dinosaur tracks are much more have learned much about the nesting habits, pat- abundant than preserved bones. Most of what has terns of embryonic development, and reproduc- been learned about the early Jurassic dinosaurs of tive behavior for some types of dinosaurs. While we that area is based on the analysis of their trace fos- have not yet found completely preserved dinosaur sils (see chapter 3). nests or intact eggs in Utah, fragmentary eggshells Another type of trace fossil important in the and partially preserved eggs are common in some of study of Utah’s dinosaurs is skin impressions. These the Mesozoic rock units discussed in later chapters. impressions are formed when soft sediment accu- Gastroliths (“stomach stones”) are very common mulates over and around a dinosaur carcass. After in several different dinosaur-producing rock forma- the remains are buried, the soft tissues decompose, tions in Utah (fig. 1.13). These smooth, rounded, and leaving the surface features of the skin preserved as highly polished stones are interpreted to be gizzard 18 Chapter 1 stones and suggest that at least some dinosaurs had remains. The by-products of microbial decomposi- such an organ to supplement their dentition in the tion include toxins and gases that cause the carcass processing of food. In this regard some of the her- to bloat and result in the characteristic odor of rot- bivorous dinosaurs might have been similar to the ting flesh. Scavenging animals soon are attracted to modern birds. On rare occasions we sometimes the remains. Ravens, vultures, coyotes, and other find fossilized dinosaur droppings, known as copro- creatures arrive at the scene to consume portions of lites, or even the stomach contents, preserved after the carcass. Perhaps the scavengers remove a leg, a the soft tissues of the dinosaur have decayed. Such portion of the back, or a shoulder. Parts of the car- objects can provide information about the diets of cass eventually disappear. Insects attack the remain- dinosaurs, the structure of their digestive tracts, and ing carcass, often laying eggs in the rotting flesh, the ways in which their food was processed. Com- which serves as food for the larvae that soon hatch. bined with the preserved bones and teeth, all of these When all the soft tissues have been consumed by accessory fossils provide us with a wealth of infor- microbes, scavengers, or insects, the remaining mation about Utah dinosaurs. But how good is the bones become scattered as the connective tissues fossil record of dinosaurs? How complete and accu- (ligaments, tendons, and cartilage) no longer hold rate a picture of dinosaurs can we reconstruct on the the bones together. The isolated and scattered bones basis of this tangible evidence of the distant past? lie under the sun and eventually become bleached We must really ask ourselves two questions about and cracked as they dry out. Then various rodents the adequacy of the fossil record of dinosaurs. First, appear to gnaw on what’s left of the bones. Inevita- is fossilization common enough to give us a reason- bly, even the most durable tissues such as teeth and ably complete sampling of the dinosaur populations hooves are reduced to splinters and powder under that inhabited Utah during the Mesozoic? Second, the combined attack of physical decay and biologi- are the data that we have biased in any way that cal decomposition. Within a few months or perhaps might affect our perceptions of the relative abun- a year or so, no trace of the sheep carcass remains. dance and the anatomy of the various dinosaurs? The existence of the sheep has not been recorded in Paleontologists almost universally agree that the the fossil record of the future. answer to the first question is “no” and the answer Fossilization of any organic tissue is possible to the second question is “yes.” The fossil record of only if the normal process of postmortem decay and the dinosaurs is undoubtedly a numerically poor decomposition is interrupted before all the remains sample and is also highly biased. Let’s explore the disintegrate completely. One way to do that is to reasons why. bury the carcass of the animal soon after its death, before the microbes, scavengers, and the elements Numerical Quality of the Fossil Record can get to it. If by chance an animal dies while it is If we look around at the modern world, we crossing a river or standing along the edge of a lake soon become familiar with the normal sequence of or climbing through sand dunes, preservation of its events that follows the death of any organism that remains is much more likely. But even in these cases lives on land. Consider, for example, the ultimate fossilization is not guaranteed. A carcass floating in fate of a sheep that dies from natural causes dur- a river can still be completely decomposed. For any ing the summer on a tract of Utah rangeland. After of its tissues to be preserved, the animal must die in death, the normal immunological defenses that the just the right spot along the river, where sediment is sheep enjoys during life no longer operate. Decom- actively being deposited. Perhaps death occurs while position begins on the microbial scale as bacteria the creature is walking along a sandbar. In that case and other organisms begin to flourish in the sheep’s the sand and silt may pile up and cover the carcass The Mesozoic World 19 before decomposition advances very far. Yet how minuscule fraction of animals that become buried often are carcasses buried in this manner? Certainly immediately after death, an even smaller number of it is a rare event. The process of fossilization begins them will ever become fossilized. only when such rare and fortunate (for the paleon- Finally, remember that for a fossil to be use- tologist, at least) conditions are met. In many cases ful to us someone has to discover it. This, of course, only a portion of the carcass may be buried prior to requires that the buried and preserved remains complete decomposition, allowing a partial skele- somehow must find their way back to the earth’s ton, perhaps a only single bone, to escape decay. The surface. This usually requires geologic uplift of the vast majority of dinosaurs (or any animal for that region, which initiates erosion that in turn wears matter) that ever lived on the earth’s surface disap- away rock layers as they are elevated to expose the peared without a trace, as their remains underwent formerly buried strata. Fossils emerge only when the the normal process of complete decomposition. rock layers that contain them crumble and decay at Even after burial, fossilization is still not assured. the surface. Unless someone appears at just the right In the geological environment, organic materials are time, the fossils will also succumb to the agents of not always stable. Microbial decay can still occur. weathering and erosion. So finding a fossil requires Fluids moving through the sediment, either before good timing: if we arrive at the scene too early, ero- or after it hardens into stone, can dissolve some of sion will not have exposed the fossils to view; if we the hard tissues or obliterate them beyond recogni- are too late, erosion will have obliterated the fossil. tion. Sometimes, though, the buried remains can be In either case we do not have the information that altered in such a way as to increase their stability in the fossils convey. In light of these considerations, the geological environment. For example, the open we must acknowledge that only a small fraction of spaces in porous tissues such as bone or wood can all the dinosaur fossils that exist have been discov- become filled with minerals such as silica (SiO2) or ered and studied. calcium carbonate (CaCO3). This process is known In summary, then, the fossil record of any group as permineralization and is a very common mode of of prehistoric animals represents nothing more than preservation in dinosaur fossils. Other methods of a tiny representation of the original population. The stabilizing biological remains in the geologic envi- fossil record is a numerically poor sampling. Pale- ronment include the complete replacement of the ontologists universally agree that only a small per- organic tissues by mineral substances and the for- centage of all the creatures (estimates vary from mation of natural replicas of the remains known as a fraction of 1 percent to 3 percent) that have ever molds and casts, among many others. Many dino- lived on the earth are known from the fossil record. saur fossils are preserved through a combination of For dinosaurs the percentage may be a little higher these processes. The dinosaur bones from Dinosaur due to the frenzied collecting that began in the late National Monument, for example, have been partly 1800s and continues today. D. A. Russell (1995) has permineralized by silica and iron oxide, while some estimated that about 8 percent of all dinosaurs that of the original tissues have been replaced with cal- ever existed have been identified by paleontologists. cium compounds (Hubert and others 1996). If some Recent statistical analyses of dinosaur family trees form of stabilization does not affect the original and the fossil abundances suggest that probably at organic material, it is unlikely that very much of the least three times more dinosaurs remain to be dis- buried carcass will survive millions of years of expo- covered than have been identified thus far (Heath- sure to the high temperatures, enormous pressures, cote and others 2005; Wills and others 2008). and reactive chemicals present in the hostile geo- In any case the number of known dinosaurs is logic environment. So, even if we consider only the relatively small. This means that we are basing our 20 Chapter 1 perceptions on fragmentary material representing Almost certainly they existed; but the alpine dino- an extremely restricted view of the Mesozoic bio- saurs would be much less likely to be preserved as sphere. Being aware of this limitation of the fos- fossils because mountains and uplands are charac- sil record of dinosaurs should not make us any less terized by vigorous erosion, not by deposition of enchanted by the creatures. Tens of thousands of sediment. Nearly all of what we know about dino- dinosaur bones are preserved in museums all over saurs comes from the study of the lowland dwell- the world, and many more dinosaur fossils await ers that dominate the fossil record of this group of discovery in Utah and elsewhere. If we accept the reptiles. notion that fossilization is an extremely rare event, Paleontologists universally acknowledge another then every dinosaur bone represents literally mil- kind of bias in the fossil record: the anatomical bias lions of animals that did not leave any evidence of means that certain tissues and parts of dinosaurs are their existence. To be preserved in the fossil record preserved more often than others. Clearly the hard at all, any group of organisms had to be abundant, tissues such as bones and teeth will more commonly diverse, and persistent during its time. Collectively survive the processes of decomposition, weathering, the dinosaur fossil record may be a meager sam- burial, and postburial degradation to become fos- ple of the original dinosaur populations. But under- sils than the less durable portions of the anatomy. standing the limitations of the data allows us to For this reason we know next to nothing about the realize that these ancient reptiles were one of the details of dinosaur eyes, hearts, or kidneys. As we most successful groups of animals to ever inhabit have learned earlier, now and then we get insights the earth. Besides, for all its numerical deficiencies, concerning the soft tissues of dinosaurs from trace the fossil record of dinosaurs is all that we have; fossils, gastroliths, and skin impressions; but unless there is no alternate source of information to con- the soft organs of dinosaurs left some scar or feature sult. The fossils, along with our skills in interpreting on bone, we can usually study them only through them, still allow us to formulate some valid percep- inference and comparison with living animals. tions of these fascinating creatures. In some cases it is possible to acquire information about soft tissues from the bone(s) that Biases in the Dinosaur Fossil Record enclosed them. For example, we do know some- A moment’s reflection about the process of fos- thing about the overall morphology of dinosaur silization leads us inevitably to another conclu- brains because many brain cavities have been iden- sion about the dinosaur fossil record: it must also tified in well-preserved skulls. From these cavities be highly biased in a number of ways. Consider, we can produce casts (usually of latex or plaster) for example, the likelihood of a habitat bias. Some that allow us to determine the size and shape of the dinosaurs, those living in habitats where sediment brain, the location and arrangement of lobes within accumulates in great quantities, will probably be it, and the branching pattern of major nerves. But preserved more often as fossils than other dinosaurs we know nothing of the brain tissues themselves. In living elsewhere. Consequently dinosaurs adapted a similar manner we can estimate the size and shape to swampy or riparian (adjacent to rivers) habi- of organs such as lungs and intestines by observ- tats might be expected to leave more abundant fos- ing the configuration of the rib cage or the pelvis of sils behind, because in those locations sediment is dinosaurs, but no one has any precise understand- continuously deposited. But what about the upland ing of the anatomy of these organs. dwellers? Were there montane dinosaurs in the Even among the harder tissues of dinosaur bod- Mesozoic, living in habitats now occupied by ani- ies there is a bias: small and delicate bones are mals such as mountain goats and bighorn sheep? much less common as fossils than the more massive The Mesozoic World 21 elements such as limb bones and armor plates. the collections of dinosaur fossils that now exist Thus the fossil record of dinosaurs is highly biased in museums all over the world are strongly biased toward teeth (many species of dinosaurs have been toward the larger types of dinosaurs. We know that named solely on the basis of teeth or even a single many dinosaurs were relatively small creatures, even tooth fragment), the larger and more robust bones, when fully grown. Compsognathus, a small thero- spikes, and claws. This imperfection reflects the ana- pod, was not much larger than a modern rooster, tomical bias of fossilization. and the ornithopod Hypsilophodon was generally In addition, we anticipate that the fossil record about the same size as a large domestic turkey (Cal- of dinosaurs is also biased toward some kinds of lison and Quimby 1984). A recent analysis of body dinosaurs. We might call this the systematic or tax- size estimates for dinosaurs has shown that some 26 onomic bias. For example, some of the smaller and percent of all known dinosaurs weighed less than more birdlike dinosaurs had very delicate, partially about 220 pounds, the approximate weight of a large hollow bones. Their remains are not nearly as com- human (Peczkis 1994). Even though only 14 percent mon in the fossil record as are the massive bones of the known dinosaurs are truly gigantic animals of the lumbering sauropods, such as Apatosaurus (22,000–220,000 pounds), this same study revealed or Diplodocus. Even though they might have been that dinosaurs in this size range accounted for 36 living in the same area and in equal numbers, the percent of the material collected during the early giant sauropods will leave behind many more obvi- “bone rush” period from 1870 to 1900. This clearly ous fossils than the smaller, more lightly built crea- illustrates the historical collecting bias in favor of tures. We may, if we are not careful, conclude that the fossils of the larger dinosaurs. While some dino- the little dinosaurs were very uncommon because saurs were clearly the largest terrestrial animals we find very few fossils. In fact they may have been ever to exist on the earth, most were not behemoths extremely abundant, but their small and delicate of such colossal proportions. Fortunately, mod- bones were only infrequently preserved as fossils. ern paleontologists seeking to understand the entire Finally, it is important to remember that paleon- Mesozoic ecosystem are starting to correct this his- tologists have exhibited a historical preference for torical collecting bias toward larger forms. As later large dinosaur fossils. This has led to another type of chapters demonstrate, some of the most success- bias in the dinosaur fossil record: the collecting bias. ful and intriguing dinosaurs in Utah were relatively Ever since dinosaurs were first discovered, people small by dinosaur standards. have been awestruck by their gigantic proportions. In summary, the fossil record of dinosaurs is a As museums began to exhibit skeletons of dino- numerically poor sampling of the original Meso- saurs, the clear emphasis was on size—the bigger zoic population and is strongly biased in terms of the dinosaur, the better. Furthermore, large fossil the habitat preferences, anatomy, and types of crea- bones are hard to miss in the field. The 6-foot-long tures that it reveals to us. Nonetheless, a great deal (2-meter) femur of an Apatosaurus weathering out can still be learned from the fossil record about the of a hillside would not go unnoticed for long. You nature of dinosaurs, their evolutionary history, and have to look harder to find the bones of small dino- the manner in which they interacted with the con- saurs. Certainly many small fossil bones were left stantly changing Mesozoic environment. While we behind in favor of the larger, more obvious bones should always keep the limitations of our basic data by collectors of the late 1800s and early 1900s. Only in mind, we should not be discouraged. It is true during the past fifty years or so have paleontologists that many mysteries concerning the dinosaurs and been carefully looking for small bones and collect- the world they inhabited still linger, even after more ing them from dinosaur quarries. For these reasons than 150 years of fossil collecting and analysis. But 22 Chapter 1 however incomplete our knowledge of Utah dino- handled ignorance very well: ever since humans saurs may be, it is still substantial, fascinating, and became human, we have been driven to expand certainly worth exploring in detail. our knowledge in the same way that Tyrannosaurus Only persistence and more fossils can lead us was driven to attack prey. This insatiable hunger for closer to a full understanding of dinosaurs and learning is the hallmark of our species, the quintes- toward solutions to some of the current mysteries. sential countenance of humanity. It is why we have Given the nature of the fossil record, we will prob- books, schools, libraries, computers, universities, ably never have answers to some of our questions. and museums. For those of us interested in dino- I, at least, am glad for that! For it is the myster- saurs, it is also why we love the Mesozoic wonder- ies and the uncertainties that motivate us as intelli- lands of Utah. gent and inquisitive creatures. Our species has never Chapter 2 Dawn of the Utah Mesozoic The Age of Dinosaurs Begins 02 The Triassic period, the earliest portion of the great supercontinental fragmentation began in the Mesozoic era, began about 251 million years ago. It Triassic. was one of the most interesting phases in the history As the global geography began to change dur- of the earth, a time of great change in land, life, and ing the Triassic, the global climate became modified climate. At the beginning of the Triassic the super- as well. Early in the Triassic much of the interior continent Pangaea had become fully assembled via of Pangaea was extremely dry, with monsoonal cli- the suturing of smaller land masses during the pre- mates developing in regions nearer the continental ceding Paleozoic era. This gigantic continent was margins, where brief wet intervals alternated with short-lived; by the end of the early Triassic it began prolonged droughts (Dubiel and others 1991). Under to show signs of its initial fragmentation. The core the dry conditions that prevailed in most of Pangaea of modern North America was part of a larger con- and Laurasia during early Triassic time, thick layers tinent known as Laurasia that began to separate of salt formed through the evaporation of large bod- from the rest of Pangaea along an enormous rift that ies of seawater, and extensive dune deposits accu- passed between Greenland and Norway, extended mulated inland. Both of these kinds of sediments south along the modern Atlantic coast (the New- are indicators of increasing aridity and are common ark Rift), and curved west into the Gulf of Mex- components of the Triassic rock sequences world- ico region (fig. 2.1). The rift zone was a depressed wide. Sedimentary rocks of this age are also so com- region of active faulting and intense volcanic activ- monly stained red by iron oxides that the Triassic ity, much like the modern East African Rift that sep- is known as the “great age of red beds.” Geologists arates Kenya and Tanzania from the rest of Africa. It continue to debate the climatic significance of the would take the remainder of the Mesozoic for North red beds, but most believe that they indicate a warm America to become fully detached from Pangaea and probably dry climate. as the modern Atlantic and Gulf of Mexico ocean These changes in the geography and climate of basins developed. But the initial rumblings of this the world stimulated some fascinating patterns of

2.1. Global geography in the Triassic. North America was part of Laurasia 250 million years ago as Pangaea began to break apart. Reconstruction from Ronald Blakey/Colo- rado Plateau Geosystems, Inc. Used with permission.

23 24 Chapter 2 evolution among the flora and fauna during the Triassic period. As noted in chapter 1, the Trias- sic was the time of the great reptilian radiation on land and in the sea. The Permo-Triassic extinctions had cleared many of the major ecologic niches in both the terrestrial and marine realm of their primary late Paleozoic occupants. On land the reptiles were the principal beneficiaries of the evolutionary opportunities created by the extinctions. So many different groups of reptiles developed during the transition from the Paleozoic to the Meso- zoic that the Triassic assemblage is a confusing and complex array of rapidly evolving lineages. To complicate matters even more, some of the Trias- sic reptiles, such as the mammal-like therapsids, represent “holdovers” from the earlier late Paleo- 2.2. Cladogram of the diapsid reptiles. The Ornithodira zoic aggregate. The ancestors of the dinosaurs were includes birds and dinosaurs that are more closely included somewhere in that complex hoard of rep- related to the crocodiles than they are to lizards and tiles, accompanied by many other specialized rep- snakes. tiles representing separate lineages. While it is impossible to review all the different clades, a natural grouping that includes only evolu- groups of early Triassic reptiles fully here, it is help- tionarily related animals. Clades do not have a tax- ful to identify two broad categories before we exam- onomic rank such as family, order, or phylum but ine the Triassic vertebrate fossils from Utah and may consist of many such groups. A clade can be adjacent areas. Recall that dinosaurs belong to a large considered a discrete branch on the tree of life, sep- group of reptiles known as the Diapsida in reference arate from all other branches. In addition, the con- to the two temporal openings in the skull (see the cept of a clade can be used to subdivide a large appendix for more details). This large group includes group (like the diapsid reptiles), into smaller units dinosaurs, birds (direct dinosaur relatives), croco- of more closely related creatures, known as sister diles, snakes and lizards, pterosaurs, and many other groups or subclades. A cladogram is a graphic rep- extinct groups. Lizards and snakes separated from resentation of the relationships between evolution- the other archosaurian diapsids in early Triassic time arily related groups of animals (fig. 2.2). The greater as a separate group, the Lepidosauria. Our princi- the separation between the groups represented pal interest is in the remaining archosaurs, because on a cladogram, the more distant is the relation- the dinosaurs, their ancestors, and their descendants ship between them. Thus each branch on the tree of are all found within this group. As part of the great life may have numerous smaller branches diverg- reptilian radiation of the early Triassic period, the ing from it; but any branch can be a clade, regard- archosaurs diverged into two main groups: the Pseu- less of how many subbranches it contains. One of dosuchia (crocodilians and their relatives) and the the things that complicates the evolutionary history Ornithodira (a group that includes the dinosaurs of the dinosaurs is that they evidently arose during and birds, along with the ancestors of both). the time when many different clades were diverg- These three groups—the Lepidosauria, the Orni- ing from the reptilian trunk of the tree simultane- thodira, and the Pseudosuchia—can be considered ously. The great burst of reptilian evolution created Dawn of the Utah Mesozoic 25

skeletal features as either primitive (plesiomorphic) or advanced (apomorphic) and reconstructing the branching pattern accordingly. This requires some judgments that might change in light of new fossil discoveries. Finally, a clade can be defined in different ways; various scientists may apply different names to a given group. Paleontologists are in general agreement that the three clades we have identified are valid, but revisions may occur as we learn more about the earliest dinosaurs and their relatives. Let’s examine some of the more common reptiles known from the early Triassic strata of the Utah region to illustrate the variety of creatures that existed as the first dinosaurs appeared. The phytosaurs (fig. 2.3B) are one of the most common pseudosuchian reptiles found in the Trias- sic rocks of the Southwest. These semiaquatic reptiles were predators that looked much like modern crocodiles and seem to have lived in or near rivers. With long pointed snouts and jaws lined with sharp conical teeth, the phytosaurs were probably voracious predators of fish and smaller reptiles living in the rivers that they inhabited. The largest phytosaurs were nearly 20 feet (about 6 meters) long. Aetosaurs (fig. 2.3C) were also crocodilelike in their general body plan, but these animals were herbivorous and possessed heavy plates of bony armor (scutes) along with prominent defensive spikes in the shoulder region and along the flanks. Some of the aetosaurs had blunt snouts, evidently for rooting through 2.3. Nondinosaur vertebrates of the late Triassic Chinle plant litter and soil, along with leaf-shaped teeth for Formation of the western United States: A. Metoposau- rus, a carnivorous amphibian; B. Rutiodon, the most shearing vegetation. These features suggest that they common of the pseudosuchian phytosaurs; C. Desma- ate roots, low-growing shrubs, or aquatic plants tosuchus, a herbivorous semiaquatic aetosaur; D. Place- growing in or along the banks of Triassic rivers. rias, a dicynodont therapsid reptile; E. Paradapedon, a Rauisuchians include several types of carniv- rhynchosaur with a skull 6 inches long; F. Hesperosu- chus, a small lizardlike pseudosuchian; G. Postosuchus, orous pseudosuchian reptiles that were quadru- a large rauisuchian with a skull 2 feet long. A–D and F: pedal with more or less erect limbs and thus were from Colbert 1972; E: from Carroll 1988 (cited in chapter better adapted for terrestrial locomotion than 1 references); G: after Chatterjee 1986. the phtyosaurs and aetosaurs. The largest rauisuchian in North America was Postosuchus, a 12-foot- a confusing array of reptiles that paleontologists are long (4-meter) predator that probably weighed in still trying to sort out. Be mindful as well that clades at some 400 pounds (fig. 2.3G). The rauisuchians are constructed by paleontologists by identifying looked a bit like massive long-legged alligators. 26 Chapter 2

Dicynodonts (fig. 2.3D) were large plant-eat- their contemporaries from the Triassic. With limbs ing mammal-like reptiles (therapsids) that typically positioned directly beneath the body and ankles and had paired tusks for rooting. The dicynodonts were feet designed for swift walking or running, these squat and thick-bodied, with large heads tipped creatures became extremely successful and varied, with a beaklike apparatus. Canadian paleontolo- eventually developing carnivorous members that gist D. A. Russell refers to the dicynodonts as “cow- were at least partially bipedal. Were these the ear- turtles” (Russell 1989). The name is fitting, for it liest dinosaurs? The question is difficult to answer, describes their general appearance and is also sug- because the evolutionary trend toward increasing gestive of the combination of reptilian and mamma- land mobility (including bipedal stance) was occur- lian skeletal features. The therapsids also included ring in several different lineages within different some carnivorous forms, known as cynodonts, that archosaur clades. The term “convergent evolution” had an overall doglike appearance. is used to describe the development of similar fea- Rhynchosaurs were squat, rather piglike herbivo- tures in separate lineages through natural selection rous reptiles represented by Paradapedon (fig. 2.3E), for similar traits. It now appears that the traits that one of the most common North American mem- distinguish the dinosaurs were developing to differ- bers of the group. The bones forming the snout of ent degrees in several groups of archosaurs during most rhynchosaurs curved over the lower jaw to Triassic time. form a prominent “overbite.” This feature, coupled No one knows for sure where or exactly when with small peglike teeth, probably allowed the rhyn- the first dinosaurs originated. South America chosaurs to root through soil and plant litter to find seems to have many candidates for the “first dino- their fodder. saur” award, and many paleontologists believed In addition to these extinct groups of reptiles, the until recently that this continent was the cradle earliest representatives of more familiar forms also of the Dinosauria. Staurikosaurus, a 6-foot-long emerged during the Triassic. The remains of prim- (2-meter) bipedal predator from Brazil, seems to itive members of the turtle (anapsid reptiles) and be on the threshold of the Dinosauria, because lizard clans (lepidosaurs) can be found in rocks of the pelvis has a small opening in it for the end of Triassic age. The earliest ancestors of the archosaurs the femur and the hind limbs were evidently posi- (true crocodiles, dinosaurs, and birds) were also tioned vertically beneath the body. Its bones were emerging at about the same time. The landscapes of recovered from rocks that are not precisely dated the world were definitely covered with reptiles dur- but seem to be between 235 and 225 million years ing the Triassic. old (middle Triassic age). Staurikosaurus is so Other than the early ornithodirans, none of primitive in other aspects of its skeleton, however, the groups of reptiles identified above are closely that it cannot be confidently assigned to either related to the dinosaurs. Sometime in the early Tri- the Ornithischia or the Saurischia. Other, perhaps assic, among the ongoing reptilian riot, a group slightly younger, South American reptiles are sim- of slender-legged, mostly quadrupedal carnivores ilarly dinosaurlike but are comparatively primi- emerged. This set of reptiles has traditionally been tive. Herrerasaurus and Eoraptor, for example, are assigned to the group known as the “thecodonts,” both extremely “dinosaurian” bipedal carnivores many of which are now thought to be primitive from the late Triassic of northwestern Argentina. ornithodirans, the group to which the dinosaurs Of the two, Eoraptor is more primitive and lacks belong. Several Triassic ornithodirans might be con- some key features of the Dinosauria. Herrerasaurus sidered dinosaur ancestors, because they were evi- is more typical of later theropods but is still primi- dently better adapted for terrestrial locomotion than tive in comparison to the true theropod dinosaurs. Dawn of the Utah Mesozoic 27

2.4. Global distribution of dinosaur clades in the late Triassic. Graphic from Parker and others (2005), reproduced by permission of the Royal Society.

To make matters even more intriguing, a contem- skeletal features. The remains of a relatively large porary dinosaur from the same area, Pisanosaurus, quadrupedal sauropod dinosaur are known from is clearly related to the ornithischian dinosaurs. Triassic rocks in South Africa that are poorly dated Pisanosaurus was unquestionably a plant-eater, as but clearly demonstrate the presence of true dino- evidenced by its well-worn simple teeth, but it did saurs in the mid-Triassic (Yates and Kitching 2003). not have the fully developed “dinosaurian” type On the nearby island of Madagascar vertebrate of ankle. Scientists continue to debate whether or remains have been uncovered that likely represent at not Pisanosaurus represents the oldest ornithis- least two species of plant-eating dinosaurs known as chian dinosaur or something close to the ancestor prosauropods (Flynn and others 2009) from rocks of that group. The absolute age of these specimens that are 225–230 million years old. Footprints and is somewhat uncertain; most evidence suggests body fossils in Poland suggest the presence of dino- that they are around 228 million years old (Rogers saurs in Europe as early as 250 million years ago, and others 1993). So we can conclude that the age very close to the beginning of the Triassic (Brusatte of dinosaurs was on the threshold of opening some and others 2011). 17 million years after the Triassic began in South Thus it appears that the dinosaurs first evolved America. By that time at least three groups of dino- within the ornithodiran lineage sometime in the saurlike creatures existed on that continent. early or middle Triassic, 240–250 million years ago, New evidence, however, suggests that the dino- but we can’t be certain where. Perhaps it was in saurs may not have originated in South America South America, Africa, or Eurasia. But wherever the after all. In Africa, for example, Euparkeria pos- dinosaurs first emerged from the confusing multi- sessed reduced forelimbs, suggesting that it was tude of Triassic reptiles, they were without doubt a beginning to use its hind limbs as the main method minor component of the terrestrial fauna. Several of propulsion. This predator looked for the most other groups of nondinosaur reptiles, including the part like a small carnivorous dinosaur and was pseudosuchians, appear to have been more abun- very similar to what many scientists perceived as dant and varied at the time the dinosaurs emerged. the archosaur ancestor of the first dinosaurs. Asil- It was not until after the end of the Triassic period isaurus, a quadrupedal omnivore 5–10 feet (1.5–3.3 that the dinosaurs became a prominent element in meters) long that was recently described from Tri- terrestrial vertebrate faunas. By that time their dis- assic rocks in Tanzania (Nesbitt and others 2010), tribution was nearly worldwide, with several major seems to have a mix of dinosaur and nondinosaur clades represented on most continents (fig. 2.4). 28 Chapter 2

Early Dinosaurs in North America tracts of dinosaur habitat. Utah would never have The first appearance of dinosaurs in North Amer- become populated by such a wondrous array of ica is difficult to determine with precision because dinosaurs had the stage not been set by the geologi- the rocks that formed during the time of their ori- cal upheaval during Triassic time. gin have not produced abundant fossils of terres- When the Triassic period began 250 million trial creatures. Enough is known from Triassic rock years ago, nearly all of western Utah was covered sequences, however, to indicate that the dinosaurs by a broad, shallow sea (fig. 2.5). The shoreline of arrived soon after the Pisanosaurus-Herrerasaurus- this sea extended north-south through central Utah Eoraptor assemblage emerged in Argentina. Sed- from roughly the southern border of the state to the iments of the Chinle Formation and Moenkopi eastern end of the modern Uinta Mountains, which Formation of the Colorado Plateau region, the Doc- were not yet elevated. Offshore from the coastline, kum Formation (or Group) of Texas, and the New- mud and sand were washed from the exposed land ark Supergroup (Cumnock, Pekin, and New Oxford to the east, settling on the ocean bottom to form Formations) of New Jersey have all produced dino- layers of shale, siltstone, and sandstone. Layers of saur bones. These strata are all about the same silty limestone accumulated elsewhere on the sea- age as or perhaps slightly younger than the dino- floor, where calcium carbonate was precipitated saur-bearing rocks of South America. Even though from ocean water. Today these marine sediments the fossil record of the first North American dino- of western Utah are represented by rock units such saurs is very sketchy, it appears that they achieved as the Thanyes, Dinwoody, and Woodside Forma- a worldwide distribution almost immediately after tions. Fossils of marine invertebrate animals such as their origin, wherever that event may initially have sea urchins, clams, brachiopods, and cephalopods occurred. Such rapid dispersal is reasonable given clearly indicate the oceanic nature of these depos- the great mobility of dinosaurs and the unified its. Sedimentary rocks of this general type and age nature of the world’s land masses during the later extend to the west across western Utah and Nevada, part of the Triassic. With a skeleton designed for suggesting that the open ocean stretched a consid- swift and efficient movement over land, and with erable distance in that direction. In central Nevada, few oceanic barriers to their migration, the world’s at the Berlin-Ichthyosaur State Park in northern first dinosaurs spread to every corner of Laurasia Nye County, muddy limestones of early Triassic age and Gondwana with remarkable swiftness. have produced spectacular fossils of these gigantic marine reptiles. So far we haven’t found any Trias- sic marine reptiles in western Utah, but they almost Utah in the Early Triassic certainly existed in the shallow water that covered The Triassic was a time of great change in the land that part of the state some 240 million years ago. and life of ancient Utah and adjacent regions. The East of the early Triassic coastline was a low plain changes that occurred in Utah during the Triassic that gradually ascended to highlands farther east. set the stage for events and landscapes that would Rivers draining more distant elevated areas flowed follow in later portions of the Mesozoic era. Utah sluggishly to the west and northwest (fig. 2.5), across landscapes and environments in early Triassic time the nearly flat coastal plain. The rivers slowed as are much different from those that existed in the late they approached the sea, dropping much of their Triassic. It is important to review these profound load of suspended silt and mud and building up events carefully, because they had an extremely broad mud flats in the process. The mudflats and the important consequence: collectively the geologic river floodplains leading to them extended south- events of the middle Triassic created enormous east from the coastline across all of eastern Utah, Dawn of the Utah Mesozoic 29

Utah, it submerged the mudflats and floodplains, covering them with thin layers of limestone or other marine sediment. When the marine advance (known as a transgression) was over, the sea withdrew to the west. The withdrawal of the ocean from eastern Utah (known as a regression) allowed river- deposited mud to bury the thin limestone deposited earlier. This cycle of coastal oscillation occurred several times, giving rise to a belt of complex interfingering between marine and nonmarine sediments in the early Triassic rock record of central Utah (fig. 2.6). Around Kanab, for example, the Moen- kopi Formation consists mostly of mudflat and floodplain deposits but also contains three portions deposited either under ocean water or close to the edge of the sea. These marine or marginal marine portions of the Moenkopi in this area are known as the Timpoweap, Virgin Limestone, and Shnabkaib Members. 2.5. The Utah region at the end of the early Triassic, In contrast to the richly fossiliferous oceanic about 245 million years ago. Reconstruction from rocks of western Utah, the early Triassic nonma- Ronald Blakey/Colorado Plateau Geosystems, Inc. Used with permission. rine strata of eastern Utah have produced far fewer fossils. Nonetheless, the scanty fossil evidence pre- even covering portions of modern-day Colorado, served in the Moenkopi Formation suggests that Arizona, New Mexico, and Wyoming. Up to 1,500 the mudflats and swampy floodplains were popu- feet of fine-grained silt, locally mixed with sand and lated by a variety of terrestrial and semiaquatic ver- clay, accumulated on these expansive mudflats and tebrates. Not surprisingly, given the abundance of floodplains. These sediments are now known as the water in these habitats, amphibians dominate the Moenkopi Formation in southern Utah (fig. 2.6) scanty Moenkopi vertebrate fauna. Several different and the Four Corners area, the Ankareh Formation types of flat-headed amphibians have been identi- in the Wasatch Mountain region, and the Popo Agie fied, some of them fairly large. Fragmentary remains Formation of Wyoming and Idaho. Emulating Trias- of terrestrial reptiles also have been discovered in sic rocks elsewhere in the world, the Moenkopi and the Moenkopi, but their abundance pales in com- contemporaneous rocks are thoroughly stained red parison with the much more common amphibians. by the oxidation (“rusting”) of iron-bearing mineral One of the best-known reptiles is Arizonasau- grains. The Triassic “age of red beds” begins with the rus, a 10-foot-long (3.3-meter) quadrupedal preda- deposition of the Moenkopi Formation and time- tor with a large sail-like fin along its back (Nesbitt equivalent units west of the early Triassic shoreline. 2003). Arizonasaurus was not a dinosaur but was The low relief of the central Utah coastline, cou- still well adapted for life on land and appears to pled with strong climatic shifts that induced tem- have been an efficient predator of smaller reptiles porary changes in the level of the sea, caused the and amphibians. Arizonasaurus probably represents early Triassic shoreline to migrate east and west sev- a group of advanced pseudosuchian reptiles known eral times. Each time the sea penetrated into eastern as the Rauisuchia (fig. 2.2) and illustrates the strong 30 Chapter 2

2.6. The Moenkopi Formation near Goblin Valley. Red mudstone and tan sandstone in the fore- ground represent the Moenkopi Formation. Several formations of the overlying Glen Canyon Group are exposed in the cliffs beyond. Courtesy John Telford. evolutionary trend among Triassic reptiles toward Scant vertebrate fossils from the Moenkopi For- efficient movement on land and a predatory diet. mation are supplemented by another source of Numerous other pseudosuchians and related rep- information on the nature of land life in Utah dur- tiles were competing with Arizonasaurus for success ing the early Triassic. Footprints and trackways of as land predators. We have no evidence that dino- terrestrial animals are very common in the mud- saurs played a major role in the terrestrial ecosys- stones and siltstones of the Moenkopi Formation. tem at the time when the Moenkopi sediments were The sticky mud that was deposited along the low accumulating in the Utah region. coastal plain evidently served as a perfect medium Dawn of the Utah Mesozoic 31 for the preservation of footprints made by animals of Laurasia started to move against and over the sea- moving across the landscape. Some spectacular floor to the west. The geological serenity that pre- early Triassic trackway sites have been discovered in vailed in western Northern America during the late the Colorado Plateau region. These footprints have stages of Pangaea was replaced by compressional been intensively studied by paleontologists in recent forces that caused uplift of the earth’s crust through- years. While some are clearly reptilian in form, none out the Great Basin and Rocky Mountain regions. of them can be confidently attributed to dinosaurs. No major mountain ranges were elevated during the The Moenkopi-age tracks in the Colorado Plateau Triassic period, but many areas began to rise as the seem to have been made by a variety of nondino- immense compressional forces started to warp the saurian reptiles such as rauisuchids, ornithosuchids, crust upward. lizards, and therapsids. One such uplift was a gentle arch that emerged Combining the evidence from both footprints in eastern Nevada and western Utah, referred to by and body fossils, it appears that dinosaurs were W. L. Stokes (1986) as the Mesocordilleran High. very rare if present at all in the Utah region dur- The lifting of the Mesocordilleran High raised the ing the early Triassic, although a diverse reptile ancient seafloor of western Utah and caused the and amphibian fauna existed. This may be because withdrawal of the early Triassic seas from most of the swampy environment favored the amphibi- the Great Basin, including western Utah (fig. 2.7). ans or perhaps because remains of whatever dino- The west coast of North America stepped to the saurs might have been present by chance were not west as the early Triassic seafloor emerged in the preserved. Whatever the reason, the nonmarine vertebrate fossils and tracks from the Moenkopi Formation offer no evidence that the age of dinosaurs had begun in Utah in early Triassic time. No solid, indisputable evidence of dinosaurs has ever been discovered in rocks of this age.

The Late Triassic: A Time of Change

During the middle portion of the Triassic the geological setting of Utah began to change in ways that were extremely important in creating the Mesozoic wonderland in the eastern part of the state. Laura- sia, carrying North America with it, began to separate from the rest of Pangaea as rifting and volcanic activity intensified along what is now the northern Atlantic seaboard. The North American region was carried to the northwest as a rift valley opened within Laurasia that would eventually develop into the modern Atlantic Ocean basin. Although the western part of the embryonic North Ameri- 2.7. The Utah region in late Triassic time, about 220 million years ago. The highland in central Nevada is known can continent was not directly affected by the rift- as the Mesocordilleran High. Reconstruction from ing, it did begin to yield to the compressive forces Ronald Blakey/Colorado Plateau Geosystems, Inc. that were generated as the North American portion Used with permission. 32 Chapter 2

Great Basin region, and hundreds of miles of new surface that was produced during this period of land appeared where the ocean formerly had been. erosion and/or nondeposition. Such a surface is With the Mesocordilleran High serving as a barrier known as an unconformity, a break in the geologi- between Utah and the proto–Pacific Ocean, the geo- cal record (fig. 2.8). All unconformities represent a graphic setting changed from a coastal scene to an gap in our chronological record of land and life. It interior basin. The seas did briefly return to Utah is difficult to tell exactly how much time is repre- in later times (as we’ll see in chapters to come), but sented by the unconformity at the top of the Moen- they came from the north or south. Once the Meso- kopi Formation. A good guess is that it signifies a cordilleran High developed, it forever prevented the hiatus of approximately 15 million years. When the seas to the west from submerging any part of Utah. deposition of sediment resumed in the later Triassic, The compression that lifted the Mesocordille- the local environment had changed considerably— ran High was the result of tectonic plates moving and so had the creatures it sustained, much to the in opposite directions: the North America plate, a delight of dinosaur lovers! west-moving fragment of Laurasia, was sliding over one or more oceanic plates that were moving east- The Chinle Formation: The Age of Dinosaurs Begins ward. The oceanic plates sliding beneath western North America were bent and forced downward With the emergence of the Mesocordilleran High in under the over-riding continent in a process known western Utah and eastern Nevada in middle Triassic as subduction. This action eventually resulted in time, the landscapes of east-central Utah were dra- the generation of molten rock beneath the over-rid- matically changed. The low coastal plain that existed ing plate carrying North America. The molten rock during the time when the Moenkopi Formation was (magma) that formed from this melting eventually being deposited was transformed into an interior rose through the crust above to be erupted as lava basin surrounded by higher terrain on at least three or to be emplaced as masses of rock similar to gran- sides (fig. 2.7). To the west and southwest of this ite if it cooled before it reached the surface. Trias- basin rose the slopes of the Mesocordilleran High, sic volcanic and granitic rocks are fairly common in while highlands of presumed volcanic origin in cen- western North America, whereas they are very rare tral Arizona formed the southern margin of the in earlier periods. The igneous activity, the crustal basin. In addition, judging from the patterns of sed- uplift, and the mountain-building that began in the iment dispersal during late Triassic time, it appears Triassic intensified throughout the West in later that a hilly terrain existed in central Colorado, rep- phases of the Mesozoic. As we shall see, the geo- resenting the eroded roots of the Ancestral Rocky logical convulsions of the mid-Triassic are just the Mountains, which had been uplifted during the late beginning of processes that dominated the Meso- Paleozoic. This interior basin seems to have been zoic history of Utah and adjacent regions. open to the northwest. The high lands surround- As these great changes were underway, the depo- ing the basin on the east, south, and west served as sition of mud and sand in central Utah apparently watersheds, capturing moisture from the late Tri- was suspended for a time. Responding to the ris- assic storms. As the water from the marginal high- ing land in western Utah, the rivers that deposited lands descended toward the center of the basin, it the Moenkopi sediments either shifted their courses collected into larger streams that eventually flowed or began to erode some of the sediment that they northwest, out of the basin toward the sea in what had previously spread out across the Colorado Pla- is now Nevada and Oregon. This large stream has teau. Everywhere in the Colorado Plateau the top of been named the Chinle Trunk River, after the term the Moenkopi Formation is marked by an irregular used to describe the sediments it deposited in the Dawn of the Utah Mesozoic 33

2.8. The Triassic strata of Utah. Vertical ruling indicates gaps (unconformities) in the sequence of rock layers.

Colorado Plateau region (Riggs and others 1996). All of the sediments in the Chinle Formation The Chinle Trunk stream, along with numerous were deposited in nonmarine settings such as lakes, tributaries that flowed into it, spread gravel, sand, stream channels, river floodplains, and swamps. and mud across the broad floor of the interior basin Scattered throughout this heterogeneous assem- of south-central Utah. blage of sediments are numerous thin layers of vol- The surface of the basin was nearly flat, and some canic ash. The ash was commonly altered into a of the sluggish rivers emptied into lakes that dot- clay mineral known as bentonite and reworked ted the floodplains. The volcanic activity in adjacent into the fine silt deposited in ponds or floodplains regions periodically produced clouds of ash that to produce bentonitic mudstones. When the soft drifted over the basin to settle out in layers across ash or bentonite is exposed at the surface, oxida- the low plain. The assemblage of sediment that doc- tion of metals in the volcanic materials produces uments the existence of this interior basin is thus a shades of purple, brown, yellow, and lavender. The complex mixture of conglomerate, sandstone, mud- poorly lithified sediment is rapidly eroded by water stone, and volcanic ash. Named for a small outpost and wind to produce a gullied landscape, the clas- on the Navajo Reservation of northern Arizona, the sic “badlands” of western lore. Some of the most Chinle Formation reveals the beginning of the age scenic landscapes in the world develop from the of dinosaurs in the Utah region. weathering and erosion of the Chinle Formation. 34 Chapter 2

2.9. Outcrops of the colorful Chinle Formation near Capitol Reef National Park in central Utah. Photo by Frank DeCourten.

The soft pastel-banded hills and colorful bad- to the Chinle Formation (or Group) is a somewhat lands of the Painted Desert of northern Arizona are confusing tangle of names that vary from place to named for the distinctive colors of the Chinle bad- place. This is not surprising, though, because the lands exposed in that area. Similar exposures of the sedimentary rocks of this unit were deposited in Chinle Formation can be found in many places in exclusively nonmarine environments that had lim- southern and southeast Utah (fig. 2.9). ited lateral extent and shifted continuously through Geologists have developed different ways of sub- late Triassic time. The stratigraphic nomenclature dividing the complex and regionally variable stra- of the Chinle Formation is complex because of the tigraphy of the Chinle Formation. Several different extreme variability of sediments that it contains. We members have been established within the forma- will see a similarly complex pattern in other Meso- tion. In Utah the most important subdivisions are zoic rock units of the Colorado Plateau in later the Shinarump, Petrified Forest, Mossback, Owl chapters. Recall from chapter 1 that this pattern of Rock, and Church Rock Members (fig. 2.7). Other lateral variability is a normal feature of sedimentary members have been recognized in adjacent portions rocks deposited by river systems. For the purposes of the Colorado Plateau (Arizona and New Mex- of our review of the Chinle rocks and fossils, we will ico). Some scientists (e.g., Lucas, 1991a, 1991b) have use the traditional subdivisions (members) of the suggested that the Chinle should be elevated to the Chinle Formation, though these terms may be con- rank of a group consisting of several distinct for- sidered formations by other scientists. mations. Consequently the nomenclature applied Dawn of the Utah Mesozoic 35

Resting above the unconformity marking the represent sediment that accumulated on the flood- top of the Moenkopi Formation throughout most plains adjacent to the larger stream courses. Units of southeastern Utah is a layer of conglomerate and deposited primarily on floodplains include the coarse sandstone up to several hundred feet thick. Church Rock Member or Rock Point Formation of This gravelly material at the base of Chinle is known the Chinle Group. Other units within the Chinle as the Shinarump Conglomerate. Most geologists sequence consist of a mixture of lake-bed clays, consider it to be the first subdivision of the Chinle river-channel sands and gravel, and floodplain silt. Formation (or Group). The Shinarump Conglomer- The Monitor Butte Member/Formation and Owl ate was deposited by swift rivers flowing toward the Rock Member/Formation are examples of such het- northeast across southern Utah. As the rivers con- erogeneous units. Finally, other subdivisions of the stantly shifted their courses back and forth across Chinle (such as the Mossback and Cameron Mem- the lowlands of southern and eastern Utah, a broad bers/Formations) represent relatively coarse-grained sheet of coarse deposits was formed. The sand and sands and gravel that accumulated in the channel gravel of the Shinarump is usually well cemented of the larger rivers, much like the Shinarump Mem- and commonly forms a hard “cap” that protects the ber. The Chinle Formation is thus a complex assem- softer sediment of the underlying Moenkopi For- blage of sediments deposited in a variety of specific mation from the ravages of erosion. Many of the setting across the lower interior basin of late Trias- mesas and benches of southern Utah have lower sic time. slopes of soft red rock that ascend to a horizontal caprock of Shinarump Conglomerate. Hurricane Nondinosaur Fossils of the Chinle Formation: A Rich Mesa, near Zion National Park, and the Mummy Ecosystem Revealed Cliffs near Torrey (fig. 1.1) are good examples of this phenomenon. In contrast to the sparse assemblage of fossils pre- Above the Shinarump Conglomerate are other served in the underlying Moenkopi Formation, units that record different conditions of sediment fossils occur in amazing abundance in the Chinle deposition. The Petrified Forest Member (or For- sediments. The list of fossils from the Chinle beds is mation), for example, consists of variegated red, a long one indeed, including plants, invertebrates, green, and purple siltstone and mudstone that con- footprints, and vertebrate material. The various dep- tains abundant bentonite. Most of this fine-grained ositional environments in which Chinle sediments material accumulated in swamps and lakes that accumulated all had relatively high potential for developed on the low and poorly drained floor of preserving fossils of the organisms harbored there. the interior basin in Utah and adjacent states. The The fossil plants from the Chinle Formation are fine grains of silt were primarily derived from the so spectacularly abundant in places that in 1962 the south, but the volcanic ash represented by the ben- Petrified Forest National Park in northeast Arizona tonite probably drifted in from the west, where was established to protect the great number of enor- there is good evidence for volcanic activity during mous fossil logs weathering out of the soft pastel the late Triassic. Some units within the Chinle For- mudstones. Elsewhere in the Colorado Plateau fos- mation (Group) consist of reddish-brown to pur- sil plant material is commonly found in exposures ple siltstone and fine sandstone that lacks bentonite of the Chinle Formation, though nowhere else do and contains small grains of mica and quartz. These the abundance and preservation rival the national red beds commonly exhibit sedimentary structures park. Fossil plants from Chinle sediments in Utah produced by flowing water, such as ripple marks occur in notable abundance in areas around the Cir- and cross-bedding. Most of the Chinle red beds cle Cliffs near Capitol Reef National Park (fig. 2.10) 36 Chapter 2

2.10. Fossilized trunks of ancient trees belonging to the genus Araucarioxylon weathering out of the Chinle Formation near Capitol Reef National Park. Person in the background for scale. Photo by Frank DeCourten. and in the San Rafael Swell. More than fifty different One major group of plants that is not represented kinds of plants have been identified from the Chinle in the Chinle flora is the flowering plants (angio- Formation, including fungi, lycopods (relatives sperms). These plants, with their flowers and seed- of the club mosses), ferns, conifers, ginkgoes, and bearing fruit, dominate the modern global flora cycads. The large trees preserved at Petrified Forest but did not appear until the late Cretaceous. Thus National Park and elsewhere are mostly the remains the forests of the Chinle basin were lush and dense of Araucarioxylon, a large conifer. Preserved logs of but consisted of an aggregation of relatively prim- Araucarioxylon up to 7 feet (2.3 meters) in diameter itive types of plants. Researchers have concluded and over 120 feet (40 meters) long have been found. from the character of the flora and other factors that Even such large fossil specimens are incomplete; the the climate nurturing these forests was warm and living tree must have been even larger, likely exceed- humid, at least during the early part of the time rep- ing 200 feet (about 65 meters) in height. The giant resented by the Chinle Formation. A stroll through conifers might have been the most impressive ele- the forest in late Triassic Utah might have been ment of the late Triassic flora in the Colorado Pla- similar to hiking through today’s rain forests in teau, but many other plants of lesser stature were the Amazon Basin, although the prehistoric forest growing in their shadows. Ferns and horsetails car- had no flowers or fruit. Near the end of the Trias- peted the forest floor, while cycads similar to the sic period, during the time represented by the upper modern “sego palms” and ginkgoes stood a bit Petrified Forest Member, the Chinle forests appear higher as shrubs. to have became a bit more open. A general trend Dawn of the Utah Mesozoic 37

2.11. Fossil fish from the Chinle Formation of Utah: A. Cionichthys, a bottom-feeding fish known from San Juan County; B. Hemicalypterus, a deep-bodied browser that probably fed on aquatic plants and algae; C. Ceratodus, an omnivorous lungfish that lived in the shallow streams and rivers of Late Triassic Utah. Note the scale bars for size. After Colbert 1972. toward a drier and more strongly seasonal climate dry conditions, perhaps on a seasonal basis. The late seems to have somewhat limited the density of the Triassic fish fed on plants, molluscs, and other fish plant growth, producing a more open woodland. populating the sluggish rivers of the Chinle basin. For most of the late Triassic the lowland basin of In addition to the fossil fish, a diverse array of southeast Utah was without doubt a well-watered semiaquatic vertebrates has also been recovered terrain. The basin was laced by rivers and dotted from the Chinle Formation in the Colorado Pla- with lakes and ponds. Not surprisingly, then, the teau region. Several different amphibians are known Chinle Formation produces a diverse fossil fauna from the Chinle strata, of which the most common dominated by aquatic forms. The fossils of freshwa- and best known is Metoposaurus. This amphibian ter bivalves and the burrows of crustaceans (cray- had an almost comical appearance, with a huge flat- fish) are fairly common in some portions of the tened spadelike head and laughably small legs on Chinle Formation. In addition, many kinds of fossil a body some 6 feet (2 meters) long (fig. 2.3A). Lin- fish have been discovered from localities throughout ing the jaws of Metoposaurus were many sharp- the Colorado Plateau. Around Zion National Park pointed teeth, clearly indicating the predatory habits and in the Lisbon Valley area of San Juan County, of this amphibian. Metoposaurus and other similar the Chinle sediments have produced specimens of amphibians probably spent most of their lives in the Cionichthys, Hemicalypterus, Ceratodus, and several rivers, lakes, and ponds of the Chinle basin, lying in other species of fish (fig. 2.11). Among the fish, Cer- wait on the bottom for any unwary prey that ven- atodus is particularly interesting because it belongs tured within reach of their “fish-trap” jaws. Met- to the order Dipnoi, which includes a close rela- oposaurus and its kin (the metoposaurids) would tive: the living Australian lungfish. Lungfish are spe- have been extremely clumsy on dry land and prob- cifically adapted to life in ephemeral streams that ably never traveled far from the water’s edge. Less periodically dry up. During droughts the lungfish common amphibians from the Chinle include burrow into the drying mud, seal the cavity with Buettneria and Apachesaurus. mucous, and wait for the waters to flow again. The In addition to the fish and amphibians, other ver- presence of lungfish in the Chinle Formation sug- tebrates swam in the Chinle streams and lakes. In gests that the climate alternated between humid and many localities where fossils have been found in 38 Chapter 2 the Chinle beds, phytosaurs are the most common diet. Several genera of phytosaurs are known from of all vertebrates. The phytosaurs (fig. 2.3B) looked late Triassic strata in the Colorado Plateau region, much like a modern crocodile, but the resem- among which the best known are Rutiodon and the blance was only superficial. Phytosaurs are placed classic Phytosaurus. Although the phytosaurs were in a different category (usually the family Phytosau- similar to crocodiles in their ecological habits and ria or the Parasuchidae) than modern crocodiles general appearance, it is important to bear in mind and alligators (the order Crocodilia) because they that they are not closely related to the modern croc- are distinguished from them by some unique ana- odiles. The earliest true crocodiles did appear in the tomical features. Most notably, the phytosaurs have late Triassic, but these creatures were rather small, the external nostrils positioned on a small mound lizardlike animals. The similarity between the phy- between and slightly in front of the eyes. Crocodiles tosaurs and the modern crocodiles is a good exam- have nostrils located at the tip of the snout, also on ple of convergent evolution, the development of a slightly raised bony platform. Because their nos- similar characteristics by two unrelated groups of trils are on the snout, crocodiles have a bony palate animals through their adaptation to similar habitats on the roof of the mouth that separates the air- and ecological niches. For some reason phytosaurs way from the normally water-filled mouth cavity. are relatively rare in Utah outcrops of the Chinle This nasal architecture allows crocodiles to breath Formation. Elsewhere in western North America— while they swim and float mostly submerged, with in Texas, Arizona, New Mexico, and Wyoming— just their nostrils and eyes above water. The phy- phytosaurs are among the most common vertebrate tosaurs could likewise remain mostly submerged, fossils in rocks of Chinle age. breathing through the nostrils located on the top of In addition to the aquatic and semiaquatic ver- the head. In phytosaurs air flowed directly from the tebrates, the Chinle and equivalent late Triassic nostrils downward into the throat without traveling strata have produced the remains of a great vari- the length of the snout. Hence phytosaurs did not ety of reptiles that were better adapted to dry land possess the secondary bony palate that crocodiles or “upland” habitats. Among this group are the aet- have. To enhance their swimming abilities, the bod- osaurs and the dicynodonts. The aetosaurs (sub- ies of both phytosaurs and crocodiles are long and order Aetosauria, family Stagnonlepididae) were streamlined, with broad, flexible tails designed to herbivorous reptiles that looked somewhat like a swing laterally in a serpentine fashion. plant-eating crocodile (fig. 2.3C). The most distinc- The bodies of phytosaurs were up to 20 feet tive feature of the aetosaurs was their heavy armor, (6.5 meters) or more in length and armored with consisting of an impenetrable pavement of bony more or less rectangular plates of bone (scutes) plates that covered the back, tail, and flanks of these embedded in the skin, much like a modern croc- reptiles. In addition, the aetosaurs had large spikes odile. With their short and stubby legs, phyto- extending from the shoulder and neck region, saurs appear to have spent most of their time in the tapering posteriorly to blunt nodes along the flanks. water, where they must have been the top predator. The heads of aetosaurs were relatively small, and The teeth of phytosaurs are of several types, vary- their jaws were lined with diminutive weak teeth. ing from sharply pointed and conical to bladelike The aetosaurs seem to have been only slightly bet- in form, clearly designed to capture a mobile prey ter suited for crawling on dry land than were the animal. Phytosaurs probably consumed anything phytosaurs. They probably lived mostly along river- that they could catch or find, just as modern croc- banks and lakeshores, where soft vegetation on low- odiles do. Fish, amphibians, and other unwary rep- growing shrubs was available in abundance. Of the tiles constituted the main portion of the phytosaur’s several genera of aetosaurs known from the Chinle Dawn of the Utah Mesozoic 39

Formation, the most common are Desmatosuchus dozens of different types of reptiles and amphibi- and Typothorax. ans, each adapted for a specific habitat and ecologic The dicynodonts are mammal-like reptiles (order niche. The scene had changed dramatically from the Therapsida) that resembled a reptilian version of relatively barren coastal plain of Moenkopi time. By a pig. For example, Placerias, the most common the late Triassic the overall conditions in the interior Chinle dicynodont, was 3–5 feet (1–2 meters) long basin of central Utah seem to have been optimal and rather bulky, with short legs and a large head for reptiles. A warm, humid climate supported a (fig. 2.3D). Placerias had two large tusks that pro- lush tropical forest that provided the perfect habitat jected down and outward from the upper jaw. The for a varied reptilian fauna. In spite of its astonish- jaws of this strange dicynodont had no other teeth. ing richness of the late Triassic fauna, we have yet to Instead the snout was tipped by a curved beak with explore the most fascinating element. The adaptive sharp edges of bone along the jaws, similar to the radiation of reptiles in the Triassic also produced rostrum of a turtle. Placerias probably ate tough, a group of bipedal carnivores that were to domi- low-growing vegetation. The prominent tusks of nate the terrestrial ecosystem in the coming geo- these dicynodonts were likely used for a variety logic periods. The colorful Chinle strata provide our of tasks, including rooting and digging for food, first glimpse of these creatures, almost lost among defending against predators, and sparring with the complicated mosaic of amphibians, phytosaurs, members of their own species for mates. Placerias aetosaurs, and dicynodonts. In the Colorado Pla- was a fully terrestrial animal and probably foraged teau the age of dinosaurs begins in the late Triassic. through the lush late Triassic forests a considerable We find the first hint of dinosaurs in the Southwest distance from water. among the Chinle fauna. In addition to the animals already described, the “upland” fauna of the Chinle Formation included Traces of Dinosaurs of the Chinle Formation other reptiles that are less common or are known only from very fragmentary material. Hesperosu- Some of the evidence for the earliest dinosaurs in chus (fig. 2.3F) was a 4-foot-long (1.3-meter) bipedal the Utah region comes from the study of reptile pseudosuchian that was a very agile and active footprints and trackways preserved in the strata of predator, consuming insects and small lizards. In the Chinle Formation. No fossil bones that indis- New Mexico, Arizona, and Wyoming fossils of sev- putably belong to late Triassic dinosaurs currently eral different quadrupedal and predatory rauisu- have been described from exposures of the Chinle chians and lizardlike “rhyncosaurs” have also been in Utah. As we will see, bones representing several discovered in Chinle-equivalent rock units. None of different dinosaurs are known from Chinle sedi- these miscellaneous reptiles have yet been discov- ments in nearby areas; but the footprints in this for- ered from the late Triassic rocks of Utah; but they mation first announce the emergence of dinosaurs are known from surrounding areas, so it is likely in Utah. It is probably only a matter of time and fur- that they lived everywhere on the floor of the Chinle ther exploration before we find the fossil remains of basin. These and many other types of reptiles cer- the track-makers, but for now all that we have are tainly await discovery in the Utah exposures of the the footprints. Exactly what can a footprint or track Chinle Formation. preserved in rock tell us about Utah’s first dino- The vertebrates that we have thus far reviewed saurs? Plenty! make up a rich and diverse assemblage consisting of Footprints and trackways of terrestrial animals aquatic and terrestrial forms. The low forested basin are fairly common in upper portions of the Chinle of Chinle time in Utah was literally crawling with sequence such as the Church Rock Member or Rock 40 Chapter 2

Point Formation (Lockley and Hunt 1995). In the past decade or so the study of tracks and footprints preserved in Triassic sediments has produced many new and important insights on the earliest dinosaurs of western North America (e.g., Hunt and Lucas 2007). Researchers have discovered, documented, mapped, and analyzed literally hundreds of track-bearing rock sequences in Colorado, New Mexico, Arizona, Utah, and other western states. Vertebrate footprints are known from numerous places in the Chinle sediments of Utah, but three localities stand out as especially revealing for our purposes: the area around Dinosaur National Mon- ument, Shay Canyon north of Monticello, and along the northern shore of Lake Powell (for full descriptions of these sites, see Lockley and Hunt 1995; Hunt and Lucas 2007; and the many references cited therein). Paleontologists have traditionally assigned lati- nized names to footprints in a manner similar to the naming of body fossils. The names are useful because the overall morphology of each distinctive track (such as its size, length and number of digits, shape of the toes) can be summarized with a 2.12. Late Triassic dinosaur tracks from the Chinle For- single term, known as an ichnogenus, which may mation of Utah: A. Grallator track, attributed to a bipedal include morphological variants known as an ich- carnivore, perhaps a theropod dinosaur; B. Atreipus, a nospecies. It is important to bear in mind that it is track from the Chinle beds near Lake Powell (note the small forefoot or manus imprint and the blunt claw usually impossible to relate any ichnogenus or ich- marks on the hind foot impression: these features may nospecies to a specific track-making animal with indicate the presence of a quadrupedal and herbivorous absolute certainty. We can only make inferences ornithischian dinosaur); C. a large track from the Shay on the identity of the track-maker by comparing Canyon locality likely made by a theropod dinosaur; D. Tetrasauropus-like track from the Dinosaur National the foot anatomy of known prehistoric creatures Monument area. Tracks of this type that show forefoot with the pattern that characterizes the various ich- and hind foot impressions may have been made by pro- nogenera and ichnospecies. In many cases a sin gle sauropod dinosaurs. Scale bar = 2 inches (5 cm) in all sketches. After Lockley and Hunt 1995. type of track (a specific ichnogenus) may have been made by several different animals. Similarly a single animal may leave several different types of the Chinle in Utah, where body fossils are rela- tracks, depending on its size, age, speed of locomo- tively rare. tion, posture, and the type of substrate it walked Late Triassic footprints and trackways have been on. Nonetheless, tracks preserved in rock can pro- discovered at more than thirty-five sites in the vicin- vide valuable information on the overall composi- ity of Dinosaur National Monument (Lockley and tion and nature of the terrestrial vertebrate fauna. Hunt 1995). Among these tracks is the ichnogenus This is particularly true in rock sequences such as Grallator, a three-toed track up to several inches in Dawn of the Utah Mesozoic 41 length that almost certainly was made by a bipedal made by different dinosaurs; both were probably dinosaur (fig. 2.12A). With the sharp claw marks early bipedal theropods. that terminate each of the three toe marks, Grallator Tracks resembling Atreipus also have been dis- most likely represents a small theropod dinosaur. covered in the upper Chinle Formation along the In addition, researchers have recorded the tracks of shores of Lake Powell, but they vary slightly from a large quadrupedal animal that had smaller fore- the classic form of this ichnogenus: they com- limbs than hind limbs (fig. 2.12B). These rounded monly lack the sharp claw marks on the tips of tracks, about 8–10 inches (20–25 centimeters) in the toe impressions. In addition, many of the large diameter, appear to be similar to sauropod tracks Atreipus-like tracks from Lake Powell are associ- from the Jurassic and Cretaceous, but they are ated with much smaller footprints that may rep- smaller and have somewhat less distinct toe impres- resent the forefoot (or manus) of a quadrupedal sions. These tracks may belong to the similar ich- rather than bipedal reptile (fig. 2.12B). Moreover, the nogenus Tetrasauropus (fig. 2.12D), considered to Lake Powell tracks are smaller than the Shay Can- be the footprints of a prosauropod dinosaur. Asso- yon tracks, reaching lengths of only about 5 inches ciated with the theropod and possible prosauropod (12 centimeters) (Lockley and Hunt 1995). We are tracks in the Dinosaur National Monument area are still not sure what dinosaur might have made the other ichnogenera most likely made by primitive Atreipus-like tracks at the Lake Powell site. It may sphenodontid lizards (Rhynosaurpoides), aetosaurs have been an early ornithopod dinosaur or, alter- (Brachychirotherium), and mammal-like reptiles. nately, an unknown quadrupedal theropod. In any To the south, in Shay Canyon and around case these odd tracks provide evidence of more than Lake Powell, horizons in the upper portion of the a single type of dinosaur inhabiting the interior Chinle Formation have produced tracks preserved basin during late Chinle time. in sandstone and mudstone of the Church Rock The footprint record of the Chinle strata in Utah Member (or Rock Point sequence). Once again, attests to a diverse population of reptiles during the tracks made by nondinosaur reptiles are common late Triassic. The three-toed tracks are most prob- at these localities, including the ichnogenera ably the traces of dinosaurs because (as summa- Brachychirotherium and Pentasauropus, the latter rized in the appendix) the reduction of digits in the most likely made by a dicynodont reptile similar to hands and feet from the primitive pattern of five is Placerias. Some of the tracks, however, appear very the hallmark of the Dinosauria and not a common likely to have been made by dinosaurs. Three-toed trait in other reptile groups. While many footprints tracks, similar to the ichnogenus Atreipus, have are also known from the underlying Moenkopi For- been observed at both localities (Lockley and Hunt mation of early Triassic age, none of them show 1995). The Atreipus-like tracks are more or less sim- the advanced foot morphology that characterizes ilar to the Grallator tracks described earlier but the dinosaurs. Thus the Age of Dinosaurs begins are very large at Shay Canyon, reaching lengths of in Utah during the time represented by the Chinle nearly 8 inches (20 centimeters) (fig. 2.12C). What Formation. could be considered the “heels” of Grallator and Most scientists estimate that the Chinle Forma- Atreipus actually represent the “balls” of the foot tion or Group encompasses the interval from about of the digitigrade track-makers and exhibit slightly 228 to 205 million years ago. On the basis of the different patterns. In addition, the impressions of footprint evidence, we can conclude that several dif- the pads on the underside of the toes are differ- ferent kinds of dinosaurs were probably ambling ent in the two ichnogenera. These considerations around the interior basin of central Utah where the suggest that Grallator and Atreipus tracks were Chinle sediments were being deposited. These first 42 Chapter 2 dinosaurs shared their lush habitat with a great vari- 2005; Nesbitt, Irmis, and others 2009). To this day ety of reptiles, fish, and amphibians. Dinosaurs were Coelophysis remains the best-known dinosaur from present on the Chinle landscape, but they were not the Late Triassic of the Colorado Plateau region, yet the dominant terrestrial vertebrates. They were although we now know that it shared its late Triassic in fact relatively rare in comparison to the abundant habitat with several other dinosaurs and scores of nondinosaur reptiles and amphibians. Unfortu- nondinosaur reptiles. nately, the Chinle deposits of Utah have not yet pro- Coelophysis was a small (7–8 feet [about 2.5 duced any fossils of the dinosaurs that may have left meters] long), delicate animal with long and slender the tracks preserved in the Chinle Formation; how- forelimbs ending in strongly clawed hands (fig. 2.13). ever, some good guesses about their identity can be The skull, positioned at the end of a highly flexible made by looking just beyond the borders of Utah, neck, is low and lightly built, with many small pierc- into New Mexico and Arizona. ing teeth positioned along the jaws. The hind limbs of Coelophysis are rather birdlike, with three functional toes on each foot. A fourth digit (actually the The Track-Makers: Chinle Dinosaurs “first” or the big toe) is present in the feet of Coe- of New Mexico and Arizona lophysis, but it is so reduced in size that it did not The Late Triassic Chinle interior basin extended reach the ground. Coelophysis probably subsisted on well beyond Utah into the surrounding portions a diet of insects, small amphibians, and lizards. This of the Colorado Plateau in northwest New Mex- dinosaur belongs to the Ceratosauria, those “prim- ico and northern Arizona. Fluvial (river-deposited) itive” theropods that lack many of the refinements and lacustrine (lake-deposited) sediments accumu- developed by later and more advanced predators lated in these areas during the same time when the (the Tetanurae). The validity of the name Coelo- Chinle sediments were being laid down in Utah. physis for the most common Chinle dinosaur has The general environments in Arizona and New recently been challenged by some paleontologists Mexico were similar to those already described for for reasons that have to do with the protocols used Utah in the late Triassic, but the specific pattern of to assign formal names to organisms (Heckert and sediment deposition varied somewhat, leading geol- others 1994). An alternate name, Rioarribasaurus, ogists to recognize different subdivisions (members has been proposed for this dinosaur; but most pale- or formations) of the Chinle sequence deposited ontologists have elected to use the traditional name near the margins of the basin. Coelophysis. Rioarribasaurus is mentioned here to The most famous Chinle vertebrate fossil local- avoid confusion for readers who might encoun- ity is the Ghost Ranch Quarry, located in Rio Arriba ter that name in other publications. Rioarribasaurus County, New Mexico, near the town of Abiquiu. and Coelophysis are the same animal. Excavations at this site, conducted primarily during Judging from the structure and size of the foot, 1947 and 1948 by Edwin H. Colbert of the American Coelophysis is an excellent candidate for consider- Museum of Natural History, have produced doz- ation as the progenitor of at least some of the tracks ens of skeletons of a small theropod dinosaur tra- preserved in Utah exposures of the Chinle Forma- ditionally known as Coelophysis, along with fossils tion. The size and morphology of the foot of Coe- of phytosaurs and other reptiles. Continuing work lophysis seem to be a pretty good match for the in the Chinle Formation at Ghost Ranch and at the general pattern of Grallator and Atreipus tracks. Petrified Forest National Park in Arizona over the Coelophysis has also been identified in the Chinle past decade has resulted in the identification of sev- Formation of northern Arizona, so we know that eral new late Triassic dinosaurs (Parker and Irmis this primitive theropod was widespread. It almost Dawn of the Utah Mesozoic 43

2.13. Coelophysis, from the Chinle Formation of New Mexico and Arizona, was a swift, lightly built predator, approximately 6 feet long. Based on reconstruction in Lucas 1994 (cited in chapter 8 references).

certainly lived in Utah, though we have not yet dis- predator appears to be quite primitive and may be covered any fossil evidence for its presence there. closer to the South American Herrerasaurus than In addition to Coelophysis, paleontologists have to the more highly evolved Chinle theropods. Also recently discovered evidence for other small thero- discovered in New Mexico along with Chindesau- pod dinosaurs in the Chinle Formation (e.g., Heck- rus were the partial remains of a very small bipedal ert and others 1994; Parker and others 2006; Nesbitt, predator named Dromomeron romerii (Nesbitt, Smith, and others 2009). Tawa hallae is known Irmis, and others 2009; Nesbitt, Smith, and oth- from several subadult skeletons excavated from ers 2009). This 3-foot-long (1-meter) reptile, known the Ghost Ranch area and is the best known of the mostly from bones of the hind limbs, probably rep- more recent discoveries from the Chinle Formation. resents a primitive ornithodiran reptile but can- Approximately 6 feet (3 meters) long, this small not confidently be placed in the dinosaur lineage. predator is quite similar to Coelophysis but some- In addition to these creatures, the Chinle sediments what more primitive in the structure and shape of have also produced fossils of reptiles that are very its upper jaws and snout. Like Coelophysis, Tawa dinosaurlike, though they are not in the same lin- probably fed on smaller reptiles, amphibians, and eage of archosaurs. The small, toothless, and bipedal fish. Though the several juvenile skeletons of Tawa predators known as Effigea and Shuvosaurus are known indicate a small animal, this theropod may examples of such reptiles that are not in the dino- have outgrown Coelophysis as an adult. The excel- saur lineage, despite their superficial similarities. lent preservation of the skeletal material of Tawa Thus Coelophysis and Tawa were clearly not the has allowed paleontologists to observe pockets in only bipedal predators inhabiting the Chinle land- the bones of the neck and back that housed air sacs scape, but they do firmly establish the presence in life. Such pneumatic pockets are characteristic of dinosaurs in the Utah region by about 215 mil- of the more highly evolved theropods of the Creta- lion years ago. But it would probably have been dif- ceous and clearly identify Tawa as an early member ficult to pick out these first dinosaurs among all of that lineage. the other similar groups of reptiles roaming the Chindesaurus was a somewhat larger bipedal the- Chinle basin. With so many predators and a lush ropod documented by several partial skeletons first flora thriving in the late Triassic, we might expect discovered at Petrified Forest National Park in Ari- to find the remains of many plant-eating reptiles zona (Long and Murry 1995) and subsequently as well, perhaps even herbivorous dinosaurs. Iso- found in New Mexico as well (Irmis, Nesbitt, and lated teeth of several different plant-eating reptiles others 2007). No complete skeletons of Chinde- have been discovered from Triassic strata in west- saurus have been recovered, but this theropodlike ern North America, but it is still unclear if these are 44 Chapter 2

Mexico as well as in Arizona. It almost certainly lived in Utah as well. When more complete remains of Revueltosaurus were found in Arizona (Parker and others 2005), however, it became clear that this creature belongs to the crocodilian clade and is not an ornithischian dinosaur after all. Another “ornithischian dinosaur” known as Tecovosaurus has been identified, once again on the basis of very small (about 0.1 inch [2–3 mm]) isolated teeth (fig. 2.14B), from late Triassic rocks in both Texas and Arizona. In addition, distinctive herbivore teeth with a highly enlarged cusp have been recovered from near the top of the Chinle-equivalent strata known as the Bull Canyon Formation in New Mexico. Accord- ing to the most recent assessments, none of these isolated teeth can be confidently identified as dinosaur remains; they are most likely the remains of some unknown archosaur herbivore (Irmis, Nesbitt, and others 2007). It remains unclear if any herbivorous dinosaurs lived in the Colorado Plateau region in the late Triassic, but there appear to have been numerous other kinds of plant-eating reptiles. This leaves unresolved the mystery of the animal that 2.14. The teeth of herbivorous reptiles from the Chinle made the Atreipus-like tracks of the Lake Powell Formation, New Mexico and Arizona: A. Revueltosau- region: perhaps it was an ornithischian dinosaur rus: note the large size of this tooth (bar = 0.2 inches [5 mm]); B. Tecovosaurus, known from Texas and New whose remains have yet to be discovered. Or maybe Mexico (bar = 0.4 inch [1 mm]); C. Lucianosaurus from some of the archosaurian herbivores were large New Mexico (bar = 0.4 inch [1 mm]). Redrawn from enough and had sufficiently specialized foot anat- Padian 1990 and Hunt and Lucas 1994. omy to have left the tracks. We clearly have much more to learn about the late Triassic dinosaurs of from plant-eating dinosaurs or other herbivorous Utah and can probably look forward to exciting dis- reptiles (fig. 2.14). The largest of these teeth belongs covering discoveries from Utah exposures of the to an herbivore named Revueltosaurus that was for- Chinle Formation. merly considered to be an ornithischian dinosaur (fig. 2.14A; Padian 1990). The teeth of Revueltosau- The Mid-Triassic Unconformity: A Frustrating Gap rus, about 17 mm (0.7 inch) long when complete, have flattened triangular crowns with small den- The new discoveries of dinosaur fossils in the ticles along the edges and are clearly not the teeth Chinle and age-equivalent strata clearly demon- of a carnivore. These teeth were designed to shred strate that several different types of dinosaurs had vegetation, and they exhibit wear facets along the become established in the Colorado Plateau region points of contact with opposing teeth. Revueltosau- in the Late Triassic. The dinosaurs were perhaps not rus was evidently widespread during the late Tri- the most dominant element of the terrestrial verte- assic, because its teeth have been found in New brate fauna, but they were certainly there between Dawn of the Utah Mesozoic 45

215 and 225 million years ago. Recall that no trace more than just two rock formations; it also divides of dinosaurs is found in the underlying Moenkopi Utah’s Triassic history into the early age of dinosaurs Formation, which represents deposits that formed (Chinle) and the predinosaur phase (Moenkopi). along the early Triassic coastal plain about 248–240 In between we have no information at all—just a million years ago. Where did the Chinle dinosaurs scoured surface of erosion between rock layers to come from? Did they originate in western North record the time when the dinosaurs first entered America, or were they immigrants from South Utah or evolved there. All we can be sure of is that America or elsewhere? Who were the ancestors of sometime between about 240 and 220 million years Coelophysis, Chindesaurus, and Tawa? Unfortu- ago dinosaurs joined the reptilian menagerie in the nately we have no answers to these questions. Fur- Colorado Plateau region. thermore, the mysteries are likely to persist for some By the end of the Triassic period several differ- time. The widespread mid-Triassic unconformity is ent types of dinosaurs were present in the Ameri- to blame for this. can Southwest. They were evidently evolving rapidly As noted, following the deposition of the Moen- in comparison to other groups of reptiles, becoming kopi Formation sediments, geological events began more dominant and larger as the Triassic drew to a to transform the low coastal plain of central Utah close. This late Triassic dinosaur fauna was a pros- into the interior basin of Late Triassic (Chinle) time. perous assemblage, living in what might be consid- Evidently, however, no sediments were deposited in ered a reptilian Garden of Eden. Then, about 210 Utah during the roughly 15 million years in which million years ago, just before the beginning of the the geological transition was taking place. This has Jurassic, a combination of geological and biological produced an extensive regional unconformity in events punctuated the evolutionary rhythm of these the Triassic rock record that separates the two for- early dinosaurs to set the stage for the next phase of mations throughout the Colorado Plateau region Mesozoic madness: the early Jurassic. (fig. 2.8). This mid-Triassic unconformity separates Chapter 3 The Early and Middle Jurassic 03A Time of Transition Near the close of the Triassic period some impor- The Late Triassic Extinctions tant changes began to affect the land and life of Paleontologists have long recognized that the transi- Utah. Even as the last layers of the Chinle Forma- tion from the Triassic to the Jurassic was marked by tion were being deposited, geological events were some significant changes in the character of life on in the process of ushering in a new landscape and a global scale. These changes were the result of the inducing profound changes in the climate of the extinction of many existing groups of organisms, fol- interior basin of the Colorado Plateau region. Pan- lowed by the adaptive radiation (a sort of evolution- gaea was beginning to show more obvious signs ary expansion) of the survivors and the emergence of of its fragmentation at the end of the Triassic than new groups of organisms near the end of the Triassic. it had earlier. The great Triassic rift valleys form- Intensive research on the Triassic-Jurassic event during along the eastern edge of North America deep- ing the past two decades has resulted in some new ened and began to divide that continent from the perceptions of the timing and pattern of the biotic Eurasian landmass. As cracks opened between the turnover (Benton 1991; Hallam 1991; Hesselbo and large fragments of Laurasia, at least 240,000 cubic others 2002). These events, in turn, have important miles of lava flooded onto what would become the consequences for understanding the history of dino- floor of the modern Atlantic Ocean. As it broke free saurs in western North America and elsewhere. from the rest of Laurasia, the core of North America The effects of the extinctions that occurred near migrated slowly to the northwest. The western edge the end of the Triassic period are evident in many of North America, where Utah was then located, led different groups of organisms that occupied a vari- the way, accelerated by the extra push toward the ety of habitats. In the seas the groups most strongly pole that resulted from the rifting occurring along impacted by extinction at this time included some the eastern continental margin (by today’s geogra- types of ammonites (the ceratites), many reef-build- phy). As North America moved north, it eventually ing organisms (sponges, bryozoans, and calcareous left the warm, moist tropics and entered the sub- algae), echinoderms (such as sea urchins and their tropical zone of dry climate that prevails at a lati- kin), and brachiopods. The bivalve molluscs (clams) tude of about 25 degrees north of the equator. As a were also affected, exhibiting a 90 percent reduc- consequence the climate of Utah became more arid tion in the numbers of species during the transition. at the end of Triassic time than it had been during Among marine and freshwater fish, a 33 percent earlier portions of that period. Even more profound decline has been documented near the end of the changes were taking place elsewhere in the world: Triassic (Benton 1989). The effects of the extinction the volcanic eruptions associated with the progres- event on terrestrial plants seem to have been simi- sive rifting of Pangaea discharged great volumes of larly dramatic, with approximately half of the preex-

CO2 in the atmosphere, rapidly warming the global tinction species disappearing over a period of about climate (Van de Schootbrugge and others 2008). 600,000 years.

46 The Early and Middle Jurassic 47

The pattern of the Triassic-Jurassic turnover Coelophysis. Although the early Jurassic record of among the terrestrial vertebrates, of course, is our dinosaurs is a bit sketchy in western North America, main concern, because the dinosaurs were pres- we do know that the quadrupedal prosauropods and ent both before and after the event. About half of sauropods were clearly present in the early Jurassic the families of Triassic terrestrial reptiles became (see below), though some sketchy evidence suggests extinct by the beginning of Jurassic time, about that they might have existed prior to the Triassic- 200 million years ago. The main victims of late Jurassic extinctions. In addition, within the thero- Triassic extinction in the terrestrial realm were pod lineage more specialized predators belonging several groups of pseudosuchian reptiles (nondi- to the ceratosaur group emerge in the early Jurassic, nosaur reptiles sometimes described as members such as the double-crested Dilophosaurus. Reason- of the Crurotarsi clade), including the rhyncosaurs, ably complete specimens of ornithischian dino- rauisuchians, ornithosuchians, phytosaurs, and saurs are also known from the early Jurassic strata mammal-like dicynodonts. Not all of these groups of western North America and include the armored died out at exactly the same time, but their num- Scutellosaurus along with other primitive types. The bers were sharply reduced in the late Triassic. By the evidence for such plant-eating dinosaurs in the late beginning of the succeeding Jurassic period they Triassic is very sketchy; even if present, they were had all disappeared from the fossil record. Taking not a prominent component of the fauna. the place of the groups that vanished during the Tri- As we will soon see, the fossils and trackways assic-Jurassic transition were both the survivors of preserved in early Jurassic rocks of the Colorado the extinction event and some newly evolved forms. Plateau region indicate not only a general increase The crocodiles, turtles, pterosaurs, and some sphen- in the size of dinosaurs but also an increase in the odontid reptiles were among the newcomers and diversity of the dinosaur communities. Even though all experienced a dramatic adaptive radiation in our knowledge of the dinosaur fauna of the early the Jurassic. In addition, the mammal-like reptiles Jurassic in Utah is limited by the scarcity of fos- became even more like mammals after the end of sils, we can clearly discern an obvious change as we the Triassic as the cynodonts and dicynodonts (such cross the boundary from the Triassic to the Juras- as Placerias) were replaced by a variety of crea- sic. It appears that the character of Utah’s dinosaur tures that seem to be much more advanced toward fauna shifted dramatically across the Triassic-Juras- “mammalness.” A great proliferation of mammalian sic boundary. What could have caused the great fau- groups including the morganucodonts, docodonts, nal turnover at the end of the Triassic period? and triconodonts (among many others) occurred The causes and timing of the Triassic-Juras- in the Jurassic. These creatures so closely resem- sic extinctions, and the subsequent faunal turn- ble primitive mammals that they can confidently be over, have been a controversial issue for many years considered the earliest members of that class. We among paleontologists. Recent analyses have uncov- no longer need to refer to these Jurassic beasts as ered evidence that the extinctions were relatively “mammal-like” reptiles, for they are clearly mem- rapid, perhaps occurring in less than 10,000 years bers of the early mammal lineage. (Ward and others 2004) and that they occurred What about the dinosaur faunas? How did at the very end of the Triassic, about 201 million they change across the Triassic-Jurassic bound- years ago. Moreover, the study of carbon (Hesselbo ary? Recall that dinosaurs were a minor compo- and others 2002; Van de Schootbrugge and oth- nent of the Chinle fauna in western North America ers 2008) and nitrogen isotopes (Paris and others and consisted of several small theropods similar to 2010) in the boundary sediments indicates some 48 Chapter 3 major disruptions of the carbon and nitrogen cycle that might be related to the great volcanic outburst at the end of Triassic time. N. R. Bonis and others (2010) suggest that the concentration of atmospheric CO2 during the Triassic-Jurassic extinctions could have been as high as 2,750 parts per million (ppm), compared to about 390 ppm today, which would have accelerated the warming trend dramatically. In addition, C. M. Belcher and others (2010) have attributed the sharp increase in the abundance of charcoal and soot in Triassic-Jurassic boundary sediments to intensified wildfires that reflect both changes in the character of the vegetation and climate-related factors such as aridity and lightning. Considerable geochemical evidence (e.g., Will- ford and others 2009; Richoz and others 2010) suggests that the deep circulation of the oceans was disrupted near the Triassic-Jurassic boundary, leading to a condition known as anoxia, when seawater becomes depleted in oxygen. 3.1. The great sand pile: The Glen Canyon Group of southern and eastern Utah. Thus it may be that the Triassic-Jurassic transformation of the global biota was caused by the The Early Jurassic Rock Sequence of Utah combination of several interrelated factors and perhaps others that we have yet to discover. We Almost everywhere in central and eastern Utah, the know that tectonic events were leading to rapid Chinle Formation is overlain by several formations changes in global geography, volcanic eruptions of early Jurassic age that consist dominantly of sand- were modifying the chemistry of the atmosphere stone. These formations represent the Glen Canyon and oceans, patterns of oceanic circulation were Group and include (in ascending order) the Wing- changing, and rapid climate change was under- ate Sandstone (and its lateral equivalent in south- way. If it was such interplay of factors that led to west Utah, the Moenave Formation), the Kayenta the extinctions, then we would expect the pat- Formation, and the Navajo Sandstone (fig. 3.1). This terns of biotic change to vary at different locations, threefold package of rock formations is usually easy at different times, and in terms of which groups to recognize in the canyon country of eastern Utah of organisms were affected. Such a complex pat- on the basis of the unique weathering profile of the tern of biotic turnover is precisely what the fossil three main components. The massive Wingate Sand- record is beginning to suggest for the end-Triassic stone typically erodes into magnificent sheer cliffs, event. To settle this question once and for all, we up to 400 feet high and often stained with black will need much more information on both the late streaks of desert varnish, that extend for miles as an Triassic and early Jurassic faunas than we currently unbroken wall. Comb Ridge, south of Monticello, is have. In any case the faunal change that accompa- an impressive exposure of the Wingate Sandstone nied the beginning of the Jurassic period brought (and other early Jurassic strata) that traverses more a whole new assemblage of dinosaurs to Utah and than 60 miles as a nearly continuous facade of solid adjacent regions. stone. The Kayenta Formation, resting above the The Early and Middle Jurassic 49

3.2. The Glen Canyon Group near Goblin Valley. The nearest cliffs are composed of the Wingate Sandstone. The ledgy beds at the top of these cliffs represent the Kayenta Formation, while the light-colored cliffs in the distance are exposures of the Navajo Sandstone. Courtesy John Telford.

Wingate Sandstone, is a heterogenous sequence of between them are eroded from the softer units. reddish-brown sandstone, siltstone, and mudstone Above the Kayenta slope an enormous wall of white of varying hardness. The Kayenta normally weath- to reddish sandstone towers to heights of well over ers into uneven slopes, broken by many small ledges 1,000 feet. This is the Navajo Sandstone, one of the and benches. The ledges mark the exposure of one most impressive cliff-forming rock sequences in of the harder layers of rock, while the smooth slopes the world. Navajo Sandstone cliffs are particularly 50 Chapter 3

3.3. Large-scale tangential cross-bedding reflects the eolian (wind-deposited) origin of the Navajo Sandstone in the San Rafael Swell. Courtesy John Telford. impressive in the Zion National Park region, where sweeping etching on cliffs and bald knobs known as they tower over 1,500 feet, but they are prominent “slickrock” throughout the canyon country of east- features of the landscape wherever the formation is ern Utah (fig. 3.3). These features provide evidence exposed (fig. 3.2). that the vast amounts of sand in the Wingate and The sandstones that dominate the Glen Canyon Navajo Sandstones represent wind-blown parti- Group, in the Wingate and Navajo Formations, are cles that accumulated in immense dune fields. Such mostly composed of sand grains smaller than about large dune fields, like the “sand sea” of the modern 0.02 inch. The sand grains commonly have abraded Sahara Desert of north Africa, are known as ergs. or “frosted” surfaces, an effect of the natural sand- Sandstones that represent wind-transported accu- blasting that accompanied their transport. Outcrops mulations are referred to as eolian deposits. The ergs of these sandstones commonly exhibit spectac- represented by the Wingate and Navajo Sandstones ular large-scale cross-bedding that produces the were of impressive extent, at times approaching The Early and Middle Jurassic 51

3.4. The immense Navajo sand sea covered at least 3.5. The Wingate Sandstone erg was the first of two 160,000 square miles of western North America. Recon- large dune fields to develop in the early Jurassic. Along struction from Ronald Blakey/Colorado Plateau Geosys- the southwest margin of this erg, fluvial and lake sedi- tems, Inc. Used with permission. ments of the Moenave Formation were deposited at the same time as the Wingate Sandstone. Reconstruction from Ronald Blakey/Colorado Plateau Geosystems, Inc. Saharan proportions during the early Jurassic. This Used with permission. is especially true of the Navajo Sandstone, which can be traced northward from southern Utah well the Empty Quarter in modern Saudi Arabia. Dur- into Wyoming, where it is known as the Nug- ing Wingate Sandstone time the erg was somewhat get Sandstone. To the southwest the Navajo erg smaller and only covered the eastern half of Utah extended into the Mojave Desert region of south- plus a small portion of adjacent areas (fig. 3.5). east California, where the eolian sand deposits are The orientation of the cross-beds in such sand referred to as the Aztec Sandstone. deposits can provide information on the direction Thus the Navajo-Nugget-Aztec erg covered much of sand transport. For the Navajo Sandstone the of the southwestern portion of North America just sand grains were derived mainly from the north as modern north Africa is mostly covered by Saha- and northwest, blown into the interior basin from ran sand. The Navajo Sandstone erg covered at least that direction in successive “waves” of sand, some 160,000 square miles, based on the current extent up to 50 feet high (Young 1987). The sand accumu- of the Navajo and correlative formations (fig. 3.4). lated across the floor of the central Utah interior Because the modern distribution of the Navajo-Nug- basin, which was still surrounded by highlands to get-Aztec sand deposits has been reduced by post- the west, south, and east. In western Utah and east- Jurassic erosion, the original erg might have been ern Nevada the Mesocordilleran High, which began twice that size. The early Jurassic sand sea of western to develop in late Triassic time, became even more North America was larger than the modern Sahara prominent in the Jurassic as igneous activity and erg and is comparable to the spacious dune fields of compressional forces became active in the region 52 Chapter 3

(Miller and others 1987; Hintze 1988; Miller and the surface by blowing away the dry sand and silt is Hoisch 1995). To the south the ergs were limited by known as deflation. chains of volcanic mountains in south-central Ari- Deflation basins between the crests of advancing zona, from which a broad slope descended to the dunes can temporarily capture rainwater or allow north into Utah’s interior basin (Riggs and Blakey groundwater to seep to the surface to form a moist 1993). East and southeast of the sand seas, in Col- substrate. The momentary abundance of water in orado and southeast of the Four Corners region, these deflation basins may allow plants to germi- low hills and benches served as barriers to the dune nate, giving rise to a small pocket of lush vegetation fields. To the north, beyond the open end of the in the midst of a biological wasteland. The deflation interior basin, the great sand sheets extended to the basins, ephemeral lakes, and oases of sandy deserts shoreline of the early Jurassic seas, located in what act like biotic magnets, attracting great numbers is now Wyoming, Montana, and Idaho. The sandy of animals to drink, feed on whatever plants might beaches of this coastline must have been the source be growing at the water’s edge, or lie in wait for for much of the sand deposited in the early Juras- prey to approach. In the early Jurassic sandstones sic ergs. The eolian deposits that dominate the Glen of Utah such interdune deposits are represented by Canyon Group signify the burial of the old Chinle thin and laterally discontinuous lenses of mudstone basin under sheets and dunes of wind-driven sand and limestone that are interbedded with the much derived from the north and northwest. The move- thicker and more extensive eolian sandstones. The ment of such massive amounts of sand requires a deflation surfaces appear as prominent horizontal dry and windy climate. The relative verdant, well- planes, known as “first-order bounding surfaces,” watered basin of the late Triassic became a searing among the complex pattern of sweeping cross-beds desert in the early Jurassic. In the context of such that typifies eolian sandstones. Many deflation sur- an acute shift in the regional environment, the Tri- faces and lenses of interdune deposits occur in the assic-Jurassic biotic transition certainly comes as massive Navajo Sandstone, and some are known no surprise. from the Wingate. Both fossils and footprints prin- Though the Glen Canyon Group is dominated cipally occur in these zones in these two eolian for- by eolian sandstone, which documents an enor- mations (Winkler and others 1991). In addition, the mous and persistent desert, it also contains other early Jurassic ergs were laced by dry washes that types of deposits that are extremely important as channeled runoff into the temporary lake basins sources of information on the animals that inhab- after the rare cloudbursts. Sand would periodically ited the erg and nearby regions. All large ergs have drift into the washes, only to be scoured away dur- interdune areas where the infrequent rainfall may ing a subsequent desert flash flood. Some of the become ponded in ephemeral or playa lakes. Such sandstone layers in the Navajo and Wingate rep- lakes are short-lived, usually disappearing in a mat- resent reworked eolian sand spread out across the ter of days in the blistering climate of the desert. floor of the dry washes during flood events. In addition, groundwater occasionally rises to the In the case of the Wingate Sandstone the rela- surface in places like the modern Sahara to form tively small erg covered only the eastern half of Utah spring-fed oases that represent the only semiperma- (fig. 3.5). On its southwest margin a complex river nent bodies of water in the otherwise barren sandy system separated the erg from the foothills of the landscape. As large dunes migrate downwind, the Mesocordilleran High to the west. This river system dry sand is blown over and past the more cohesive transported water and sediment to the northwest, and moist sediment below so that the land surface is toward the sandy beach beyond the open end of the lowered as the dunes pass. The process of lowering interior basin. The wind would then blow the sand The Early and Middle Jurassic 53 back into the erg. Some of the sand and silt carried broad surface of sediment transported by a braided by the river system was deposited along its course stream system is known as a braid plain. The Kay- and over the adjacent floodplain. These river-depos- enta Formation represents a braid plain interlude ited sediments flanking the eolian sandstones of the between two episodes of erg development. The cli- Wingate compose the major portion of the Moenave mate in Kayenta time was probably still desertlike, Formation. The Moenave is restricted to southwest but dune fields were only a restricted element of the Utah and northwest Arizona and is equivalent to at scene during that brief phase of a river-dominated least the upper part of the Wingate Sandstone, into arid landscape. In the northeast corner of Utah, which the fluvial sediments pass as they are traced around Dinosaur National Monument, the Glen east. The Moenave fluvial system drained the slope Canyon Group consists of about 700 feet of eolian descending from the volcanic highlands of south- sandstone without the fluvial Kayenta component. central Arizona and carried water around the Wing- Evidently the braid plain constructed by the Kay- ate erg. The river-plain habitat, with more plentiful enta Fluvial system did not extend into this corner water, probably supported a richer biota than the of Utah: the dune fields persisted there throughout sand sea to the northeast during Wingate-Moenave the entire early Jurassic. time. In the area around St. George the sediments preserved in the Moenave Formation document Paleontology of the Glen Canyon Group: the presence of a large freshwater lake named Lake A New Array of Dinosaurs Dixie by scientists (Kirkland and Milner 2006). The sediments deposited in and around this lake pre- Until very recently our knowledge of the life that serve a spectacular array of footprints, trackways, existed in and around the great ergs and braid plains and fossils that provide important clues to the dino- of the early Jurassic was extremely limited due to saur fauna that inhabited early Jurassic Utah. the rarity of fossils from rocks of this age. This scar- As noted, the development of ergs in the early city of body fossils resulted from at least three fac- Jurassic occurred in two phases: the relatively small tors. First and foremost, deserts are generally Wingate erg and the much larger and later Navajo regions of minimal biological productivity. The lack erg (fig. 3.4). Between these two episodes of sandy of water in the early Jurassic would have restricted deserts, a large river system similar to the Moenave the growth of plants, which in turn meant lim- fluvial complex evidently covered this entire portion ited food resources for herbivores and few prey ani- of eastern Utah. Thus the Kayenta Formation, which mals for carnivores. Modern deserts are infamous separates the Navajo and Wingate Sandstones, con- for their stark and lifeless visage, a consequence of sists almost entirely of river deposited sand, silt, and the minimal presence of life in such hostile envi- mud. For some reason the amount of sand blowing ronments. The desert landscapes of the early Juras- into the interior basin diminished during Kayenta sic throughout the Colorado Plateau region were time. The rivers draining to the northwest began certainly more barren than in the preceding late to penetrate into the older Wingate erg, picking up Triassic (Chinle time). Second, the constant shift- great amounts of loose sand. The rivers developed ing of sand as large dunes migrated across the erg braided patterns as huge sandbars choked the chan- would have resulted in the alternate burial and reex- nels and forced the streams to fork and split as the posure of the organic remains. Such events do not water they carried passed around the sandy obstruc- favor preservation of fossils. Finally, the cliff-form- tions. As the braided pattern developed, a broad ing nature of the eolian sandstones that domi- plain laced by numerous criss-crossing watercourses nate in the Glen Canyon Group makes it difficult evolved on top of the buried Wingate erg. Such a for scientists to find the few fossils that might be 54 Chapter 3 preserved in these rocks. The vertical walls of rock other studies). The discovery of the extensive track- are for the most part impossible to survey for fos- bearing horizons in the Moenave Formation near St. sils in any detailed or comprehensive manner. Most George in 2000 stimulated a unprecedented surge of the fossils that have been found in these forma- of interest among paleontologists (see summary in tions were located either in blocks that have fallen Milner and others 2006b). from the cliffs or in the few areas where the strata are exposed along the level ground surface. The St. George Dinosaur Discover Site: We do have some fossils and recent discoveries, A Glimpse into the Early Jurassic Dinosaur Fauna however, such as the spectacularly abundant footprints at the St. George Dinosaur Discovery Site Though early Jurassic dinosaur footprints from (SGDS). These are beginning to reveal some inter- southwest Utah had been known for decades, the esting details about a heretofore poorly documented discovery of extensive track-bearing surfaces in the fauna that thrived among the dunes and along the Moenave Formation by Sheldon Johnson in 2000 watercourses of early Jurassic Utah. Moreover, the has provided a wealth of new information on the dinosaurs and other terrestrial vertebrates known dinosaurs and environments that existed in the from these rocks indicate a much different commu- region approximately 195–198 million years ago. nity from that of the underlying Chinle Formation. The principal track-bearing horizon is now par- The Triassic-Jurassic transition is clearly evident tially exposed and preserved for public viewing at when we compare to the two fossil assemblages. the St. George Dinosaur Discovery Site at Johnson Farm (SGDS). Since the initial discovery and development, more than twenty recent scientific studies Dinosaur Footprints from the Glen Canyon Group have focused on the sediments (e.g., Kirkland and The footprints of dinosaurs and other vertebrates Milner 2006), footprints and trackways (e.g., Milner are fairly common in many horizons in the Wingate, and others 2006b; Milner and others 2009), and fos- Moenave, Kayenta, and Navajo Formations. Foot- sils (e.g., Milner and Kirkland 2006) of the Moenave prints tend to be more common in the finer-grained Formation at the SGDS. Collectively these studies mud and silt deposited by rivers that ran through have provided a wealth of new information that illu- or beside the erg and in the silty limestone and mud minates a critical and heretofore somewhat obscure that accumulated in oasislike interdune ponds. The chapter in the story of Utah dinosaurs. water at such sites would have attracted great num- Well-preserved footprints and trackways are bers of animals, and the soft, tacky mud at the found in twenty-five different layers within the water’s edge would have served as a good medium Whitmore Point Member of the Moenave Forma- for the preservation of footprints and trackways, tion at the SGDS (fig. 3.6). The Moenave Formation recording the comings and goings of life drawn in in this area consists of sandstone, mudstone, and from the surrounding desert. Some footprints have shale deposited along the edge of Lake Dixie (Mil- been discovered in the dune sands as well; many of ner and Kirkland 2006, 2007). This shallow saline them appear to have been made when the sand was lake was subject to significant fluctuation in size and moistened by dew or rain and therefore more cohe- depth over time. At its maximum size Lake Dixie sive than it normally was. Many studies of dinosaur completely submerged the area from St. George to footprints from early Jurassic strata of Utah have Kanab and extended north beyond the present site been completed over the past two decades (e.g., of Zion National Park. Smaller fluctuations of lake Stokes 1978; Stokes and Madsen 1979; Baird 1980; level may have occurred on a seasonal basis, result- Lockley 1991b; Lockley and Hunt 1995, among many ing in the frequent shifting of the shoreline of Lake 3.6. Distribution of track-bearing horizons and body fossils in the Moenave Formation at the St. George Dinosaur Dis- covery Site (SGDS) in southwest Utah. From Milner and others 2009. 56 Chapter 3

lungfish, coelacanths (lobe-finned fish), and heavily armored relatives of the modern gar known as semi- onotids (fig. 3.7). These fish were relatively large, with some of them attaining maximum lengths approaching 2 meters (6 feet). Agal structures and fossils of conchostracan crustaceans (commonly known as “clam-shrimp”) are also preserved in the Moenave sediments and provide additional evidence of a thriving aquatic ecosystem in Lake Dixie. Fragmentary plant fossils in the lakeshore sediments suggest the presence of trees and shrubs along the shore of Lake Dixie and the streams that drained into it. In addition to the fossils of aquatic animals and plants in the Moenave Formation, more than six thousand well-preserved footprints have been discovered in these strata at or near the SGDS. These clearly indicate that dinosaurs were frequent visitors to the shores of Lake Dixie. The footprints at the SGDS are dominated by relatively small Grallator tracks (about 95 percent of the preserved tracks) and large Eubrontes tracks, both likely made by predatory and bipedal theropod 3.7. Fish from the Moenave Formation at the St. George dinosaurs. The larger Eubrontes tracks are gener- Dinosaur Discovery Site: A. a large coelacanth; B. Cera- ally 30–45 cm (12–18 inches) long and have narrow todus stewarti, a lungfish; C. Semionotus kanadensis, a primitive bony fish; D. Lissodus johnsonorum, a fresh- marks made by sharp claws at the tips of the toes water shark. Scale bar = 1 foot (0.3 m). Based on recon- (fig. 3.8). Based on the size of the Eubrontes tracks, it structions of Milner and Kirkland 2007. appears that a theropod dinosaur much larger than Coelophysis of the late Triassic prowled the shores of Dixie across the low basin in southwest Utah. The Lake Dixie. A good candidate for the track-maker sediments in the Moenave Formation at the SGDS of the SGDS Eubrontes tracks is Dilophosaurus are thus a mixture of fine-grained open-water (described below) from the overlying Kayenta fauna deposits, sandy lakeshore sediments, and material or a theropod similar to it. Supporting this conclu- washed into the lake by ephemeral streams. When sion are a few fragmentary fossils (portions of ver- the level of Lake Dixie fell, extensive mudflats would tebra) and dinosaur teeth in the track-bearing layers have been exposed in the wake of the receding that could have belonged to Dilophosaurus or some water, only to be resubmerged when the lake later very similar animal. The smaller but more abun- expanded. Mud cracks and diamond-shaped salt dant Grallator tracks (fig. 3.9) appear to be made by crystal casts are common in the Moenave Forma- a Megapnosaurus-like theropod, also known from tion at the SGDS and provide evidence for periodic the Kayenta Formation (described in more detail in exposure of fine-grained lake-bottom sediments. a later section). In addition, Batrachopus, a footprint Fish fossils found in the Moenave Formation thought to have been made by a primitive crocodil- at the SGDS indicate that Lake Dixie was popu- ian reptile, also occurs in the Moenave Formation in lated by a variety of primitive fish, including sharks, southwest Utah. The Early and Middle Jurassic 57

3.8. A well-preserved Eubrontes track from the St. George Dinosaur Discovery Site. Total track length is about 14 inches. Photo by Frank DeCourten. 3.10. A dinosaur swim track known as Characichnos from the St. George Dinosaur Discovery Site. Track length is 6 inches. Photo by Frank DeCourten.

theropod dinosaurs slipping and sliding just above the muddy floor of the lake (fig. 3.10), as the animals ventured in the channel and were swept off their feet by the current. The swimming tracks are mostly similar in size to the small Grallator tracks and are generally oriented upstream with respect to the current direction indicated by structures in the sandstone. Paleontologists Andrew Milner and James Kirkland have presented very good evidence suggesting that these tracks may have been made by small to medium-sized theropod dinosaurs hunting 3.9. Grallator tracks like this one, about 3 inches long, are the most common type of footprint at the St. George fish in the shallow water of Lake Dixie (Milner and Dinosaur Discovery Site. Photo by Frank DeCourten. Kirkland 2007). Elsewhere in southwest Utah the Moenave Formation has produced additional ver- A fascinating aspect of the theropod tracks pre- tebrate footprints and trackways in dozens of loca- served at the SGDS is the discovery of swimming tions (Foss and others 2009). tracks associated with a sandstone layer that was deposited in an offshore channel in Lake Dixie (Mil- Other Tracks of the Glen Canyon Group ner and others 2006a; Milner and Kirkland 2007). In southwest Utah the Wingate Sandstone was The swim tracks typically occur as sets of three par- deposited in the great erg east of Lake Dixie while allel and elongated scratch marks on the bottom the sediments of the upper Moenave Formation of the sandstone bed that was deposited in a shal- accumulated along the lakeshore. Thus the Wing- low offshore channel by currents in Lake Dixie. ate Sandstone is in part the lateral equivalent of the The parallel grooves were initially excavated in the Moenave Formation and accumulated at about the fine sediment of the channel bottom and were later same time some 200 million years ago. Not sur- buried under sand that accumulated on the lake prisingly, vertebrate tracks preserved in the Wing- floor. These tracks suggest the claws on the feet of ate Sandstone are dominated by large three-toed 58 Chapter 3 tracks, 6–8 inches (16–20 centimeters) long, gener- footprints from the Wingate, Moenave, and Kayenta ally similar to the Eubrontes type from the Moenave Formations suggest a dinosaur-dominated commu- Formation. These tracks indicate a somewhat larger nity of terrestrial vertebrates living in the ergs, along theropod (perhaps 3 feet [1 meter] or so high at the the lakeshores, and over the braid plains in Utah in hip) than theropods such as Coelophysis known the Early Jurassic. They may have shared these habi- from the underlying Chinle Formation, though tats with crocodilian reptiles and possibly birds. The smaller Grallator types of tracks are also known. footprint record yields little evidence of the other The Kayenta Formation also produces relatively types of the nondinosaur reptiles (rauisuchians, abundant footprints, including the Eubrontes type phytosaurs, and so forth) that were so common in similar to those of the Wingate and Moenave For- the Chinle Formation. Those reptiles apparently had mations. For example, dinosaur footprints in the become victims of the Triassic-Jurassic extinctions. Springdale Member (a subdivision of the Kayenta By early Jurassic time the dinosaurs were beginning Formation) in Warner Valley and other sites near to take over. St. George (Miller, Britt, and Stadtman 1989; Ham- The Navajo Sandstone is the youngest compo- blin and others 2006) indicate the presence of at nent of the Glen Canyon Group and accumulated least three different types of dinosaurs living along in an expansive erg some 180–190 million years ago. the river plain. A large bipedal theropod, a smaller In the Navajo Sandstone are preserved abundant Coelophysis-like carnivore, and possibly a prosau- trackways and footprints that reveal the presence of ropod dinosaur all tramped through the fine sand many new varieties of dinosaurs, other reptiles, and and mud deposited at this site during the early (probably) primitive mammals. Vertebrate tracks Jurassic. As we will soon see, this set of footprints are known from the Navajo Sandstone at numerous is perfectly compatible with the types of dinosaurs localities in Utah and range from tiny, birdlike foot- known from Glen Canyon strata in other locations. prints barely an inch long to much larger tridactyl Thus we know that at least several different types (three-toed) prints over 1 foot (0.3 meter) in length. of dinosaurs were prowling the edge of the Wing- These forms are generally similar to the Gralla- ate erg. tor-Eubrontes family of footprints and were prob- Also known from the Kayenta are some very ably made by small and large theropod dinosaurs, interesting three-toed tracks that sometimes have respectively, or perhaps even by birds (for the small- smaller four-digit impressions associated with them. est tracks). In addition to these footprints, the track These tracks, known as Anomoepus, suggest a dino- assemblage in the Navajo Sandstone includes many saur that was capable of shifting its stance from other interesting forms. Brasilichnium, for example, bipedal to quadrupedal while it walked, with the is a small, oval track about 1–3 inches (3–8 cm) wide smaller four-digit track representing the forefoot with four or five stubby toe impressions (fig. 3.11D). or “hand” impression. Finally, the Kayenta Forma- Brasilichnium tracks look much like the footprint of tion has also produced some very small (a little less a tiny dog and have at least two characteristics sug- than 1 inch [2.5 cm] long), three-toed tracks that gesting mammal origin: wide feet (broader than have very slender toe impressions. These tracks may they are long) and short toes (Lockley and Hunt have been made by baby theropods or perhaps rep- 1995). Some very “mammal-like” reptiles, known resent footprints left by early birds. Recall that the as tritylodonts (more about them later), are known first bird probably originated from its dinosaur- from the fossils of the Glen Canyon Group. Most like ancestor sometime prior to the late Jurassic. The paleontologists think that Brasilichnium represents “bird”-like tracks of the Kayenta might actually rep- tracks made by tritylodonts or other animals similar resent the earliest evidence of avian creatures. The to them. Lizard tracks, given the name Lacertipus, The Early and Middle Jurassic 59

3.11. Early Jurassic tracks of the Glen Canyon Group of eastern and southern Utah: A. small Grallator tracks from the Moenave Formation; B. much larger Eubrontes tracks from the Moenave Formation (compare with figure 3.8); C. Navahopus tracks from the Navajo Sandstone, a possible prosauropod trackway; D. Brasilichnium from the Navajo Sandstone; E. Oto- zoum, possible prosauropod from the Navajo Sandstone near Moab. Bar in all sketches = 4 inches (10 cm). A and B: from Miller and others 1989; C–E: from Lockley and Hunt 1995.

are often associated with mammal-like tracks in the with a long first digit. The best candidates for the Navajo Sandstone. originators of Otozoum and Navahopus from the With respect to dinosaurs, perhaps the most sig- Navajo Sandstone are the prosauropods, which have nificant tracks in the Navajo Sandstone are the large all the characteristics suggested by the tracks. Skel- four-toed tracks known as Otozoum and similar but etal remains of prosauropods are known from the smaller footprints referred to as Navahopus. Oto- Navajo Sandstone, so it is reasonable to associate zoum tracks are a foot or more in length and about 8 Otozoum and Navahopus with two different kinds inches (20 centimeters) wide (fig. 3.11E). Trackways or sizes of prosauropods walking among the dunes with several Otozoum prints aligned in sequence of the Navajo erg. Overall the abundant and varied have no smaller forefoot impressions, suggesting dinosaur track assemblage preserved in the Navajo that the track-maker was a large biped. In Navaho- Sandstone suggests that the trend toward greater pus, the smaller (5–6-inch-long [about 14-centime- dinosaur size, dominance, and diversity continued ter]) four-toed hind footprints are associated with throughout the time represented by the Glen Can- 2-inch-wide (5-centimeter) forefoot prints, implying yon Group. a quadrupedal track-maker with larger hind limbs than forefeet (fig. 3.11C). The front foot impres- Dinosaur and Other Body Fossils sions in Navahopus bear a pronounced claw mark from the Glen Canyon Group directed inward, suggesting a robust “thumb” on the front feet of the creator of the print. Thus these two Until the early 1980s we knew very little about the types of tracks could have been made by a group of animals that inhabited the early Jurassic ergs of large dinosaurs that had four well-developed toes on Utah and adjacent regions from fossils represent- their hind feet, were capable of both quadrupedal ing skeletal remains. Some sporadic reports of ver- and bipedal posture, and had forefeet (or “hands”) tebrate fossils came from the region as early as the 60 Chapter 3

1930s (e.g., Brown 1933; Camp 1936), and a few more have weathered out of the Chinle sediments prior to discoveries had been made by the late 1950s (Welles deposition of the Wingate sands. The fossils appear 1954; Lewis 1958). In the late 1970s and early 1980s to be uneroded, however, so they might represent intensive collecting from the Kayenta Formation of the remains of phytosaurs that somehow managed northern Arizona by the Museum of Northern Ari- to live in Utah as the dunes advanced inland. Per- zona, the Museum of Comparative Zoology at Har- haps the conditions in the Wingate erg were not as vard University, and the University of California extremely dry and hostile as we have assumed. The Museum of Paleontology produced abundant fos- interdune oases may have been more persistent fea- sil material and stimulated great interest in the fos- tures than they are in today’s Sahara erg, allow- sil fauna of the Glen Canyon Group. In addition, ing populations of semiaquatic reptiles to become new fossils from the Navajo Sandstone were later established in that otherwise harsh environment. discovered (Sertich and Loewen 2010; Irmis 2005) However they may have come to reside where they that documented the first appearance of several new were found, these remains probably represent the types of dinosaurs in the Utah region in the early last of the phytosaurs; no trace of them is found in Jurassic. As a result we can now recognize a distinc- rock layers younger than the Wingate Sandstone. tive early Jurassic dinosaur fauna accompanied by a Recall that the Moenave Formation represents variety of nondinosaurian vertebrates from the Col- sediment deposited in a river and lake system that orado Plateau region. Knowledge of this fauna is skirted the Wingate erg on the southwest. The Moe- still incomplete, however, and many of the fossils nave river plain must have been a much more fertile on which it is based are known only from Arizona. realm than the scorched and gusty Wingate des- Because the ergs and erg-margin environments of ert and at times even had enough water to maintain the early Jurassic extended over the entire Colorado ephemeral Lake Dixie. It is not surprising that most Plateau region, it is likely that the Arizona forms of the fossils from the earliest part of the Jurassic also existed in Utah. In any case the recent discov- come from the Moenave, not the Wingate Forma- eries are beginning to hint at a fascinatingly varied tion. Common vertebrate fossils from the Moenave array of dinosaurs that lived in the Utah region by Formation include the remains of the early croco- about 180 million years ago. As scientists continue dile Protosuchus (Brown 1933; Colbert and Mook to search for fossils from the Glen Canyon Group in 1951). This reptile probably lived in the rivers that Utah, it is likely that we will confirm the presence of deposited the Moenave sediments, but it seems to the Arizona forms, and perhaps even discover new have possessed a more erect stance and therefore types, from the southeastern part of the state. was somewhat better adapted for terrestrial locomo- Only one identifiable fossil other than the foot- tion than modern crocodiles. Perhaps the streams prints already described has been found in Utah flowing along the southwest margin of the Wing- exposures of the mostly eolian sandstones of the ate erg were shallow and/or ephemeral. Protosuchus Wingate. M. Morales and S. R. Ash (1993) reported appears to have been well adapted for such a river phytosaur remains in the lowermost part of the system and may have prowled the shores of Lake Wingate Sandstone in the vicinity of Big Indian Dixie as well. Rock, north of Monticello. How the remains of Along with the abundant footprints and track- aquatic creatures like phytosaurs came to be pre- ways, some scrappy remains of dinosaurs are also served in these eolian sandstones is an interesting preserved in the Moenave Formation of south- mystery. The fossil phytosaur material came from ern Utah. Several isolated teeth belonging to car- the lower Wingate Sandstone, just above its contact nivorous dinosaurs have been discovered at the St. with the underlying Chinle beds, so the bones may George Dinosaur Discovery Site, some exceeding The Early and Middle Jurassic 61

3 inches (7.5 centimeters) in length. Though they most paleontologists place them into that class with- are rare, these tall, slender teeth, coupled with the out question. sharp serrated edges on the front and back, clearly What were the tritylodonts and other herbivores indicate a dinosaur predator larger than Coelo- eating? Plant fossils are not abundant in the Kay- physis and its contemporaries. Interestingly, Mil- enta Formation, but occasional fragments of fossil ner and Kirkland (2007) have noted that several wood suggest that plants existed across the flood- of these teeth show significant wear that might be plains and along the river channels. Genuine forests attributable to repetitive biting through the heavy, may have grown on the higher slopes of the Kayenta thick scales that armored the bodies of some of the watershed. Two different flying pterosaurs also have large Lake Dixie fish. been identified from Kayenta sediments, including Rhamphinion, named on the basis of fragmentary fossils found in northern Arizona (Padian 1984). The Kayenta Fauna Rhampinion was about the size of a large hawk, with The Kayenta Formation, because of its dominantly a wingspan of about 4 feet (1.3 meters). These ptero- fluvial origin, has produced the vast majority of fos- saurs represent the oldest known flying reptiles in sils known from the Glen Canyon Group. Its ver- North America. It is clear from this partial list of tebrate fauna is rich indeed. Protosuchus was still Kayenta fossils that the river system of Kayenta time present in Kayenta time but was joined by several was populated by many different kinds of aquatic, other types of crocodilians, such as Eopneumato- terrestrial, and aerial vertebrates. suchus (Crompton and Smith 1980). Fossils of tur- Dinosaurs are also known from Arizona expo- tles and frogs, both aquatic animals, have also been sures of the Kayenta Formation and almost certainly found in the Kayenta Formation. The advanced lived in Utah as well. Relatively complete and well- herbivorous mammal-like reptiles known as trity- preserved fossils of two different crested theropods lodonts were especially abundant and diverse dur- have been found in these strata. The first Kayenta ing Kayenta time. Kayentatherium (fig. 3.12) is the theropod was discovered in 1942, originally referred most common of this group and may be close to the to as Megalosaurus wetherilli and later renamed ancestor of later Mesozoic mammals. Some early Dilophosaurus wetherilli (Welles 1954; Welles, 1970). members of those advanced mammal groups are Additional specimens of Dilophosaurus recovered also known from the Kayenta Formation. Morga- from Arizona localities in the 1960s have greatly nucodon and Dinnetherium, for example, have both improved our knowledge of this “doubled crested been recovered from Arizona localities and are so far along the evolutionary path to mammals that

3.12. Kayentatherium, an early Jurassic tritylodont mammal from the Kayenta Formation. Skull is about 10 inches long. Adapted from Carroll 1988 (cited in chapter 3.13. Dilophosaurus, a theropod dinosaur from the Kay- 1 references). enta Formation. 62 Chapter 3 reptile” (Welles 1984). This dinosaur was a fearsome beast, with sharp daggerlike teeth lining the jaws of a skull that sported two large crests of bone flaring upward from the head (fig 3.13). It was approximately 18 feet (6 meters) long, weighed in at some 600–700 pounds when full grown, and held its ornate head some 6–7 feet (about 2 meters) off the ground. The function of crests on the skull of Dilophosau- rus is still conjectural, but they certainly contributed 3.14. Skull of Megapnosaurus as it was discovered in to a more threatening countenance. Perhaps the the Kayenta Formation of northern Arizona. The ring crests were used to attract mates or to discourage of small bones in the orbit (eye socket) surrounded the competitors. The bone in the crests is very thin, so it eye. Bar = 2 inches (5 cm). After Rowe 1989. is unlikely that the crests were used in head butting or defense. This theropod was fully bipedal and was Hollywood hype. Besides, with all its other weapons probably speedy, although the legs were not as long such as speed, agility, claws, and dental daggers who as those of more advanced theropods. Because Dilo- needs poison (particularly if at least some of its food phosaurus has several relatively primitive features consisted of creatures that were already dead)? (such as four fingers on its reduced forelimbs), it Megapnosaurus kayentakatae is another cera- belongs to the relatively unadvanced group of thero- tosaurid theropod known from the Kayenta For- pods known as ceratosaurs. Primitive though it may mation of Arizona, as the species name suggests. have been, Dilophosaurus was probably the larg- This theropod, originally named Syntarsus but later est of the dinosaur predators inhabiting the Kayenta renamed to avoid confusion with a beetle bear- landscape. S. P. Welles (1984) noted that the bone ing the same name, was a small theropod, about at the tip of the snout (the premaxilla) was weakly the same size as Coelophysis of the late Triassic and attached to the rest of the skull, suggesting that Dilo- only about half as large as Dilophosaurus. It also had phosaurus could not have generated a very powerful a crest running along the top of its skull, but this bite. This provides some evidence that Dilophosau- appears to have been much less pronounced than rus may have “pecked” at its prey in a manner sim- the double crest of Dilophosaurus. The approxi- ilar to the way a vulture dismembers and consumes mately 9-inch-long (23-centimeter) skull of this the- the carcass of a dead animal. Dilophosaurus was ropod was equipped with dozens of sharp, curved probably not restricted to a scavenging diet, how- teeth, all shorter than about 1 inch (fig. 3.14). Mega- ever, because the sharp claws that tipped three of the pnosaurus, while still considered to be a relatively four fingers on its hand could certainly have func- primitive ceratosaur, is the most advanced member tioned as effective killing weapons. In addition to of that group. Several of the ankle bones of Mega- consuming the remains of animals that had already pnosaurus were fused to form a strong joint, with expired, it is likely that Dilophosaurus occasion- motion restricted to the fore-and-aft plane. The foot ally used its speed to catch smaller and slower ani- is extremely birdlike, suggesting a quick and agile mals, ripping them with the talons of the forelimbs. animal. Megapnosaurus evidently preyed on smaller By the way, we have no solid evidence that Dilopho- and more elusive creatures than Dilophosaurus did, saurus could spit poison, as the down-sized indi- such as lizards and mammal-like reptiles. The two viduals of this species were depicted doing in the known Kayenta theropods or other predators simi- popular movie Jurassic Park—that behavior is sheer lar to them may be the originators of the three-toed The Early and Middle Jurassic 63

3.15. Massospondylus, an early Jurassic prosauropod: A. skull of Massospondylus (bar = 2 inches [5 cm]); B. lateral and occlusal view of a typical tooth, about 0.75 inch long; C. Mas- sospondylus climbing a sand dune leaving tracks very similar to those of Navahopus and Otozoum. A–B: after Attridge and others 1985; C: adapted from Lucas 1994. footprints in the Moenave and Kayenta sediments at primitive group of saurischian dinosaurs probably St. George, Warner Valley, and other sites in Utah. It walked in a quadrupedal fashion most of the time may be more than a coincidence that the most dom- (fig. 3.15C), but they were no doubt capable of rising inant three-toed dinosaur tracks in these two for- up on their hind limbs in a bipedal posture when it mations and theropod body fossils found in the was advantageous to do so. rocks only slightly younger seem to come in two Prosauropods were almost certainly herbivo- distinct size ranges: small (Grallator and Megapno- rous; one famous specimen of Massospondylus was saurus) and large (Eubrontes and Dilophosaurus). even discovered in Africa with a mass of gastroliths In addition to these dinosaur predators, the preserved within the rib cage, suggesting the pres- remains of herbivorous dinosaurs have also been ence of a gizzardlike organ to help grind plant fod- discovered in the Kayenta Formation. The prosau- der. Massospondylus from the Kayenta Formation ropod Massospondylus is known from the Kayenta is almost identical to specimens of this genus from on the basis of a single nearly complete but dis- southern Africa. Interestingly, the southern Africa torted skull (Attridge and others 1985; fig. 3.15A). specimens come from rocks that were also depos- Prosauropods were one of the first groups of dino- ited in a seasonally arid or semiarid environment, saurs to evolve during the great Triassic radiation of much like the conditions under which the Kay- reptiles. By the early Jurassic the prosauropods had enta sediments accumulated in the Colorado Pla- spread across North and South America and into teau. Massospondylus apparently was specialized for Europe, Asia, and Africa. In their general appear- plant-eating in such occasionally dry habitats. Some ance the prosauropods were similar to the great unique features, however, were observed for the first sauropods that would follow them in the later Juras- time in the skull of the Kayenta specimen. The Ari- sic, with a long neck and tail, but they were much zona specimen evidently had dozens of small (0.05 smaller and had a less bulky build. The teeth of pro- inch [about 1 mm] long) conical teeth on its pal- sauropods were simple and flattened (like a spatula) ate. The function of these tiny teeth is uncertain, with numerous bumps or serrations along the edges but palatal teeth have never been observed in any (fig. 3.15B). The forelimbs of prosauropods were other dinosaur. The skull of the Arizona Massospon- smaller than the hind limbs, but not by much. This dylus also has a pronounced “overbite”: three of the 64 Chapter 3 teeth in the front of the upper jaw hung out over the “chin” (fig. 3.15A). With the discovery of Massospondylus in the Kayenta Formation, the existence of prosauropods in the Colorado Plateau during the early Jurassic is firmly established. We may also have discovered the group of creatures that left the larger tracks, such as Otozoum, Tetrapodichnus, Navahopus, and Anomo- epus in the late Triassic and early Jurassic rocks of Utah. Trackways of probable prosauropod origin are also known from the late Triassic Chinle Formation, so this group of dinosaurs was probably present in the Colorado Plateau for millions of years before their oldest remains were first preserved in the sediments of the Kayenta Formation. Massospondylus was not the only herbivorous dinosaur inhabiting the Kayenta river system. Fos- sils of the earliest North American ornithischian dinosaurs also have been discovered in the Kayenta Formation, again from northern Arizona localities. Two different Kayenta herbivorous ornithischians 3.16. Scutellosaurus, an ornithischian dinosaur from the are known, both of relatively primitive character. Kayenta Formation: A. reconstruction of the skeleton Scutellosaurus (fig. 3.16) is the better known of the (note the extremely long tail and the rows of scutes cov- two, represented by at least one nearly complete ering the body); B. typical scutes from Scutellosaurus, the largest about 0.75 inch long; C. fragment of the den- skeleton and additional fragmentary fossils (Colbert tary bone from the lower jaw with several teeth (total 1981). Scutellosaurus is one of the earliest and most length approximately 2.3 inches); D. left foot (dorsal primitive members of the Thyreophora, a clade of view: total length about 4.2 inches). All figures from Col- armored dinosaurs that includes the ankylosaurs bert 1981. and stegosaurs that evolved later in the Mesozoic. Scutellosaurus is considered to be a primitive thy- exaggerated tail would have made it difficult for Scu- reophoran because (among other features) the teeth tellosaurus to move in a bipedal fashion, unless the are relatively simple and leaf-shaped compared with body from the hips forward was heavier than the the more complex grinding dentition that would light and delicate bones seem to suggest. It appears later evolve in this lineage. In addition, the pubis is that this was precisely the case: Scutellosaurus, as parallel to the ischium in Scutellosaurus (as it is in the name suggests, was covered by an extensive all ornithischians) but lacks the well-developed for- jacket of bony armor plates (scutes). Several hun- ward extension known as the prepubic process that dred scutes were imbedded in the skin of Scutel- characterizes the more advanced members of its losaurus, forming a knobby shield over most of its clade. body. The armor scutes exhibit a variety of shapes; Scutellosaurus from the Kayenta Formation was those in figure 3.16B exhibit the typical form of not a large dinosaur. It was only about 4 feet (1.3 the scutes covering the back of Scutellosaurus. The meters) in length, about two-thirds of which was weight of all these scutes may have been the rea- accounted for by its very long tail (fig. 3.16A). The son for the unusually long tail: it was necessary to The Early and Middle Jurassic 65

3.17. A scute from Scelidosaurus in lateral (left), dorsal (middle), and ventral (right) views. Note the concave underside of the scute, a feature unique to this ornithischian dinosaur. Scale bar = 0.3 inch (1 cm). After Padian 1989.

counterbalance the heavily armored trunk of this Formation to the Jurassic period was delayed until small dinosaur. Though the well-developed armor recent years because it was thought to contain the of Scutellosaurus suggests a relationship to the later, scutes of late Triassic reptiles. K. Padian (1989) more highly evolved thyreophorans, there are few determined that these scutes belonged to the ornith- other similarities between the skeleton of Scutello- ischian dinosaur Scelidosaurus on the basis of their saurus and those of the ankylosaurs or stegosaurus. unique curved and partially hollowed conical form The teeth of Scutellosaurus were small and leaf- (fig. 3.17). The scutes of aetosaurs are more elon- like, similar to the teeth of most other thyreopho- gated and less conical, with a different pattern of ran dinosaurs (fig. 3.16C). They are clearly the teeth sculpturing. Thus we have no evidence of aetosaurs of an herbivore, designed to shred and strip veg- living on the Kayenta floodplains; the scutes actually etation, but they were probably not very effec- belong to another primitive ornithischian dinosaur. tive in grinding or pulverizing plant material. The Scelidosaurus was one of the first dinosaurs dis- foot of Scutellosaurus has four toes, but only three covered in Europe, where it is represented by nearly of them contacted the ground to support the body complete fossil skeletons. Even though this dino- (fig. 3.16D). The first toe (digit I, equivalent to our saur in known only from isolated scutes in the Kay- “big toe”) was reduced to a stubby prong. With the enta Formation, it appears to have been very similar reduced first toe held above the ground surface, Scu- to the better-known European specimens. Scelido- tellosaurus would presumably have left a small tri- saurus was larger than Scutellosaurus, with a body dactyl hind-foot track similar to those preserved length of about 13 feet or so (about 4 meters). It evi- in the Kayenta Formation at Warner Valley and dently had a more quadrupedal stance than Scutel- elsewhere. losaurus, however, with relatively robust forelimbs Scelidosaurus is another armored ornithischian (fig. 3.18). The teeth of Scelidosaurus were still small known from the Kayenta Formation, but its iden- and simple, much like the teeth of a primitive group tification is more tentative, based solely on isolated of small dinosaurs known as fabrosaurs. Scelido- scutes (Padian 1989). Isolated scutes are not uncom- saurus was probably less mobile and agile than the mon in the Kayenta Formation. After all, these thick smaller Scutellosaurus and likely spent most of its and solid plates of bone are among the most dura- life slowly browsing through the undergrowth of the ble portions of a dinosaur skeleton. For many years sparse forests of the early Jurassic. the isolated scutes of the Kayenta Formation were It is interesting to note that the earliest ornith- thought to have been the remains of aetosaurs, the ischian dinosaurs documented by body fossils in armored herbivorous semiaquatic reptiles of the the Colorado Plateau region, Scutellosaurus and late Triassic. In fact the assignment of the Kayenta Scelidosaurus, were both well armored. The scutes 66 Chapter 3

3.18. Skeleton of Scelido- saurus, about 13 feet long. Modified from Czerkas and Czerkas 1991. imbedded in the skin of both of these dinosaurs barrenness of the modern Saudi Arabian deserts. probably helped them resist the attacks of predators. Such an austere setting would have sustained min- Scutellosaurus in particular, because of its small size, imal biological productivity, compared to the rela- might have been the target of constant assaults from tively fecund habitats of Kayenta time. It is therefore Dilophosaurus, Megapnosaurus, and other (croco- no surprise to learn that, like the Wingate Sand- dilian?) predators. The large size of Scelidosaurus stone, the Navajo Sandstone contains few fossils. It might have deterred some of the smaller carnivores, does furnish some intriguing clues about the nature but additional protection would have been handy of the terrestrial fauna in Utah around 190 million when it confronted the ferocious dilophosaurs. years ago, however, as the early portion of the Juras- Many dramatic struggles between dinosaur predator sic period drew to a close. and prey must have taken place along the Kayenta Footprints of terrestrial vertebrates are not riverbanks and floodplains. uncommon in the Navajo Sandstone in Utah, Ari- zona, Colorado, and Wyoming. As we have already seen, the footprints are most often preserved in Fossils from the Navajo Sandstone: the thin, lenticular sequences of playa or oasis sed- Life in the Sand Sea iments that were deposited between the massive After the deposition of the last fluvial sediments in sand dunes. The track assemblage or “ichnofauna” the Kayenta Formation, sand once again crept into of the Navajo Sandstone is a diverse set of mark- the low basin of eastern Utah from the north and ings probably left by a variety of animals moving northwest. Eventually wind-blown sand accumu- through the great erg. This ichnofauna has also been lated to build a complex of dunes and interdune highly controversial, sparking considerable debate areas similar to the erg of Wingate time but of much on the identity of the track-makers. Various scien- greater magnitude. The Navajo Sandstone, along tists have attributed the Navajo footprints to the with its equivalent units (the Nugget Sandstone to activity of early mammals, prosauropod dinosaurs, the north and the Aztec Sandstone to the south- theropod dinosaurs, crocodiles, and lizards (see west), represents this second early Jurassic sand sea. Lockley and Hunt 1995 for a good summary). The Navajo erg dwarfed the earlier Wingate des- Perhaps the most disputed footprints in the ert, extending from at least southeast California well Navajo Sandstone are those originally ascribed into Wyoming and covering nearly all of Utah (fig. to pterosaurs (Stokes and Madsen 1979) named 3.4). The climate must have become more arid after Pteraichnus (fig. 3.19). The Pteraichnus tracks from the Kayenta fluvial interlude, allowing the reestab- the Navajo Formation were first found around lishment of a sandy desert environment. The deso- Moab, but very similar tracks had been noted earlier lation of the Navajo sand sea must have rivaled the from the late Jurassic Morrison Formation (Stokes The Early and Middle Jurassic 67

unreasonable. The Navajo tracks were found in association with eolian sandstones deposited along the edge of a body of water. The footprints were evidently impressed in the moistened sand at the edge of the water. Isolated pieces of fossil wood are sometimes found in the Navajo Sandstone, creating an interesting image of what parts of the great erg might have looked like. Between the crests of gigantic sand dunes, hundreds of feet high, water would probably collect in many low basins, at least temporarily. The moisture would support the growth of large (tree-sized?) plants. The water would attract dinosaurs and other animals to the pond, while the pterosaurs might have perched on the limbs above, waiting for smaller prey such as lizards and mammals to emerge from the surrounding sand sea. On occasion animals would perish close to the water’s edge. The pterosaurs undoubtedly would swoop down to scavenge at least a portion of the carcass as food. Such bodies of water in the Navajo erg were not permanent or widespread, but they would have 3.19. Pteraichnus tracks from the Navajo Sandstone been great places to catch a glimpse of the life in the near Moab. These tracks were originally attributed to surrounding dune fields. pterosaurs in 1979 but have been vigorously debated ever since. Scale bar = 2.5 inches (6 cm). Modified from Fossil bone in the Navajo Sandstone is extremely Stokes and Madsen 1979. rare, probably due to the minimal populations of animals in the dunes and the low potential for 1957, cited in chapter 4 references) and have since preservation in such a setting. But a remarkably been discovered elsewhere in the western states in well-preserved partial skeleton of a prosauropod several different rock units of Jurassic age. Some dinosaur was excavated by the scientists with the scientists have reevaluated the Pteraichnus tracks Utah Museum of Natural History in 2005 from the since their discovery and considered them to be the base of the Navajo Sandstone (Sertich and Loewen footprints of crocodiles or other terrestrial reptiles 2010). These remains provide a glimpse of the diver- (Padian and Olsen 1984; Lockley and others 2008) sity of dinosaurs wandering the Navajo dunes. rather than of pterosaurs. Other researchers (e.g., Seitaad ruessi is a prosauropodlike dinosaur docu- Kubo 2008) have suggested that modern crocodiles, mented by nearly complete forelimbs, shoulder gir- or creatures like them, are unlikely to have made the dles, and a portion of the vertebral column (fig. Pteraichnus tracks. The issue remains unsettled, but 3.20). This prosauropod dinosaur was about 3 feet it is still likely that flying reptiles lived in the Navajo (1 meter) tall at the hips and perhaps about 15 feet erg of early Jurassic time. (5 meters) long, though only a portion of its spine The earliest-known North American pterosaur is preserved (fig. 3.21). In comparison to the pro- fossils (Rhamphinion) are found in the Kayenta For- sauropods, Seitaad appears to be more advanced in mation, so the interpretation of the Navajo Pteraich- several respects, leading J. J. W. Sertich and M. A. nus markings as pterosaur tracks is not completely Loewen (2010) to consider it an early member of 68 Chapter 3 the sauropod clade that would become the dominant dinosaur herbivores worldwide in the later Jurassic. Weighing less than about 150 pounds when alive, Seitaad was not a large dinosaur but was probably one of the largest herbivores in the Navajo erg. The presence of such an herbivore in the Navajo erg strongly suggests that at least semipermanent stands of vegetation were growing amid the expansive sand sea of the early Jurassic. Like the contemporary prosauropods, Seitaad was probably a habitual quadruped but could also engage in a bipedal stance to reach vegetation or to peer over the crests of sand dunes. The discovery of the remains of a relatively 3.20. Partial skeleton of Seitaad ruessi in matrix rock large herbivorous dinosaur such as Seitaad in the with bones of the forelimb and hand (lower left) and the normally barren Navajo Sandstone provides evi- larger hind foot (lower right) visible. Bar = 2.5 inches (6 dence that the great dunes could support at least cm). From Sertich and Loewen 2010. small populations of larger vertebrates. In addition to Seitaad, another prosauropod, while walking on the hind limbs alone. The skulls Ammosaurus (or Anchisaurus, according to some of Ammosaurus and Seitaad are unknown, which paleontologists who believe that these are two makes it difficult to compare either of these prosau- names for the same animal), has been identified in ropods directly to Massospondylus, for which most the Navajo Sandstone of northeast Arizona (Galton of the postcranial skeleton remains a mystery. It 1971). The Ammosaurus remains from the Navajo may be that Massospondylus is an ancestor to Seit- were not complete but did include some well-pre- aad and Ammosaurus or that these genera repre- served bones of the vertebral column, pes (foot), sent different parts of the same long-lived animal or manus (hand), and limbs. Ammosaurus appears to group of animals. Until more complete fossils of all have been a rather small broad-footed quadruped, a the prosauropodlike genera are found, the three are little over 3.5 feet (about 1 meter) long, of the same considered to be separate but related animals. overall design as Massospondylus. The manus (hand) The only other documented occurrence of dino- of Ammosaurus was about 4 inches (10 centime- saur fossils in the Navajo Sandstone is from a site in ters) wide and possessed a large claw that projected Segi (or Tsegi) Canyon in northern Arizona, where inward. The manus had three well-developed dig- a poorly preserved partial skeleton of a small the- its plus two others that were significantly reduced in ropod dinosaur was discovered in the 1930s. This size. The pes (foot) was larger, about 10 inches (25 dinosaur was named Segisaurus after the canyon in cm) long, with four relatively large toes and a tiny which it was found (Brady 1936; Camp 1936). Segis- vestigial fifth digit. The structure of the manus and aurus appears to have been similar to Coelophysis pes of Ammosaurus is typical of the prosauropods in general appearance. It was a small, gracile pred- and similar to though smaller than the limbs of Seit- ator about the size of a goose and almost certainly aad. Any of the three relatively large early Jurassic belongs with Coelophysis, Megapnosaurus, and Dilo- herbivores (Massospondylus, Seitaad, or Ammosau- phosaurus in the relatively unspecialized cerato- rus) could have made tracks like Navahopus (fig. saurian subdivision of the Theropoda. While the 3.11C) when walking quadrupedally and would have recovered skeleton of Segisaurus is too poorly pre- left footprints similar to Otozoum or Anomoepus served and incomplete to say much more about it The Early and Middle Jurassic 69

3.21. Skeletal reconstruction of Seitaad ruessi from the Navajo Sandstone of southeast Utah. Known elements shown in white; missing portions of the skeleton in gray. Bar = 3 feet (1 m). From Sertich and Loewen 2010. with certainty, it clearly demonstrates that small carnivores accompanied the larger theropods in the early Jurassic of the Colorado Plateau. In summary, the dinosaur fauna of the Navajo Formation includes prosauropods and theropods that appear to be more or less similar to those present in the older Kayenta Formation. In addition, the remains of tritylodont mammals that are nearly identical to Kayentatherium have recently been discovered in the Navajo Sandstone (Winkler and others 1991). From this we can conclude that by about 185 million years ago, during the time of the great Navajo erg and Kayenta braid plain, southern Utah was populated by a diverse dinosaur fauna that was quite different from the array that populated the more luxuriant landscapes of the late Triassic.

Middle Jurassic Marine Invasion 3.22. In middle Jurassic time, a marine transgression in Although eolian sandstone continued to accumu- central Utah from the north submerged most of the great late in spots in eastern Utah after the early Juras- Navajo erg. Reconstruction from Ronald Blakey/Colo- sic, the Navajo Sandstone marks the last time that rado Plateau Geosystems, Inc. Used with permission. a truly immense erg existed in the Colorado Pla- teau region. About 180 million years ago, during the penetrating into the state from the north (fig. 3.22). middle Jurassic, the scene began to change again: Broad areas of Idaho, Montana, and Wyoming the community of terrestrial vertebrates that inhab- were submerged as the marine waters crept over ited eastern Utah was confronted with another pro- the Nugget-Navajo dune fields. As the sea trans- found environmental transformation. Seas returned gressed to the south, it eventually covered much of to east-central Utah during the middle Jurassic, central Utah, submerging the sandy habitat of the 70 Chapter 3 prosauropods and ceratosaurs. At its maximum extent the middle Jurassic seaway of Utah reached as far south as the Zion National Park area. The middle Jurassic seaway of central Utah was a relatively narrow arm of the ocean that was bounded on the west by the Mesocordilleran High and to the east and south by the highlands that circled the older erg basin. Elsewhere in western North America, in areas of lesser relief, the middle Jurassic transgression flooded enormous tracts of low-lying land. With respect to dinosaurs, the main effect of this marine incursion was a drastic reduction of the habitat available to terrestrial animals. Dinosaurs persisted in Utah in the middle Jurassic, but they were restricted to the low coastal plains that surrounded 3.23. The San Rafael Group of east-central Utah. These the middle Jurassic seaway. Consequently the fos- middle Jurassic formations grade into marine deposits sil record of middle Jurassic dinosaurs in Utah and to the west. Thicknesses are approximate and vary from other western states is extremely sparse. The middle place to place. Jurassic, about 185–160 million years ago, remains one of the most mysterious chapters in the story of beds of gypsum, and occasional thin limestone lay- North American dinosaurs. But we do have enough ers. These sediments, a mosaic of marine and terres- clues from rocks formed during this “missing link” trial deposits, accumulated near the eastern margin interval to know that the dinosaurs still populated of the narrow middle Jurassic seaway. To the west the habitats of east-central Utah and to recognize a strata correlative with the San Rafael Group, such as few of the basic types. the Arapien Shale and Twin Creek Limestone, are entirely marine in character. East of the San Rafael Swell region, in the Canyonlands and Moab area, Rocks of the San Rafael Group the San Rafael group is composed mostly of nonma- Above the Navajo Sandstone in most areas of east- rine sediments deposited in coastal dune complexes, ern and southern Utah are several formations con- river floodplains, lagoons, and other marginal sisting of sediment deposited either in the middle marine environments. Jurassic seaway or around its edges. Collectively The seaway that extended south into Utah during this set of formations is known as the San Rafael the middle Jurassic time evidently did not penetrate Group, named for the San Rafael Swell region of very far into western Utah (fig. 3.22). In this area the Emery County where it is well exposed (Thomp- Mesocordilleran High had developed into a con- son and Stokes 1970; Peterson 1988). In this region spicuous mountain terrain as a result of numerous the San Rafael Group (in ascending order) consists bodies of magma rising toward the earth’s surface, of the Page Sandstone, Carmel Formation, Entrada represented today by the intrusive igneous rocks of Formation, Curtis Formation, and Summerville the House Range of Millard County, the Deep Creek Formation (fig. 3.23). This group of formations is Range of western Tooele County, and the Snake dominated by red and brown mudstones and silt- Range in eastern Nevada. These granitic rocks all stones, alternating with lighter-colored sandstones, yield radiometric dates clustering in the middle to The Early and Middle Jurassic 71

3.24. Sandstone of the Entrada Formation near Hanksville. Courtesy John Telford. late Jurassic. It is likely that the intensified igneous that was underway along the southern margin of activity in the middle Jurassic in this region pro- the Colorado Plateau seems to have flared up sig- duced numerous volcanic eruptions, but the rocks nificantly around 170 million years ago, as the sedi- formed during such events have long since been ments of the Carmel Formation were being washed removed by erosion. To the south the presumed vol- into southern Utah (Blakey and Parnell 1995). To the canic arc of south-central Arizona still served as east, in Colorado, the land surface rose gently in a a topographic barrier, although the middle Juras- series of undulating hills of low stature. The eastern sic seaway never came very close to these peaks. boundary of the interior basin was not as sharply The Carmel Formation near Kanab, however, con- defined as were the western or southern margins. tains large boulders of volcanic rocks carried more By the beginning of middle Jurassic time the than 180 miles, probably during catastrophic floods, continued rifting and northward movement of the from sources to the southwest (Chapman 1993). The North American fragment of Pangaea had carried south-central Arizona volcanic chain is the proba- Utah to a latitude of about 25 degrees north of the ble source of these boulders. The volcanic activity equator. The climate was still warm and relatively 72 Chapter 3 dry. Evaporation rates were very high; from time to coastal plain, but no body fossils of such creatures time so much water was removed from the narrow have yet been discovered. sea that layers of salt and gypsum (evaporite depos- Footprints from various horizons in the San its) formed in and around the submerged basin. Rafael Group tell a much different story. The ich- These evaporite deposits are especially prominent nofauna from these strata is rich and profuse and in the Arapien Shale and the Carmel Formation. A affirms the activity of great numbers of terres- broad and low coastal plain developed on the east- trial animals on the eastern margin of the seaway. ern side of the seaway, on which a variety of sed- Particularly impressive is the “megatracksite” at iments were deposited. Coastal dunes formed in the boundary between the Entrada and Summer- places as wind-driven sand and silt were piled along ville Formations in the Moab and Arches National the edge of the seaway. Such middle Jurassic eolian Park area (Lockley and Hunt 1995; Lockley 1991a, deposits are found in the Slickrock Member of the 1991b). This locality, known as the Moab mega- Entrada Formation around Moab (fig. 3.24). Else- tracksite, contains literally millions (perhaps bil- where on the eastern margin of the seaway broad lions!) of tracks and covers an area exceeding 120 mudflats and coastal plains were buried by lay- square miles (fig. 3.25). The track-bearing horizon, ers of fine-grained silt and mud deposited by slug- the surface separating the Entrada Formation from gish rivers draining the low country to the east. The the overlying Summerville Formation, was heavily Summerville Formation consists mostly of such sed- trampled by thousands of dinosaurs traveling along iments, and parts of the Entrada Formation (Dewey the early Jurassic coastal plain in eastern Utah. The Bridge and “earthy” facies) contain similar materi- extreme numbers of tracks preserved at the Moab als. The Curtis Formation consists of pale greenish megatracksite might be a little misleading, how- sandstone representing offshore sandbars produced ever. In part it reflects the minor unconformity (a by tidal surges in seaway. The tidal currents piled gap in time) between the two formations in this part sediment up in great submerged hummocks and of Utah. After the deposition of the uppermost lay- constantly reworked the sandy material across the ers of sediment in the Entrada Formation, there evi- shallow ocean floor. Most of our information on dently was a break in the deposition of sediment for dinosaurs is found in sediments originally depos- an unknown interval of time. The uppermost lay- ited on the muddy and sandy eastern margin of the ers of the Entrada Formation were exposed during middle Jurassic seaway. this hiatus, and groups of dinosaurs moving along the coastal plain could have left many tracks over a long period. Eventually the sediments of the lower Fossils and Footprints of the Middle Jurassic Summerville Formation were deposited across the Only one significant occurrence of vertebrate fos- top of the trampled surface, probably as the result of sils is known from the San Rafael Group of cen- a slight rise in the level of the middle Jurassic sea- tral Utah. The remains of a small (about 9 inches [23 way. Thus the millions of tracks in the Moab meg- centimeters] long) and primitive crocodile known atracksite may signify not just the abundance of as Entradasuchus have been discovered in the Moab dinosaurs but also a lengthy interval of exposure of Member of the Entrada Formation (Hunt and Lock- the upper Entrada beds to track-making activities. ley 1995). In view of the mostly muddy and swampy The individual tracks in the Moab megatracksite are conditions that prevailed on the east side of the made mostly by large three-toed dinosaurs, with middle Jurassic seaway, it is not surprising that croc- feet 12–18 inches (30–45 centimeters) long. Many of odile fossils occur in these rocks. Other vertebrates these tridactyl tracks have sharp claw impressions, must have accompanied Entradasuchus on the low but others do not. This suggests that both theropod The Early and Middle Jurassic 73

3.25. Dinosaur tracks in the Entrada Formation near Moab. Photo by Frank DeCourten. and ornithopod dinosaurs were responsible for the Within the main body of the Summerville For- tracks. mation other very interesting tracks have been Other formations belonging to the San Rafael found that shed additional light on the nature of the Group have also produced tridactyl dinosaur tracks, terrestrial vertebrate community of middle Juras- though not in the stunning abundance seen at the sic Utah. Pteraichnus tracks (arguably made by Moab megatracksite. Near Redfleet Reservoir north pterosaurs) are known from several localities in of Vernal, for example, the Carmel Formation has the Summerville Formation in Utah and its north- produced dozens of three-toed tracks made by small ern equivalent in Wyoming, the Sundance For- theropod dinosaurs (Lockley and Hunt 1995). The mation (fig. 3.26). Unlike the Pteraichnus tracks Carmel tracks are also tridactyl but relatively small, from the Navajo Sandstone, the Summerville-Sun- about 3 inches (7.5 centimeters) or less in length. dance tracks are better preserved, more complete, Some of the Carmel footprints have very slender and more accurately conform to what is known toe impressions and might be attributable to birds. about pterosaur feet, hands, and locomotion (Lock- Quadrupedal dinosaurs do not appear to have been ley and Hunt 1995). Pterosaur tracks have also very common along the eastern shore of the middle been reported from the Curtis and Stump Forma- Jurassic seaway. The plentiful dinosaur tracks tions of the Flaming Gorge Reservoir area (Hayden observed at numerous localities in the Entrada and 2002; Bilbey and others 2005), along with large Carmel Formations provide incontrovertible evi- oval impressions that appear to have been made by dence that great numbers of dinosaurs did populate sauropod dinosaurs. Although none of their fos- the eastern margin of the middle Jurassic seaway, sil bones have yet been found in the Summer- despite the rarity of their fossil bones. ville or coeval formations, we can be confident 74 Chapter 3

3.26. Pteraichnus tracks from the Summerville- Sundance sequence: A. the controversial slab reported by Stokes 1957: when first discovered these loose slabs were thought to have come from the Morrison Formation, but the rock and the footprints are very similar to those found in the underlying Summerville Formation; bar = 20 inches (50 cm); B. Pteraichnus tracks from the Sundance Formation of Wyoming, the equivalent of Utah’s Summerville Formation; bar = 4 inches (10 cm). A: based on Unwin 1989 and the original specimen; B: redrawn from Lockley and Hunt 1995.

that pterosaurs sailed through the skies of eastern withdrawing to the north, into Wyoming and Mon- Utah during the middle Jurassic on the basis of the tana. The low basin in east-central Utah was once Pteraichnus tracks. Most paleontologists regard the again exposed as habitat for terrestrial vertebrates. pterosaurs as well adapted to coastal environments, Rivers flowing from the adjacent highlands once where they fed on fish living in the shallow seas and again began to wash sediment into the basin, while lagoons. They could be considered the large “shore- plants started to carpet the surface of the lowlands. birds” of the Jurassic. It makes sense that the periph- As the end of the Jurassic period drew near and ery of Utah’s seaway would have been a suitable the seaway vanished, the dinosaur habitat in Utah habitat for them. greatly expanded. The stage was set for a dramatic The middle Jurassic seaway of central Utah was proliferation of dinosaurs and the creation of Utah’s the result of a temporary incursion of the seas from own Jurassic Park. the north. By about 160 million years ago it was Chapter 4 The Late Jurassic The Golden Age of the Sauropods 04 Utah State Highway 24 is one of the most scenic the undulating land, the highway crosses the San byways in the world. Immediately south of its junc- Rafael River bottom about 5 miles south of I-70. tion with I-70, 9 miles west of Green River, the rib- At this point the badlands begin to diminish as the bon of asphalt meanders south through stunning road continues south across the vast San Rafael badlands gouged from layers of soft rock of incan- desert country, sprinting for the Henry Moun- descent colors. The bald hummocks and barren tains looming on the distant horizon. Few travel- mounds almost shine with pastel bands of lavender, ers along this segment of Highway 24 can resist the brown, vermilion, and ocher, streaked with lay- temptation to stroll through the variegated won- ers of ashen gray (fig. 4.1). Rising and falling with derland along the highway, exploring the countless

4.1. Colorful outcrops of the Morrison Formation along Utah Highway 24, west of Green River. Courtesy John Telford.

75 76 Chapter 4 gullies and nooks cut into the soft rocks. An excur- sion out into these badlands almost always results in some interesting treasures: a rusty Prince Albert can with crumpled and yellowed claim papers from the uranium mining days, a rouge-colored rattle- snake slithering along a gully bottom until it disappears under a rock, or perhaps the disintegrating carcass of a 1948 pickup truck. Those who possess eyes tuned to things geological and who have the patience to look carefully will also find small fragments of fossil bone almost anywhere in these badlands. The fossil bone betrays the age and identity of the rock strata exposed in the etched hills. These picturesque knolls are the icons of the late Juras- sic Morrison Formation: the Dinosaur Graveyard of the West.

The Morrison Formation 4.2. Utah in late Jurassic time. The sediments of the Following the withdrawal of the middle Jurassic sea- Morrison Formation accumulated in a vast interior way in central Utah about 165 million years ago, the basin. The major dinosaur localities in the Utah region interior basin was once again exposed as land for are identified by number: 1. Morrison, Colorado; 2. Canon City, Colorado; 3. Dry Mesa–Potter Creek, Colo- the remainder of the Jurassic Period. Rivers flow- rado; 4. Grand Junction area, Colorado; 5. Cleveland– ing from the bordering ramparts collected within Lloyd Quarry, Utah; 6. Dinosaur National Monument, the basin again, as they had during the late Triassic Utah; 7. Hanksville–Burpee Quarry, Utah; 8. Rabbit Val- (Chinle). This time, however, the principal water- ley, Colorado; 9. Como Bluff, Wyoming; 10. Purgatoire River tracksite, Colorado. Reconstruction from Ronald sheds appear to have been the highlands to the Blakey/Colorado Plateau Geosystems, Inc. Used with west and to a lesser degree those in central Arizona permission. and southern Nevada to the southwest. The Meso- cordilleran High of earlier Jurassic time became much more prominent in the late Jurassic as wide- volcanic peaks that have long since been obliterated spread igneous activity elevated and enlarged the by erosion. In addition, across the Great Basin we ancient mountain system of western Utah and east- find good evidence of late Jurassic uplift produced ern Nevada. Many bodies of magma were emplaced by folding and crumpling of the earth’s crust under (primarily between about 170 and 140 million years enormous compressive forces (Allmendinger and ago) across the eastern Great Basin (Armstrong and Jordan 1984; DeCelles 2004; Dickinson 2006). Suppe 1973; Hintze 1988). Bodies of granite in the The upward rush of magma bodies, the eruption House and Deep Creek Ranges of western Utah, of volcanoes, and the compression of the eastern the Snake Range of eastern Nevada, and dozens Great Basin all served to hoist the Mesocordille- of other nearby localities record the surge of mol- ran High to unprecedented elevation. As the moun- ten rock from below. Almost certainly the Mesocor- tains rose, they became more effective in capturing dilleran High was further elevated by the explosive moisture from the late Jurassic clouds. Flowing eruption of some of this magma, forming a series of from enhanced watersheds and racing down steeper The Late Jurassic 77

4.3. The Morrison Formation of east-central Utah. Three subdivisions are recognized in most of the dinosaur country of central Utah: the Tidwell, Salt Wash, and Brushy Basin Members. Other members may be present elsewhere in Utah, particularly in the Four Corners region. slopes, the rivers draining the east flank of the into adjacent states throughout the Rocky Moun- Mesocordilleran High became the primary source tain region. The Morrison Formation is one of of both the water and sediment that was trans- the most widely distributed rock sequences in the ported into the lowlands of east-central Utah dur- world and is also one of the most intensely studied. ing late Jurassic time. As the rivers carried sediment In the 1950s rich uranium ores were discovered in from the highlands to the west, a vast alluvial plain the Morrison and Chinle Formations of the Colo- was constructed from the sediment grains depos- rado Plateau, triggering the great “uranium boom,” ited across the floor of the east-central Utah low- a notable chapter in the human history of eastern land. Layers of gravel, sand, and mud were spread Utah and western Colorado. The search for uranium out over 700,000 square miles of what is now Wyo- also brought a small army of geologists to the region ming, Utah, Colorado, New Mexico and Arizona to determine the origin of the ore bodies and to (fig. 4.2). These are the sediments of the Morrison investigate the controls on their distribution. Even Formation. today, after several decades of intensive mining, the The Morrison Formation was named in the late Morrison Formation is estimated to contain about 1800s for the small town of Morrison, Colorado, half of the uranium reserves of the United States about 20 miles southwest of Denver. This forma- (Peterson and Turner-Peterson 1987). Over the past tion was traced by geologists over hundreds of miles quarter-century as many as eight different members 78 Chapter 4

4.4. The Morrison Formation at Buckhorn Flat in the San Rafael Swell. The line separating the red beds in the lower slopes from the overlying tan ledges is the boundary between the Morrison Formation and the underlying Summer- ville Formation. Above this line, the Tidwell (soft grayish slope), Salt Wash (tan sandstone ledges), and Brushy Basin (soft pale purplish slopes) Members are exposed in the upper cliffs. Courtesy John Telford. have been established for the formation in the Col- Of course, the Morrison Formation has been so orado Plateau region. The numerous subdivisions well studied because it has produced literally tens of reflect the extreme heterogeneity of the Morrison thousands of dinosaur bones from dozens of sites sediments, a product of the largely fluvial and lacus- throughout the West. The Morrison Formation is trine processes of deposition. Three of these mem- one of the most prolific sources of dinosaur fossils bers are usually present in the dinosaur country of in the world. Unlike the earlier phases of dinosaur eastern and central Utah (in ascending order): the history in Utah, known only from scrappy fos- Tidwell Member, Salt Wash Member, and Brushy sil material and footprint evidence, the late Jurassic Basin Member (fig. 4.3). Elsewhere in the Colorado fossil record explodes into dazzling abundance. But Plateau, particularly in the Four Corners region before we review the rich dinosaur fauna from the and in northern Arizona, other members have been Morrison Formation, let’s explore late Jurassic land- identified that are less important to the story of scapes of Utah by examining the sediments in which Utah dinosaurs. the fossils are preserved. The Late Jurassic 79

The Tidwell Member is the oldest of the three dinosaur fossils ever discovered in Utah came from main members of the Morrison Formation recog- this member (Gillette 1993). It appears that the ter- nized in most localities in east-central Utah (fig. restrial habitats of central Utah during Tidwell time 4.4). This sequence of rock layers is usually between were not particularly well suited for large terrestrial 25 and 75 feet thick in eastern Utah but includes as animals or that conditions did not favor the fre- much as 300 feet of sediments in adjacent areas. The quent preservation of their remains or both. Tidwell Member is a soft, slope-forming unit con- Above the Tidwell Member throughout east-cen- sisting of a varied assemblage of sedimentary rocks tral Utah is a ridge- and bench-forming sequence including pale brown sandstone, red-gray mud- dominated by coarse, cross-bedded sandstone and stone, gypsum, and limestone (Peterson 1988). The conglomerate known as the Salt Wash Member of mudstones of the Tidwell Member sometimes con- the Morrison Formation. Its coarse-grained sed- tain hard nodules of reddish-orange chert, a micro- iments are relatively hard and more resistant to crystalline form of silica (SiO2). These chert nodules weathering than the softer rocks above and below are so brilliantly colored that they have become a them (fig. 4.4). The cross-bedding of sandstones favorite of rockhounds, who commonly refer to and orientation of pebbles in the conglomerates of them as “sunset agate.” the Salt Wash Member indicate deposition by swift The sediments of the Tidwell Member seem to rivers flowing mainly from the highlands to the west have been deposited on the poorly drained surface and southwest (Peterson and Turner-Peterson 1987). of a lowland basin. The limestone of the Tidwell The Salt Wash Member varies in thickness from Member commonly contains fossils of ostracods 150 feet to 300 feet in central Utah but thickens as (small aquatic crustaceans), charophytes (green it is traced to the west, providing further evidence algae common in bodies of fresh water), and gastro- of sediment transportation from that direction. The pods that indicate deposition primarily in lakes and sandstone and conglomerate in this member were ponds. The mudstones in the Tidwell probably rep- probably deposited by a complex braided river sys- resent fine silt and clay that accumulated along the tem that spread sand and gravel eastward from the edges of the lakes, on mudflats, or in swampy areas foothills of the Mesocordilleran High as a broad (Peterson and Turner-Peterson 1987). Most of the alluvial apron, sloping down from the western high- sandstones appear to have been deposited by rel- lands to the lower terrain in central Utah. As the atively small steams or, in places, as small patches many small braided streams descended from the of dune sand transported by wind. No evidence of western mountains, they eventually collected into large, vigorous river systems has been observed in fewer but larger meandering streams flowing across any of the Tidwell sediments. the more level ground in eastern Utah. The base of the Tidwell Member is marked by Many of the individual layers of sandstone in the a prominent and widespread unconformity, below Salt Wash Member are broadly lenticular, taper- which the beds of various formations of the under- ing laterally to thin edges and eventually disappear- lying San Rafael Group were beveled prior to the ing over distances ranging from several yards to deposition of Tidwell sediments. This unconfor- several miles. Between the lenticular sheets of sand mity signifies an extensive period of erosion follow- and gravel, or adjacent to their edges, greenish-gray ing the retreat of the middle Jurassic seaway from mudstone and clay-rich limestones are common in central Utah. The erosion probably occurred around the Salt Wash Member, particularly in easternmost 160 million years ago and may have persisted for Utah. These fine-grained components represent several million years. The Tidwell Member has sediments deposited during floods on the nearly produced only a few dinosaur bones, but the first flat surfaces separating the many river channels. 80 Chapter 4

Scattered throughout the Salt Wash Member and minerals such as analcime and clinoptilolite that sometimes mixed into the sandstone, conglomerate, are thought to have formed as volcanic ash reacted and mudstone are thin layers of bentonite, the clay- with the alkaline water of a large temporary lake rich rock derived from volcanic ash. The bentonite (Peterson and Turner-Peterson 1987). Such lakes are of this member was no doubt derived from the vol- known as playas and are particularly common in canically active highlands to the west, which would arid regions. The water in playa lakes gathers for a periodically have discharged great clouds of ash that short time after a period of heavy rain, but it soon drifted downwind over the low basin to the east. evaporates under the influence of a dry, desert- Dinosaur fossils have been found in the Salt like climate. As the lake diminishes through evapo- Wash Member at dozens of localities in Utah and ration, its water becomes more saline and alkaline. Colorado, but they are usually fragmentary skel- Eventually the water disappears altogether, leaving a etons or isolated bones. This probably reflects the blinding white lake bed behind, blanketed by a crust vigorous energy of the rivers that transported and of minerals precipitated from the vanished water. deposited most of sediments observed. Skeletal Around the edges of the playa the drying mud remains would most commonly have been disar- commonly shrinks to form an intricate network ticulated and scattered by the swift water or flood of cracks that can be preserved when the deposi- surges in such a setting. Only occasionally would tion of sediment resumes after the next cloudburst. relatively complete carcasses of dinosaurs be buried Mud cracks are not uncommon in some of the fine- intact and preserved as fossils. grained deposits of the Morrison Formation. From The youngest member of the Morrison Forma- the distribution of the minerals produced in such a tion in the northern and central Colorado Plateau playa basin in southwest Colorado, C. E. Turner and is the Brushy Basin Member. It consists mostly of others (1991) postulated that an enormous alkaline soft, slope-forming mudstone and shale interbedded lake existed in southwest Colorado during Brushy with less common limestone, coarse sandstone, and Basin time (fig. 4.5). This lake was some 300 miles conglomerate. Typically the dominant mudstones of long, comparable in size to modern Lake Michigan. the Brushy Basin Member are beautifully variegated, Many other (much smaller) playa lakes probably exhibiting pastel bands of purple and maroon, red dotted the low interior basin during the time when and gray, ocher and rose (fig. 4.1). These distinc- the Brushy Basin sediments were deposited. tive colors arise from the oxidation of metals such The coarse granular sediments of the Brushy as iron and manganese in the sediments. Layers of Basin Member are commonly arranged in lenticular volcanic ash, usually altered to bentonite, are fairly bodies representing the filled channels of rivers or common in the Brushy Basin Member. Some of the as broad but thin sheets of sand signifying floodwa- volcanic ash layers and bentonitic claystones con- ters surging from swollen rivers across the adjacent tain mineral crystals that can be dated by radio- floodplains. These coarse-grained deposits were metric techniques. These dates provide important deposited mostly by rivers that flowed from the west information on the absolute age of some dinosaur- or southwest in braided or winding courses. Many producing horizons. of the rivers eventually drained into low lake basins The mudstones were deposited in a variety of or valleys in the eastern portion of the Colorado low-energy sedimentary environments, including Plateau. the channels and muddy banks of sluggish rivers, The Brushy Basin Member is one of the most swamps and bogs, and shallow ephemeral lakes. In richly fossiliferous nonmarine sedimentary rock the eastern portion of the Colorado Plateau some of sequences in the world. Dozens of dinosaur bone the mudstones of the Brushy Basin Member contain quarries have been established in exposures of the The Late Jurassic 81

4.5. Central Utah during the time when the sediments of the Brushy Basin Member were deposited. An alkaline lake existed in southwest Col- orado. Reconstruction from Ronald Blakey/Colorado Pla- teau Geosystems, Inc. Used with permission.

Brushy Basin Member in Utah, Wyoming, Colo- 147 million years ago (Foster 2003). During this rado, and South Dakota. Most of the major dino- span of time the landscapes of east-central Utah saur quarries shown in figure 4.2 are situated in the evolved steadily in response to geologic events that strata of the Brushy Basin Member. Tens of thou- occurred both within the region and around the sands of bones have been excavated from these sites, periphery of the modern Colorado Plateau. From and many more remain locked within the sedi- the distribution of the various members of the Mor- ments. In Utah the Brushy Basin Member produces rison Formation, and from the variations in their truly spectacular concentrations of dinosaur bone thickness and composition, it appears that the at the Cleveland-Lloyd Quarry in Emery County, at earth’s crust in Utah and Colorado experienced Dinosaur National Monument northeast of Vernal, modest movements related to compressional forces and at the recently discovered Hanksville-Burpee that were transmitted inland from the western edge Quarry west of Hanksville (Kirkland 2009). Else- of North America. This compression caused some where scores of less impressive accumulations of areas of the Colorado Plateau to rise, forming uplifts fossils have been found in the Brushy Basin Mem- that affected the patterns of drainage for the late ber throughout east-central Utah. There is a good Jurassic rivers. chance of finding dinosaur bones or teeth virtually Between the elevated Mesocordilleran High on anywhere these soft mudstones are exposed. the west and the ancient Uncompahgre Highland to the east, the Zuni Uplift rose along the Arizona- New Mexico boundary, the Monument Uplift of The Morrison Landscape: A Land Alive southern Utah and northern Arizona was activated, The Morrison Formation probably encompasses and the Emery Uplift emerged in central Utah some 8 million years of the late Jurassic period, (Peterson and Tyler 1985; Peterson and Turner- from approximately 155 million years ago to about Peterson 1987). None of these crustal disturbances 82 Chapter 4 resulted in prominent mountain systems, but they low-angle fractures appropriately known as thrust were sufficiently high to direct the drainages of the faults. As the slabs were thrust to the east, they regions toward lower areas adjacent to them (fig. piled up like shingles on a roof to create an exten- 4.2). sive mountain belt in the eastern Great Basin. This While these structures were rising, other areas of ancient mountain system is known as the Sevier the Colorado Plateau were subsiding to form basins Orogenic Belt, a feature that was to become even in which unusually thick sequences of sediment more prominent in the Cretaceous. The late Jurassic accumulated as the streams converged toward the deformation was merely the first rumblings in the lowest points. The previously described playa lake Sevier Orogenic Belt. Nonetheless, powerful forces complex recognized in the Brushy Basin Member in began to elevate the Mesocordilleran High, already southwest Colorado developed in such a low basin. swollen from the volcanic activity that began mil- Elsewhere in the late Jurassic interior basin smaller lions of years earlier. The geological disturbances areas such as the Henry Basin of central Utah also linked to the Nevadan Orogeny thus resulted in foundered. The pattern of uplifts and basins shifted widespread geological havoc throughout western constantly through the time when sediments of North America. The relatively subtle basins and the Morrison Formation were being deposited. uplifts that formed in central Utah during the late The rivers draining the Morrison plain continually Jurassic are just a whisper of the chaos that was tak- shifted their locations and directions as small basins ing place elsewhere. The West was genuinely wild in became filled with sediment and new areas began the late Jurassic. What an exciting world the dino- to subside. The uplifted regions were soon reduced saurs enjoyed! by erosion, but many of them may have experienced The climate of Utah in the late Jurassic seems to later pulses of reactivation. The Morrison Forma- have been almost as riotous as the geologic envi- tion was thus deposited on a throbbing landscape, ronment. The gypsum, playa lake sediments, and continually rising in some places while sagging in scattered patches of eolian sandstone in the var- others. All of this geological ruckus was but a hint ious members of the Morrison Formation all of even more drastic events taking place beyond the seem to suggest generally arid to semiarid condi- Colorado Plateau region. tions throughout the time represented by this for- The late Jurassic was the time of the great Neva- mation (Parrish and others 2004; Rees and others dan Orogeny in western North America. This 2004). But the Morrison Formation has produced period of intense mountain building was related at least thirty-four genera of fossil plants (Tidwell to the convergence of great slabs of rock, known 1990). This floral assemblage is dominated by coni- as lithospheric plates, along the western edge of fers but includes many ferns, seed-ferns, cycads, the continent. As North America smashed into the and ginkgoes, all of which require abundant mois- leading edge of an oceanic plate moving to the east, ture. In places such as the Escalante Petrified Forest rocks were crushed, splintered, and forced upward State Park the striking abundance of plant fossils in to form the famous Franciscan complex of the Cal- the Morrison Formation indicates fairly dense clus- ifornia Coast Ranges. Inland from the coast the ters of vegetation composed of large conifer trees Sierra Nevada region was ablaze with volcanic activ- with an undergrowth of smaller shrublike plants. In ity and constantly shaken by earthquakes gener- addition, the great numbers of herbivorous dino- ated as the rocks fractured. Even in Nevada, western saurs preserved in the Morrison seem to suggest Utah, and Idaho, far inland from the zone of plate a large population of herbivores (many of gigantic convergence, the compressional forces were suf- size) requiring a prodigious food supply. The over- ficient to drive great slabs of rock eastward along all character of the Morrison flora is most similar to The Late Jurassic 83 the verdant forests that grow in the humid subtrop- lack of food and water during the droughts. Even- ics of today’s world, not in a dry desertlike environ- tually the rains returned, bringing the rebirth of life ment (Tidwell 1990). Moreover, in some places the as the cycle was renewed. Such a seasonal climate Morrison Formation also produces remains of fish, would have allowed for the profuse growth of vege- insects, and turtles that seem to represent semiper- tation during times of abundant moisture but would manent aquatic environments such as lakes, ponds, also have resulted in the dry intervals recorded by or swamps (Gorman and others 2008). A mysterious the gypsum, eolian sandstones, and mud-cracked paradox of the Morrison Formation is the apparent playa lake sediments observed in parts of the Morri- contradiction between environmental interpreta- son Formation. tions based on the rocks (dry climate) and those We know that in the modern world such strongly inferred from the fossil evidence (humid climate). seasonal climates can support large and diverse pop- At least one plausible, if not certain, explana- ulations of terrestrial vertebrates. The most obvi- tion for this intriguing conundrum exists. If the cli- ous example would be the savannahs of east Africa, mate of the Morrison basin was strongly seasonal which experience profound climatic oscillations in the late Jurassic, then periods of drought would between rainy intervals and scorching droughts. have alternated with periods of abundant moisture. The mammals of this area survive the droughts by In the rainy season the low basin received copi- migrating to less affected areas, by storing food ous runoff from the surrounding highlands. Dur- energy in the form of fat produced when food is ing such intervals the rivers flowing across the abundant, and by a remarkable array of behaviors uneven land would have been flushed and swol- designed to conserve water and energy. But there len. Many temporary lakes, large and small, would is one very important difference between modern have formed in low areas from impounded flood- Africa and Jurassic Utah: the primary food for most waters. For a few weeks or months following the herbivores in Africa is the grass that grows across floods the landscape would have become carpeted the vast plains. These grasses are well adapted to the with vegetation. In places, such as along the shores cyclic climate: they can persist in dormancy dur- of lakes and rivers, water may have been so plen- ing the droughts but sprout quickly when moisture tiful that small patches of forests might have been is available and grow rapidly. The vigorous regen- established. Eventually, however, the land dried out eration of the African grasses following droughts as the rainy season ended and the climatic cycle can provide a great amount of food for herbivo- passed into the drought stage. The Morrison plain rous mammals in a relatively short time. Thus the then lost its green blush as plants withered and died African grasslands recover swiftly from the dry from the lack of moisture. The surviving herbage season. But grasses are angiosperms and did not became concentrated along the banks of perma- develop until the end of the Mesozoic. No grasses nent streams and around the larger temporary lakes, existed in Utah during the late Jurassic. Many of where water supplies were still adequate. Many of the plants identified to date in the Morrison flora the lakes eventually disappeared completely, leaving do not appear to be very well adapted to dry cyclic parched lake bottoms mantled with a pallid crust of climates. Furthermore, the Morrison flora con- minerals such as gypsum. The dry lakebeds would sists mostly of tree- or shrub-sized plants that do have been encircled by a ring of scrawny stubs of not seem capable of carpeting the land with veg- dead plants. At the height of the drought cycle many etation the way modern grasses do. So what was of the riverbeds became dry, while the wind kicked the primary food source for the dinosaurs and up dust devils everywhere across the thirsty land- other herbivores? What type of plant was the eco- scape. Animals perished in great numbers from the logic equivalent of the modern grasses during the 84 Chapter 4 late Jurassic? We have no certain answers for these Once in a while the cracked and curled mud in questions. Perhaps the ferns or cycads of the Mor- the lake basins might have contained the fragmen- rison flora possessed reproductive mechanisms or tary skeleton of a fish, a victim of the drought. As growth rates different from those of the living rep- the landscape browned, the plant-eating dinosaurs, resentatives of those groups. Maybe the landscape larger and more mobile than other reptiles, would during times of abundant moisture was blanketed have been forced to migrate as the search for water by a “fern prairie” unlike anything that exists in the and food became desperate. Contrary to the older modern world. Other plants, unknown from the views on most dinosaurs, paleontologists are now in fossil record, might have provided a significant por- general agreement that even the massive sauropods tion of the food base for the Morrison ecosystem. were capable of extensive overland travel (Chure What is certain, given the stupendous number of 1983). As herds of sauropods, groups of camp- their fossils preserved in the Morrison Formation, is tosaurs (an ornithopod), and individual stegosaurs that the herbivorous dinosaurs in late Jurassic Utah moved across the land, many of them succumbed to found food—and plenty of it. the blistering drought. The rotting carcasses of the If the low undulating plain of central Utah was weaker animals dotted the endless plain as the wind seasonally arid and occasionally wet during the late blew veils of dust across the barren land. Along the Jurassic, then the animals that populated the basin larger stream courses, a little muddy water might probably would have migrated in rhythm with the still have been available. This water would have seasons, just as the mammals of modern east Africa attracted the migrant dinosaurs in great numbers. do. During wet cycles plants would have been abun- Dinosaur fossils sometimes occur in large concen- dant and the herbivorous animals would be dis- trations in the Morrison Formation. The gathering persed widely across the verdant countryside. of many animals around water sources during the Predators would roam throughout the region, feed- dry season may be part of the explanation for this ing on the feeble, young, or isolated herbivores. The pattern (more on Utah localities of this type later). rivers would have been brimming with water: croc- Predators would also have been attracted to areas odiles, turtles, and fish would have flourished dur- where the migrating herds of herbivores were gath- ing these times. Such aquatic vertebrates are known ered. It is easy to imagine the Morrison theropods from the Morrison Formation in Utah, but their fos- lurking behind a rise or watching the migrating sau- sils are mostly confined to specific strata and are not ropods and ornithopods from some overlook, wait- found distributed randomly throughout the various ing for an opportunity to strike. rock layers. As the dry season approached the rivers Recall that the Morrison Formation covers an would dwindle to trickles of water before vanish- area exceeding 700,000 square miles, stretching ing completely to leave dry streambeds behind. The from Arizona and New Mexico north to the Cana- aquatic vertebrates would perish in great numbers, dian border. This north-south distance, some 900 providing food for scavengers. On occasion a few of miles, corresponds to more than 13 degrees of lati- the bones of crocodiles or turtles or fish might have tude. It is likely that the dry season occurred in late become buried, producing the scant remains that are summer and early fall, which would have begun ear- known to occur in parts of the Morrison Formation. lier in the southern portion of the basin than far- The lakes and ponds would shrivel, becoming more ther north. Thus northward migrations during the alkaline as they lost water through evaporation, droughts would eventually have led the dinosaurs while retaining all the dissolved minerals. Eventually to more abundant water and vegetation. As the dry only the parched crust of minerals remained to mark conditions spread north during late Jurassic sum- the former existence of the lakes and ponds. mers, we might envision waves of dinosaurs moving The Late Jurassic 85 in that direction too. During the late winter and of which appear to have been moving through the spring, warm and moist conditions would develop area in groups or herds. These herbivorous dinosaur first in the south. The northward migration of the footprints are mostly arranged in groups of paral- dry season might have been reversed at that time lel and closely spaced trackways, apparently made of the year. We don’t know for sure what the breed- at the same time. The trackways of theropods are ing patterns of the Morrison dinosaurs might have rare at the Purgatoire River site, suggesting a pred- been, but it is certainly plausible to imagine a breed- ator-prey ratio of about 1:30. The relatively small ing season that would have coincided with the time number of predators suggested by this trackway evi- when resources were most abundant. Under such a dence is also characteristic of the mammal commu- scenario, reproduction would have been optimized nities of modern east Africa. In comparison with by establishing breeding grounds in places and the vast herds of migrating antelope, zebras, and times when food and other resources were easily wildebeests in that area, we observe comparatively found. Though it is impossible to verify the notion few lions, cheetahs, and hyenas. Similar propor- of two annual migrations for the Morrison dino- tions between dinosaur predators and prey seem to saurs from their fossil record, some evidence indi- have existed in western North America during the cates that such events really happened in the Utah late Jurassic. Of course we have no way of knowing region. why the dinosaurs were traveling along the edge of As we have already learned, dinosaur bone frag- the lake in southeastern Colorado during Morrison ments can be found virtually anywhere in the Mor- time. Perhaps it was just part of their daily routine. rison Formation. Well-preserved skeletons and Or the herds might have been wandering north- mass accumulations of fossils are less common, west during the annual summer-fall migration. At but scraps of fossil bone are found literally every- the very least the Purgatoire River tracksite dem- where in the Morrison strata, particularly in the onstrates that sauropod and ornithopod dinosaurs Brushy Basin Member. If the late Jurassic dinosaur did travel in herds and that these groups were mov- populations migrated twice a year (or more often?) ing in a specific direction. The dinosaurs that made across the alluvial basin, then individual dino- the trackways along the Purgatoire River were going saurs could have died just about anywhere during somewhere, for some reason. a typical year. The unusually broad distribution of By combining all the geological and paleontolog- preserved dinosaur bone is consistent with the sug- ical evidence it is possible to reconstruct the overall gestion of migratory behavior. In addition, pale- character of the Morrison alluvial plain in east-cen- ontologists have documented a number a dinosaur tral Utah. It was a low region, hilly in places, laced trackways in the sediments of the Morrison Forma- by small rivers flowing from the west across the ter- tion in Utah, Colorado, and adjacent states (Lock- rain in either sinuous or braided patterns (fig. 4.5). ley and Hunt 1995), including one of the world’s At a paleolatitude of 20–30 degrees north of the largest footprint assemblages along the Purga- equator, the late Jurassic climate was warm and toire River in Colorado (Lockley and others 1986). semiarid, subject to strong seasonal variations. At the Purgatoire River site, over a hundred track- Many temporary lakes developed during the wet ways have been documented from a single horizon season. The larger lakes may have been semiperma- in the upper part of the Morrison Formation. Most nent features of the landscape, holding water that of these tracks were made by dinosaurs moving to was heavily mineralized by the high rates of evap- the northwest along the shore of a large lake (Lock- oration. Vegetation was generally sparse, but along ley and others 1986). The trackways were made pri- the stream banks and lake margins and during the marily by sauropod and ornithopod dinosaurs, both moist climatic cycles it might have been relatively 86 Chapter 4 dense. Volcanic eruptions in nearby regions period- more pages than this book contains to review them ically produced clouds of ash that descended over all adequately. the landscape. Powerful earthquakes in the surrounding mountains repeatedly shook the region. Sauropod Dinosaurs of the Morrison Formation The ground vibrated for other reasons as well: across The late Jurassic is commonly referred to as the this basin, great herds of dinosaurs were constantly “Golden Age of the Sauropods” (see the appen- on the move in search of food, water, or mates. dix on dinosaur classification) because this group of saurischian dinosaurs is remarkably abundant and diverse in faunas of this age on a global scale. Dinosaurs of the Morrison Formation: In Utah and adjacent regions, this sauropod dom- A Magnificent Menagerie of Monsters inance is clearly reflected by the fossils excavated The dinosaur fauna of the Morrison Formation is from the Morrison Formation. Morrison fossils (or one of the richest and most diverse fossil assem- replicas of them) have been used in major museums blages in the world. It includes at least thirty-four throughout the world to construct skeletal mounts genera, some of which include several different that illustrate the general characteristics of this sub- species (Chure and others 2006). The number of order. The sauropods known from the Morrison dinosaurs known from the Morrison Formation Formation belong to at least four different families: continues to increase steadily, as new specimens are the Diplodocidae, Brachiosauridae, Camarasauri- still being discovered throughout western North dae, and Cetiosauridae. Let’s explore the Morrison America. The first dinosaur remains ever discov- sauropods family by family. ered in Utah were found in the Morrison Forma- tion in San Juan County in 1859 (Gillette 1993), and Family Diplodocidae new material has been turning up ever since. The The diplodocid sauropods are named after Morrison dinosaur fauna thus has been studied by a Diplodocus, a well-known member of the family. small army of paleontologists for about 150 years. A All diplodocids share some basic skeletal charac- great deal of what we know about dinosaurs in gen- teristics that are used to define the group and dis- eral is based on the examination of fossils collected tinguish them from other sauropod dinosaurs. The from the Morrison Formation in Utah. And yet we skulls of diplodocids are lightly built and relatively still have much to learn and many mysteries to solve long and slender, much like a horse’s skull. The teeth concerning the nature and history of Utah’s late were of simple peglike form and were confined to Jurassic dinosaurs. However substantial our knowl- the front of the mouth; the diplodocids did not pos- edge of Morrison dinosaurs appears to be, some sess “molars” or cheek teeth. The nasal opening in uncertainties will always await resolution. Under- all diplodocids is positioned high on the skull above standing the late Jurassic dinosaurs of Utah and the and a bit in front of the eyes (fig. 4.6). The elongated world in which they lived is a task that will never be necks of the diplodocids had at least fifteen verte- completed, because every new discovery prompts brae (these are called cervical vertebrae), compared new questions. In the discussion that follows we will to the ten to twelve vertebrae in the back (known as explore the Morrison dinosaur fauna on the basis of dorsal vertebrae). The vertebrae at the base of the the best available data, the existing fossils, and the neck and through the shoulder region have a deep current consensus among paleontologists on how V-shaped cleft in the diplodocids (fig. 4.7), pre- to interpret those data most appropriately. As in any sumably for the attachment of a large ligament that issue in paleontology, controversies concerning the helped to maneuver the neck. In the hip region, the Morrison dinosaurs abound. It would require many bones of the back had tall neural spines projecting The Late Jurassic 87

4.6. Skull of Diplodocus in side (left) and front (right) views. As in the case of all diplodocid sauropods, the skull is relatively long, narrow, and lightly constructed. Note that the teeth project slightly forward and were restricted to the front of the jaws. The nostrils were located high on the head, above and slightly in front of the eyes.

4.7. The divided neural spines of Diplodocus (top left) and Apatosaurus (top right) are characteristic of the family Diplodocidae. The chevron bones of the tail are 4.8. The sacral (hip) vertebrae of the diplodocid sauro- also uniquely split into a double-keeled shape (bottom pods have tall neural spines such as these from Apato- center) in diplodocid sauropods. saurus, seen in lateral (left) and posterior (right) views. upward from the main body (or centrum) of the uniquely forked into a double keel-like form in the vertebrae (fig. 4.8). These tall spines served to diplodocids (fig. 4.7), unlike the simple Y-shaped anchor the large muscles and ligaments in the hips blades typical of other sauropods. These atypical and rump of diplodocids. The long tails were con- chevrons in Diplodocus inspired the genus name, structed of as many as eighty individual bones (the which means “double beam.” caudal vertebrae). The last thirty or forty caudal ver- Diplodocus tebrae were slender and highly elongated, indicating Diplodocus was a large but relatively slender and that the tails of all diplodocids tapered to a whiplike lightly constructed sauropod. Though full-grown tip. Below the caudal vertebrae in the middle part adults may have attained lengths of 70–85 feet of the tail the small bones known as chevrons were (about 25 meters) and stood about 13 feet (about 4 88 Chapter 4

4.9. Reconstructed skeletons of Diplodocus (top) and Apatosaurus (bottom). Though these two sauropods were comparable in length, Diplodocus was more slender and lightly built than Apatosaurus. meters) high at the hip, they only weighed between Diplodocus appears to have been a gregarious 13 and 17 tons. As in other diplodocids, the skull was sauropod. In several Morrison localities the remains narrow and long with small pencil-like teeth pro- of many individuals are found clustered together. At jecting forward from the front of the mouth (fig. the Howe Quarry in northern Wyoming, for exam- 4.6). In most specimens of this dinosaur the teeth ple, at least nineteen individuals of Diplodocus are show little wear and were apparently not used for represented by the thousands of bones preserved chewing plant fodder. The nostrils opened high on in that location. It is likely that many individuals the head of Diplodocus, well above the eyes. The of Diplodocus roamed the Morrison plain in herds shoulders were lower than the hips (fig. 4.9); as containing both adults and juveniles. We can only in all diplodocids, the neural spines of the verte- speculate about the social behavior that might have brae in the shoulder region were divided by a deep existed in such Diplodocus herds. Was there a dom- V-shaped cleft. Three species of Diplodocus are rec- inant “bull”? Were the young placed in the cen- ognized as valid by most paleontologists: D. longus, ter of the herd for protection? How did individuals D. carnegii, and D. hayi (McIntosh 1990). A fourth in the herd communicate? For herding behavior species, D. lacustris, was based solely on a few teeth to be an effective survival strategy, some degree of and is probably a dubious name. D. longus was evi- social structuring seems necessary. We commonly dently the most common species in Utah, but D. observe such social organization in the modern carnegii has also been reported from the state. The world in the herds of large mammals such as ele- differences between the various species of Diplodo- phants, bison, and caribou. In fact it appears that cus are not dramatic. It probably would have taken these herds would collapse into chaos without such some close examination to tell them apart in Utah instinctive or “intelligent” group behavior. The evi- during the late Jurassic. dence for herding behavior in Diplodocus and other 4.10. A Diplodocus herd moving across the Morrison interior basin. Illustration by Carel Brest van Kempen. 4.11. Apatosaurus feeding on low-growing vegetation. The long neck may have allowed these sauropods to reach a considerable amount of plant food with only minor movement of the massive body. Illustration by Carel Brest van Kempen. The Late Jurassic 91 sauropods is strengthened by trackways such as plants covering a large area without having to con- those preserved at the Purgatoire River site and by tinuously reposition their bodies. We might envi- the broad distribution of sauropod remains in the sion Diplodocus feeding as it moved slowly and Morrison Formation. Though we cannot prove the infrequently, sweeping its head from side to side, notion, it certainly seems likely that the late Juras- while nipping the leaves of low-growing shrubs. sic dinosaur migrations in Utah involved the move- Once in a while it would raise the head to reach a ment of many groups of giant sauropods across the particularly succulent leaf, to scan the horizon for spacious Morrison basin (fig. 4.10). predators, or to check the position of the herd. The Diplodocus and many other sauropod dinosaurs elevated posture might also have been used to gain have long been considered high browsers, feeding access to higher food during droughts or when trav- on the foliage of large, tree-sized plants. The coni- eling through “overgrazed” areas. fers were probably the largest plants in the Morrison The small teeth of Diplodocus are shaped like flora, but the ginkgoes, cycads, and tree ferns grew simple pegs and generally show little sign of wear. to considerable heights as well. Some paleontolo- From this we can conclude that they were not used gists have questioned the idea that the sauropods to chew herbaceous food. Instead it appears that fed exclusively on the leaves of tall trees (Alexander the teeth were used primarily to rake vegetation 1985). Studies of the mechanics of sauropod necks into the mouth or to strip leaves from branches. (e.g., Parrish and Stevens 1995) indicate that the ver- The efficient digestion of plant material requires tical flexing of the neck was actually limited by the that it be pulverized somehow, so we might won- way the cervical vertebrae are positioned and inter- der how Diplodocus and its kin “chewed.” It is highly lock with one another. To illustrate this, make a probable that sauropods with such weak dentition fist with one of your hands and raise your arm so possessed some kind of accessory organ like a giz- that the back of your hand is level. Keeping your zard that was used to masticate food after it was fist level, extend your index finger and try to lift it, swallowed. In modern birds (and some reptiles as as if you were attempting to point toward the ceil- well) the gizzard is a muscular organ that contains ing. Note the angle made between your level fist and small stones swallowed by the animal. As the giz- your extended index finger. This angle roughly cor- zard muscles contract, the ingested food is ground responds to the maximum angle possible between into a pulp by the stones. Modern birds, particu- the body and neck of most sauropods. The diplodo- larly those that eat grain or seeds (such as the famil- cid dinosaurs could not elevate their necks to a iar barnyard chicken), require such an accessory vertical position. The tall neural spines in the hip organ because they don’t have teeth. The diplodo- region of the diplodocids suggest that they could cids had teeth, of course, but not many and they probably rear up on their hind limbs to gain a little were puny. We often find relatively large smooth, more vertical reach. Many specimens of sauropods rounded, and highly polished stones in exposures exhibit some fusion of the caudal vertebrae about of the fine-grained mudstones of the Morrison For- where the tail would have contacted the ground in mation in Utah. Because they are much larger than such a tripodial stance. So sauropods like Diplod- the silt and clay particles composing the mudstones, ocus could feed on high vegetation, but that was these stones were probably not deposited by the probably not the main function of their long neck. same low-energy streams that laid down the finer Instead the neck appears to have been more flexi- sediment surrounding them. These stones are often ble in a horizontal plane and could be swung from called gastroliths (“stomach stones”), suggesting that side to side in a wide arc. This motion would have they might represent the gizzard stones of sauro- allowed the diplodocids to reach the low-growing pod (or other?) dinosaurs. David Gillette has found 92 Chapter 4 gastroliths that are clearly associated with skeletal reconstruct the skeleton of the gigantic Bronto- remains of the giant diplodocid sauropod Seismo- saurus. Because many portions of it were missing, saurus in the Morrison Formation of New Mex- he had to make some guesses about the unknown ico. The clustering and alignment of the gastroliths parts. Marsh generally made good guesses, but from at the New Mexico locality suggest that Seismo- the various sauropod skulls that had been found saurus may have had two gizzardlike organs along in the Morrison Formation he picked one that was its digestive tract (Gillette and others 1990). In the very similar to Camarasaurus (discussed later in case of Seismosaurus the evidence for sauropod gas- this chapter). When Marsh’s reconstruction was troliths is fairly convincing, but often such stones complete, Brontosaurus possessed a stubby, com- are found scattered throughout the Morrison For- pact head unlike the slender elongated skulls typical mation, without an association with any skeletal of all diplodocids. The error went uncorrected for remains. Identifying the isolated stones in the Mor- many decades, and the popular images of the blunt- rison Formation as dinosaur gastroliths is somewhat faced Brontosaurus were disseminated all over the speculative, but it is likely that at least some of them world. Later studies revealed that the original fos- were regurgitated by passing sauropods or were left sils of Apatosaurus and Brontosaurus actually rep- over after the complete decomposition of a sauro- resented small and large individuals, respectively, pod carcass. of the same genus. The rule in paleontology is that Apatosaurus the first name applied to a genus is retained while Apatosaurus, a relative of Diplodocus within the subsequent names are regarded as synonyms and family Diplodocidae, is known from several differ- abandoned. The public had never heard of Apato- ent localities in Utah, Wyoming, and Colorado. It saurus, however, and the incorrect name Bronto- is also one of the most familiar sauropods to many saurus persisted in popular culture for years. Even people because of the popularization of so-called after the taxonomic error had been corrected we Brontosaurus, an inaccurate synonym for this genus, still had the problem of the wrong skull. It wasn’t over the past eighty years or so in the mass media. until the 1970s that this mistake was finally discov- Even today many adults remain confused by this ered. By carefully reviewing the original field notes tangled taxonomy, while children for some reason and quarry maps and by reexamining an isolated seem able to resolve the conflicting nomenclature sauropod skull found at Dinosaur National Mon- with greater ease. The story behind the confusion ument in Utah, David Berman and John McIntosh is a bit complicated, but it is worth repeating here (Berman and McIntosh 1978) finally identified the because it reveals some of the difficulties faced by correct skull for Apatosaurus. To this day the Apato- paleontologists studying the incomplete remains of saurus skull found at Dinosaur National Monument dinosaurs. is the only one known for this genus that is reason- It all started in 1877, when the illustrious Yale ably complete. The correct skull for Apatosaurus is paleontologist O. C. Marsh first coined the name clearly of the diplodocid type and indicates a close Apatosaurus for a partial skeleton of a juvenile sau- relationship between Diplodocus and Apatosaurus. ropod excavated from the Morrison Formation Camarasaurus, the true owner of the head originally near Garden Park, Colorado. Two years later Marsh placed on Brontosaurus, is a much different type of described the fragmentary remains of a much larger sauropod and is not placed into the family Diplodo- sauropod found at Como Bluff, Wyoming, as Bron- cidae. It is interesting to note that Brontosaurus is tosaurus. Neither specimen had an attached skull, only one of the inaccurate names applied to Apato- though fragmentary sauropod skulls were found saurus. Others include Atlantosaurus and Elosau- in nearby quarries. In 1883 Marsh attempted to rus, both of which were assigned to fragmentary The Late Jurassic 93 remains that probably represent Apatosaurus. The depth equal to the length of their necks, the water Greek language roots for Apatosaurus mean “decep- pressure would have prevented them from expand- tive reptile”—what an appropriate name! ing their lungs enough to force air down the long Apatosaurus was about the same length as trachea. Finally, the legs of Apatosaurus and other Diplodocus, approaching 75 feet (25 meters) in sauropods were extremely heavy and pillarlike and adults, but was much heavier, weighing in at some had thick pads of shock-absorbing cartilage where 35–45 tons (fig. 4.9). This bulky sauropod had fore- they joined. The foot bones were broadly splayed, limbs that were a little shorter than the hind limbs, and the feet had circular pads on the soles much giving the massive body a slight forward tilt. The like the feet of elephants. It is unlikely that the limbs long neck was constructed of fifteen cervical ver- and feet of sauropods would be designed this way if tebrae; those near the base of the neck had divided they were not used to support the massive bodies of neural spines similar to the posterior cervical ver- these dinosaurs on land. tebrae of Diplodocus (fig. 4.7). The neural spines Even though the evidence for fully terrestrial on the vertebrate in the hip region were undivided, sauropods is unequivocal, the placement of the nos- very tall, and massive (fig. 4.8). As in all diplodo- trils on top of the head of Apatosaurus (and Diplod- cids, the tail was long, consisting of up to eighty ocus as well) is an intriguing puzzle. Why didn’t vertebrae, and ended in a slender whiplike tip. Apa- the nose simply open at the tip of the snout as it tosaurus had a large claw on the “thumbs” (first does in many other dinosaurs? Some paleontolo- digit) of its forefeet. These claws probably helped gists (Bakker 1986) have suggested that perhaps the provide leverage to swing the front of the body from diplodocids possessed a proboscis of some sort like side to side while Apatosaurus fed on low-growing an elephant or a tapir. The nostrils open relatively vegetation by sweeping its neck back and forth close high on the skull in both of these mammals, and to the ground. the fleshy trunk is elongated and lined with power- The skull of Apatosaurus is very similar to that ful muscles. Elephants and tapirs use their trunks of Diplodocus, with an elongated muzzle, tiny peg- as a “hand” to manipulate food objects, to strip veg- shaped teeth at the front of the jaws, and nostrils etation, to transfer water into the mouth, and to placed high on the top of the head. The placement perform a variety of other tasks that require a pre- of the nostrils on the top of the skull of Apatosau- hensile appendage. No one is sure whether or not rus and other diplodocids led to the early but now the diplodocid sauropods had trunks, and we will discarded speculation that these sauropods were probably never know for certain. But if they did, it aquatic animals and used their high nostrils in con- would be hard to imagine a more bizarre face gar- junction with their long necks to breathe while the nishing the ends of their long necks. body remained submerged in lakes or ponds. The Both Apatosaurus and Diplodocus possessed “snorkeling sauropod” myth has now been laid to extremely long tails that tapered to a slender tip. rest by numerous studies (e.g., Coombs 1975) that The last dozen or so tail bones are very slender and have revealed problems with this perception. We shaped like simple rods. The tail tapers like an old- have abandoned the aquatic image for Apatosaurus fashioned bullwhip, so it is tempting to think of and its kin for many reasons. First, their necks could it being used in that manner as a defensive organ. not be raised vertically but were designed to be held Could the tail of Apatosaurus deter an attacking horizontally or inclined upward at a low angle. Sec- theropod, or a group of them, by snapping back ond, abundant footprint evidence suggests that the and forth along the ground? Could this whiplash sauropods were capable of efficient movement over have toppled predators by slapping their legs out dry land. Third, if sauropods were submerged to a from under them or delivering a painful snap to 94 Chapter 4 the body? Maybe, but this was almost certainly not was almost certainly dissimilar, so they probably the primary means of defense for Apatosaurus and did not compete much for food. In fact we might other diplodocids. Whenever predators attacked, even imagine Apatosaurus eating the softer fronds of the giant sauropods probably needed little else than ferns and leafy ginkgoes (fig. 4.11), while Stegosau- their great bulk for adequate defense. Modern ele- rus might have preferred the coarser cycads grow- phants do not appear to have any highly specialized ing in the same area. Perhaps the fellowship between defensive organs either, yet they have little to fear Apatosaurus and Stegosaurus had other dimensions from lions and other predators in their habitat. The beside the noncompetition for food. Some type of very size of a healthy adult elephant is usually all interaction between these two dinosaurs may have that is required to discourage a lion or pack of hye- allowed them to resist predators more successfully nas from assaulting such large animals. In addition, when they were together than when they were on the herding behavior of elephants extends the pro- their own. This is pure speculation, of course, but the tection of large adult size to the smaller and weaker fossil record does suggest a closer affiliation between individuals within the herd. The late Jurassic the- these two herbivores than between any other pair of ropods probably did not launch a full-scale attack Morrison dinosaur genera. on an Apatosaurus or Diplodocus herd any more Apatosaurus has four known species: A. ajax, often than a pride of lions surges into a group of A. excelsus, A. yahnahpin, and A. louisae. The dis- elephants, which is almost never. This is not to say tinctions among the various species involve differ- that sauropods were not occasionally on the menu ences in size and variations in the detailed anatomy for Morrison theropods. Young Diplodocus calfs, of skeletal elements such as vertebrae, limb bones, or perhaps an injured or elderly adult, would have and shoulder blades. All four species are based on been in great peril if they strayed too far from the incomplete specimens, so we can’t be positively cer- protection of the herd. In that case the whiplash tail tain that each species is actually a unique form, probably did little to thwart the striking carnivores. reproductively isolated from the other three. In any The theropods would have enjoyed an ample feast. case the species of Apatosaurus are all more simi- Apatosaurus fossils are rarely found in great lar than they are different; what I have said about concentrations in the Morrison Formation, how- the genus would apply equally well to all of them. ever. Unlike the herding Diplodocus, Apatosaurus If we could have visited the Morrison plain during seems to have been a more solitary dinosaur, mov- the late Jurassic, perhaps the differences between the ing around the Morrison terrain as isolated animals species of Apatosaurus would have been more obvi- or, at most, in small groups of two or three individu- ous to us than are the variations in their fossils. als. But there does seem to have been an association Barosaurus between Apatosaurus and Stegosaurus, the plated Barosaurus is the largest of the three most com- ornithischian described later in this chapter. In most mon Morrison diplodocids, though it is represented places where the bones of Apatosaurus have been by less complete fossil material than either Diplod- found in the Morrison Formation, fossils of Stego- ocus or Apatosaurus. Barosaurus was about 80 feet saurus also have been recovered. This association is (about 25 meters) long and stood more than 14 feet probably more than a coincidence. Both Apatosaurus (about 4 meters) tall at the hips. It possessed a rel- and Stegosaurus were probably solitary low browsers. atively slender build, however, much like Diplod- Where the low-growing shrubs grew in profusion ocus, and probably weighed 25–35 tons, a weight on the Morrison plain, both dinosaurs would have range not unlike the smaller but bulkier Apatosau- found plentiful food. The teeth of these two dino- rus. The most distinctive feature of Barosaurus was saurs are much different and their feeding behavior its extremely long neck, which composed about The Late Jurassic 95

4.12. Highly elongated cervical (neck) vertebrae, such as this one being excavated at the Hanksville-Burpee Quarry, are characteristic of Barosaurus. Photo by Frank DeCourten. half of its total length. While no complete necks of structure and size of the known caudal vertebrae, it Barosaurus have been discovered, it appears to have appears that Barosaurus had a somewhat shorter tail had the same number of cervical vertebrae as other than Diplodocus. diplodocids (fifteen). The lengthening of the neck Though Barosaurus remains seem to be rare in in Barosaurus was the result of the extreme elonga- the Morrison Formation throughout most of west- tion of the cervical vertebrae, which are about one- ern North America, this genus is relatively well third longer than those of Diplodocus (fig. 4.12). The represented at Dinosaur National Monument in slender limb bones of Barosaurus are so similar to northeast Utah and has also been identified in those of Diplodocus that they are virtually indistin- the Hanksville-Burpee Quarry in central Utah. In guishable. In fact Barosaurus may not be as uncom- addition to the numerous preserved skeletal ele- mon as we think: many isolated limbs bones that ments from Dinosaur National Monument, scien- have been identified as the remains of large indi- tists have discovered a natural impression of skin viduals of Diplodocus may actually belong to Baro- in the sandstone that surrounded some of the Baro- saurus. Unless the limbs are found with portions of saurus fossils. The impression reveals a skin that the distinctive neck, it would not be easy to tell the was knobby with many prominent folds, like the difference between a large Diplodocus and a small skin of the modern gila monster (Heloderma suspec- Barosaurus. The tail of Barosaurus probably tapered tum), a large lizard from the American Southwest. to the whiplash tip typical of other diplodocids, but This fossil skin impression demonstrates that Baro- only the front half of the tail is known. Based on the saurus, and probably most other dinosaurs as well, 96 Chapter 4 possessed a coarse granular integument much dif- belonging to this genus and species has been ferent from the scale-covered skins of most living unearthed since the original discovery. The forelimb reptiles. of Dystrophaeus is rather slender, as in Diplodocus, Barosaurus was a highly successful sauropod and the foot bones are of a generalized diplodocid during the late Jurassic, in spite of the apparent scar- type. It may be that Dystrophaeus is actually a spe- city of its fossils in the Morrison Formation. Fos- cies of Diplodocus, but additional material will have sils of this dinosaur also have been discovered in to be found before we can be sure. The question may the famous Tendaguru Formation (also late Juras- be resolved soon, as Utah state paleontologist David sic) of Tanzania, indicating that it occupied an enor- Gillette has begun a study of some addition fos- mous geographic range. Even though western North sils recovered from Newberry’s original site in 1989 America was closer to Africa in the Jurassic period (Gillette 1993). than it is now, Barosaurus still must have roamed Outside of Utah several other diplodocids or over an immense tract of land covering at least sev- diplodocidlike sauropods have been found in the eral thousand miles. As we shall see later in this rocks of the Morrison Formation. These dinosaurs chapter, Barosaurus is not the only Morrison dino- roamed over great distances, so they most likely saur to surface in Africa. There appear to have been occupied portions of Utah even though their fos- few barriers to the dispersal of dinosaur populations sils have not yet been positively identified from between North America and Africa during the time localities within the state. Amphicoelias is one such when the Morrison and Tendaguru Formations Morrison dinosaur described by Cope (1877) from were being deposited. Colorado. Diplodocid remains from Montana expo- Other Morrison Diplodocids sures of the Morrison have also been identified as Aside from Diplodocus, Apatosaurus, and Baro- Amphicoelias. This genus is known on the basis of saurus, the Morrison Formation has produced extremely fragmentary fossils representing a por- remains of several other diplodocid dinosaurs or tion of the shoulder, forelimb, pelvis, and two ver- at least sauropods that seem to be closely related to tebrae from the back. Amphicoelias is very similar this family. None of these miscellaneous diplodo- to Diplodocus and may actually be a member of that cids are represented by material that is sufficiently genus (Foster 2003). Supersaurus (Jensen 1985a), complete to allow us to develop any comprehen- known from the Morrison Formation of western sive reconstructions of their anatomy. Nonethe- Colorado, was apparently an enormous diplodo- less, what we do know about them suggests that cid sauropod, close to 125 feet (about 40 meters) some were very impressive creatures. The fragmen- long and weighing some 50 or 60 tons. Supersau- tary remains also expand the known diversity of rus is known only from several pelvic bones, about the family Diplodocidae beyond the three genera a dozen caudal (tail) vertebrae, a few dorsal (back) described thus far. vertebrae, and a scapulocoracoid (equivalent to the Dystrophaeus was the first dinosaur ever discov- shoulder blade [scapula] and collar bone [clavicle] ered in Utah. A portion of the forelimb and a few of humans). In Supersaurus the scapulocoracoid was bones from the front foot were found by John S. over 8 feet (2.5 meters) long! Supersaurus is most Newberry in 1859 as he accompanied the Macomb similar to the diplodocids among all known sau- Expedition through southeastern Utah (Barnes ropod dinosaurs, but its placement into the family 1990). In 1877 these fossils were studied by the Diplodocidae is not absolutely certain. famous dinosaur paleontologist Edward D. Cope, Another gigantic late Jurassic diplodocid was who applied the name Dystrophaeus viaemalae to discovered by David Gillette in New Mexico and them. Unfortunately very little additional material named Seismosaurus halli. This large sauropod is The Late Jurassic 97 known on the basis of a single partially articulated skeleton consisting of more than thirty vertebrae from the tail, sacrum, and back along with portions of the pelvis, chevron bones, and some ribs (Gil- lette 1991). The tall neural spines of the sacral vertebrae and the divided neural spines of the vertebrae from the back are the clearest indications that Seis- mosaurus belongs to the family Diplodocidae. Other aspects of its anatomy, however, differ from those of the more common members of that family. The pelvis of Seismosaurus is more massive than that of other diplodocids, and the individual bones that compose it have more robust form. The caudal (tail) vertebrae are heavier than in other diplodocids and have neural spines that are nearly erect, as opposed to those of Apatosaurus and Diplodocus, which slant somewhat to the rear. Seismosaurus appears to have 4.13. The spatulate teeth of Camarasaurus (left) in comparison to the peglike tooth of Diplodocus (right). Note been around 120 feet (40 meters) long; the heavy the curving, spoonlike shape of the Camarasaurus tooth construction of its pelvis and tail suggests a sauro- and the large wear surface on the crown. Scale bar = 0.4 pod of impressive mass, perhaps 40 or 50 tons. No inch (10 mm). Seismosaurus remains have yet been found in Utah, but it almost certainly accompanied the herds of other sauropods as they moved about the broad alluvial plain of Morrison time.

Family Camarasauridae The camarasaurid sauropods are generally smaller but bulkier than the diplodocids. In addition, the skulls of the Camarasauridae are rather heavy and blunt in comparison to the lighter skulls and elongated snouts of the diplodocids. Perhaps the most important characteristic of the Cama- rasauridae in understanding their habits and 4.14. Skull of Camarasaurus. The large nostrils (en for behavior is their teeth. Unlike the feeble teeth of external nares) opened well above and in front of the the diplodocids, camarasaurid teeth are large and eyes in this blunt-faced sauropod. robust, shaped somewhat like a spoon, and bear relatively large wear surfaces (fig. 4.13). These den- typify the family Camarasauridae include a rela- tal features suggest that the camarasaurids made tively short neck consisting of about twelve cervi- much greater use of their teeth to process plant mat- cal vertebrae, neural spines divided by a U-shaped ter than did the diplodocids. The nostrils of cama- trough, relatively low neural spines rising from rasaurids are placed high on the skull as in the the sacral vertebrae in the hip region, and fore- diplodocids but are much larger and usually located limbs that are somewhat longer in relation to the a little farther forward (fig. 4.14). Other features that hind limbs than in the Diplodocidae. The forefeet 98 Chapter 4 of the camarasaurids were less splayed than those The skull of Camarasaurus is large and massive of the diplodocids, as the elongated foot bones were but not very long. The lower jaw is particularly heavy arranged in an arc rising from the base of the toes and expands toward the front. The snout and lower toward the “wrist” and ankle. The tails of cama- jaw are both strongly curved, giving Camarasau- rasaurids were relatively short and thick, consisting rus its unique brusque snout (fig. 4.14). The nostrils of about fifty or so vertebrae below which simple, of Camarasaurus are very large in comparison to bladelike chevron bones were suspended. those of the diplodocids, are located high above the The family Camarasauridae seems to be a less eyes and well in front of them, and open outward to diverse assemblage of sauropods than the Diplodo- either side of the skull. The spoonlike teeth of Cama- cidae. Only two or three North American genera rasaurus are comparatively large and are positioned can be confidently placed in the Camarasauridae. along the entire margin of the jaws. The large teeth Several other camarasaurids are known from other commonly exhibit prominent wear surfaces pro- continents. Though they may be less diverse than duced when the upper and lower teeth contacted the diplodocids, the camarasaurids, particularly the each other during chewing. The teeth are firmly set namesake genus Camarasaurus, are by far the most into sockets along a deep groove in the jaws. common dinosaur found in the Morrison Forma- The skeleton of Camarsaurus (fig. 4.15) is of typi- tion. Russell (1989) has estimated that about one of cal sauropod form but is proportioned much differ- every five dinosaur bones ever recovered from the ently than in the diplodocids. The neck, consisting Morrison sediments belongs to Camarasaurus. of only a dozen or so vertebrae, is shorter and more Camarasaurus corpulent than the slender neck of Diplodocus. The Camarasaurus was a medium-sized sauropod, cervical vertebrae of the neck, as well as the bones about 50 feet (about 15 meters) long, that stood elsewhere in the spinal column, have deep side some 12 feet (4 meters) high at the hips and prob- pockets known as pleurocoels. Many dinosaurs have ably weighed between 25 and 30 tons as a mature these weight-saving cavities, but they are particu- adult. The remains of Camarasaurus are remark- larly well developed in Camarasaurus. The tail is ably abundant in the Morrison Formation of Utah also short and relatively blunt. In some specimens and adjacent states. Consequently Camarasau- of Camarasaurus the caudal vertebrae in the for- rus is perhaps the best-known sauropod dinosaur ward portion of the tail are fused together into a in the world. As our knowledge of its anatomy has solid mass of bone (Rothschild and Berman 1991; developed over the past century, some of the earli- fig. 4.16). This condition would have resulted in a est sauropod remains described from the Morrison pronounced stiffening of the tail just behind the Formation, such as Morosaurus and Uintasaurus, rump. That suggests that the relatively short tail of are now known to be specimens of Camarasaurus. Camarasaurus was carried high above the ground, The number of Camarasaurus fossils known to sci- at least for those individuals that exhibit the fusion ence is large, probably in the thousands, allowing of caudal vertebrae. A similar fusion of caudal ver- paleontologists to make some very detailed recon- tebrae is sometimes seen in Diplodocus (Rothschild structions of this dinosaur. At least three different and Berman 1991). Contrary to some popular depic- species of Camarasaurus have been identified from tions, no strong evidence indicates that either of the Morrison Formation, differing slightly from these sauropods habitually dragged its tail behind it each other in body proportions and minor anatom- like a dead snake. Because the caudal vertebrae are ical details. Nearly all Utah specimens have been fused in only some specimens, this feature might identified as Camarasaurus lentus, and the following be linked to the sex of the dinosaur. It seems plau- discussion is based on this species. sible that males might have possessed the stiffened The Late Jurassic 99

4.15. Skeleton of Cama- rasaurus, approximately 50 feet long, as reconstructed by Gilmore 1925.

4.16. Fused caudal vertebrae of Camarasaurus. Two separate tail bones are joined by the growth of bone tissue around the point of articulation. Scale bar = 4 inches (10 cm). Based on photograph from Rothschild and Ber- man 1991.

4.17. The Y-shaped chevron bones from the tail of tail for defense against predators and competition Camarasaurus in rear (left) and side (right) views. Com- for mates, while the more flexible tails of females pare with figure 4.7, which shows the chevron bones might have been better suited for reproductive pos- from diplodocid sauropods. turing and egg-laying. The chevron bones in the tail of Camarasaurus, as is the case in all cama- metacarpals and metatarsals, fore and aft), however, rasaurids, are bladelike and divided at the upper were more elongated than in the diplodocids and end where they join the caudal vertebrae (fig. 4.17). were arranged in an arcuate pattern between the Camarasaurus forelimbs are longer in relation to toes and the ankles (or “wrists”). the hind limbs than are those of the diplodocids. One of the most complete dinosaur skeletons This difference in forelimb/hind limb proportions ever discovered was excavated in the early 1900s at is reflected in the nearly level positioning of the Dinosaur National Monument. This famous find is back of Camarasaurus, as opposed to the slight for- the skeleton of a juvenile Camarasaurus and is one ward slope along the backs of most diplodocids. The of the most notable dinosaur treasures collected in hind foot of Camarasaurus had five widely splayed Utah. The young Camarasaurus was only about 17 toes; the innermost toe was the largest and bore a feet (about 5 meters) long, less than half the normal large curved claw. The bones of the middle feet (the adult length of this genus. Remarkably, 90 percent 100 Chapter 4

doubt have been able to withstand powerful crushing forces that would have snapped the delicate teeth of Diplodocus. A. Fiorillo (1991) microscopi- cally examined the wear surfaces of Camarasaurus teeth and found coarse scratch marks and pits, indicating that relatively tough plant material was processed by them. Unlike the diplodocids, which used their teeth primarily for raking vegetation into the mouth or stripping it from branches, Camarasaurus probably chewed leafy food more thoroughly before passing it through the digestive tract. Although the neck was relatively short, it was flexible. Cama- rasaurus could probably have lifted its head a little higher than was comfortable for the diplodocids. Given the differences in their teeth, body size, and posture, it is highly doubtful that Camarasaurus competed with the diplodocids for the same food 4.18. Head and neck of the remarkably complete skeleton of a juvenile Camarasaurus from Dinosaur National resources. Camarasaurus more likely was a high Monument. browser and fed by nipping off the fronds of tree ferns or the leaves of cycads that grew well above of the skeleton was preserved and most of the bones the ground (fig. 4.19). This arborescent vegetation were still articulated (fig. 4.18). The small Cama- may have been tougher and more fibrous than the rasaurus must quickly have become buried follow- lower-growing shrubs that provided the bulk of the ing its premature death, for the remains show little diplodocid diet. Based on the overall abundance sign of scavenging, decomposition, or postmortem and geographic distribution of Camarasaurus and transportation of the bones in this extraordinary the diplodocid sauropods in the Morrison Forma- specimen. The fossils at Dinosaur National Mon- tion, they certainly appear to have been compatible ument are preserved in a lens of sandstone in the companions who romped together across the broad Brushy Basin Member that accumulated as a sandbar alluvial plain. in a river channel. The sandstone body, about 15 feet There seems to have been considerable varia- thick, has at least three bone-producing horizons tion among Camarasaurus during the late Jurassic. (Lawton 1977). A. R. Fiorillo (1994) has suggested At least three species of Camarasaurus populated that the bones in these horizons were buried over a the Morrison habitat in western North America: C. relatively short period, perhaps only a few months. supremus, C. grandis, and C. lentus. Remains of C. The remarkable specimen of the juvenile Cama- supremus were first found near Garden Park, Col- rasaurus from Dinosaur National Monument prob- orado, and indicate a massive animal with a femur ably arose from the nearly immediate burial of the nearly 6 feet (2 meters) long. C. lentus is extremely carcass soon after the death of the baby sauropod. common at Dinosaur National Monument and was The young camarasaur must have died very close to very similar to C. supremus except for its smaller or perhaps even on the sandbar in the river channel. size. C. grandis is also fairly common in Utah and Camarasaurus obviously was adapted to feed differs from the other two species in several ana- on different kinds of plants than those that sus- tomical details of the vertebrae from the back- tained the diplodocids. The robust teeth would no bone. A fourth species, C. lewisi, was described by 4.19. Camarasaurus mother and young feeding along the banks of a late Jurassic Utah stream. Illustration by Carel Brest van Kempen. 102 Chapter 4

a pronounced upward tilt from the hips to the shoulders. This limb structure, coupled with the extremely long necks, made the brachiosaurids look much like overgrown reptilian giraffes (figs. 4.21 and 4.22). Because of this unique form, the forelimb of the brachiosaurids carried much more weight than those of other sauropods. Consequently the front legs are massive and columnar, proportioned much like the forelimbs of an elephant. The shoulder girdle of brachiosaurids, which transmitted the weight of the body to the elephantine forelimbs, was more massive than in most other sauropods. In addition, 4.20. Skull of Brachiosaurus. Note the very large nos- the front feet are well designed to support the enor- tril (en) located high on the skull. The smaller opening below the nostril is the antorbital fenestra (aof). The mous load that they carried. The toes were formed teeth are large and chisel-shaped in the brachiosaurid from massive bones and were widely spread to dis- sauropods. tribute the immense weight, which may have totaled as much as 50 tons. The middle foot bones (meta- McIntosh and others (1996) on the basis of unique carpals) were very long and positioned almost ver- fossils that were originally thought to indicate a sep- tically to resist the crushing forces applied to them. arate genus, Cathetosaurus. Thick pads of shock-absorbing cartilage were present in the soles of the feet and between the limb Family Brachiosauridae bones to cushion the pounding that would have The family Brachiosauridae includes some of resulted from the movement of such large beasts. the most immense land animals that ever lived on The brachiosaurids were truly ponderous creatures; the earth. These gigantic sauropods had relatively the largest of them would have made Camarasaurus long skulls, not unlike those of the diplodocids, but look runty in comparison. with large bulging nostrils placed high on the face, In general brachiosaurids are very uncommon in a feature somewhat reminiscent of the camarasau- the Morrison Formation of western North Amer- rids (fig. 4.20). The teeth of the brachiosaurids were ica. No brachiosaurids remains have yet been rec- large, lining the entire margin of the jaws, and had a ognized among the fossils collected from Utah unique chisel-like form. The thirteen cervical verte- exposures of the Morrison Formation, but they are brae were highly elongated, giving the brachiosau- known from localities in western Colorado. The rids the longest necks of any dinosaur. The neural Grand Valley and Uncompahgre Plateau regions of spines of the cervical vertebrae were not bifurcated; Colorado, only 30 miles or so from the Utah bor- each vertebra possessed very long ribs that extended der, are among the few places in North America along the lower neck, probably to anchor large neck where brachiosaurid remains have been discov- muscles and ligaments. The tails, in contrast to the ered. Moreover, several different types of brachio- enormous necks, were relatively short and strongly saurids are represented among the Morrison fossils tapered. excavated from that region. Brachiosaurus altithorax Perhaps the most distinctive feature of the bra- was first identified from Morrison exposures near chiosaurids was the unusual proportions of their Grand Junction, Colorado, in the early 1900s (Riggs limbs. The forelimbs were significantly longer than 1903, 1904). In more recent years several other bra- the hind limbs, giving the relatively short back chiosaurids have been uncovered at the nearby Dry The Late Jurassic 103

4.21. The skeleton of Brachiosaurus. The long forelimbs lifted the shoulders well above the hips, giving this sauropod its unique giraffelike appearance. The long neck angled upward, allowing the brachiosaurids to feed on vegetation some 50 feet above the ground. Based on reconstruction of Norman 1991.

1985b; Miller and others 1991). Included in the more recent discoveries is the enormous brachiosaurid originally named Ultrasaurus but later renamed Ultrasauros. The bones on which the identification of Ultrasauros is based indicate a very large animal, exceeding 100 feet (33 meters) in length and weighing more than 125 tons! Although most paleontologists now consider Ultrasauros an invalid genus because the bones that define it appear to be a mixture of more than one dinosaur, it still provides evidence of extremely large brachiosaurids in the Utah region. Even the better-known Brachiosaurus was considerably larger than most of its sauropod contemporaries, reaching a length of around 75 feet (25 meters). The long necks of the brachiosaurids, coupled with their giraffelike stance, would have allowed them to raise their heads 45 feet or more above the ground. The unique anatomy of the brachiosaurid sauropods seems to suggest that these sauropods were especially well adapted to the niche of a high 4.22. Brachiosaurus, with its high nostrils and robust teeth, in the high canopy of the Jurassic forests. Illustra- browser. No other dinosaur could have competed tion by Carel Brest van Kempen. with them for the foliage crowning the tallest of the Jurassic trees. The brachiosaurids were clearly very Mesa Quarry in the Uncompahgre Plateau by scien- successful in this ecologic niche, for their remains tists from Brigham Young University (Jensen 1985a, have been found in North America, east Africa, and 104 Chapter 4

Europe. It seems that wherever tall trees existed in dinosaur community that existed in the Utah region the late Jurassic brachiosaurid sauropods were prob- during the late Jurassic, in spite of their rarity. ably nipping at their highest leaves. This provides a partial explanation for why the remains of bra- Family Cetiosauridae chiosaurids are unknown in Utah but do occur in The cetiosaurids represent a small group of rela- nearby western Colorado. As we have seen, during tively unspecialized sauropods. This family includes the late Jurassic most of eastern Utah was occupied fewer genera than either the Diplodocidae or the by the lowland basin in which the Morrison sedi- Brachiosauridae, and paleontologists are still uncer- ments were deposited. In western Colorado, how- tain about the precise relationships among the var- ever, the low terrain probably rose to the east toward ious types of cetiosaurs. In general the cetiosaurs small “islands” of higher ground that represented are a rather poorly defined group of moderate-sized the eroded remains of the late Paleozoic/early Meso- sauropods. The neural spines on the vertebrae of the zoic Uncompahgre Uplift. Though we have no geo- back and neck are undivided and possess relatively logical evidence that western Colorado was actually simple, oval pleurocoels. The necks appear to have mountainous during this time, the hilly terrain in been relatively short. The neural spines of vertebrae that region was likely to have been several hundred in the back region have flanges of bone (the trans- (or thousand?) feet higher than the lower portions verse processes) that extend outward and upward of the Morrison basin to the west in Utah. At these to connect with the heads of the ribs (fig. 4.23). In higher elevations, where water was more plentiful, the plant communities may well have been dominated by taller treelike ferns, ginkgoes, and conifers. Such habitats would have been preferred by the brachiosaurids, if we are correct in interpreting their overall anatomy as a reflection of their high- browsing habits. Any brachiosaurid that might have wandered to the lower ground in Utah would have found less food available and would have had to compete with the lower-browsing diplodocids and camarasaurids for it. Thus the scarcity of brachiosaurid remains in the Morrison Formation of Utah may be the result of the restriction of brachiosaurids to the loftier settings of the surrounding highlands. This hypothesis might be verified if brachiosaurid remains could be found in western Utah and eastern Nevada, where highlands similar to those of western Colorado are thought to have existed during the late Jurassic. Unfortunately, however, sedimentary rocks of late Jurassic age have not been found in that region. For the time being our explanation must remain a plau- 4.23. Dorsal vertebrae of Haplocanthosaurus. Lateral flanges of bones (the transverse processes) extend out- sible but unverified notion. Nonetheless, the bra- ward and upward from the vertical neural spines on the chiosaurids were probably an important part of the vertebrae from the back. Based on specimens illustrated in McIntosh and Williams 1988. The Late Jurassic 105 comparison to other sauropods, this configuration Camarasaurus. If that was the case, then we might of the transverse processes is one of the few dis- interpret the rarity of Haplocanthosaurus in Utah tinctive characteristics of the cetiosaurs. The neu- exposures of the Morrison Formation as a reflec- ral spines of the vertebrae in the hip region are low, tion of the superior adaptations of Camarasaurus as in the Camarasauridae, and the caudal vertebrae to a similar ecological niche. In many ways Hap- are relatively short and of simple form. Few skulls locanthosaurus was a primitive holdover during of cetiosaurs are known, but the animals appear to the late Jurassic, a “living fossil” in its time. If we have had spatulate teeth that were smaller and less could return to late Jurassic Utah, we might notice massive but more numerous than those of the bra- an occasional Haplocanthosaurus among the herds chiosaurids or camarasaurids. The limbs are mas- of sauropods. It would have been very rare, and we sive, as in all sauropods, but they do not appear to might be tempted to bestow “endangered species” be especially distinctive or specialized in any of the status on it—and endangered it was, for Haploc- known cetiosaurs. The cetiosaurs were fairly com- anthosaurus was the last known survivor of its lin- mon worldwide during the early Jurassic, but they eage. After the late Jurassic Haplocanthosaurus and seem to have become less abundant in the late Juras- all other cetiosaurids (as well as many other sauro- sic, when the more specialized brachiosaurids, pods!) vanish from the fossil record. diplodocids, and camarasaurids developed. Haplocanthosaurus is the only cetiosaur known Other Morrison Herbivores: The Ornithischians from the Morrison Formation (McIntosh and Wil- liams 1988; Foster 2003). The placement of Haplo- The great sauropods were no doubt the primary canthosaurus into the family Cetiosauridae is a bit herbivores during Morrison time, but other plant- speculative, but this dinosaur certainly does not eating dinosaurs are represented by the fossils exca- exhibit the distinguishing features of any other sau- vated from this formation. The miscellaneous ropod family. Haplocanthosaurus is most common herbivores all belong to the order Ornithischia and in the Garden Park area of Colorado, where at least include the plated stegosaurs, the bipedal ornitho- two different species have been identified, H. priscus pods, and the armored ankylosaurs. None of the and H. delfsi. Fragmentary remains of a sauropod ornithischian dinosaurs known from the Morrison that may represent Haplocanthosaurus have been Formation rivals the great sauropods in abundance collected in Utah from the Morrison Formation at or diversity. Nonetheless, they are all fascinating the Cleveland-Lloyd Quarry in Emery County. In creatures in their own right and warrant more than addition, some of the many isolated sauropod bones a passing mention. found in numerous other sites in Utah may be from Haplocanthosaurus. While the evidence of Haploc- Suborder Stegosauria, Family Stegosauridae anthosaurus in Utah is admittedly weak, it at least The stegosaurids are one of the most familiar of suggests that this sauropod might have lived among all late Jurassic ornithischian dinosaurs. No set of the far more common camarasaurids and diplodo- dinosaur toys has ever been produced that didn’t cids during the late Jurassic. include the familiar Stegosaurus, with its arched Haplocanthosaurus was not a large sauropod. back bristling with triangular bone plates. The A fully grown adult was probably about 45 feet (15 basic architecture of the stegosaurids has inspired meters) long and weighed something like 8 tons. numerous mythical monsters in science fiction The short neck and the general form of its teeth movies for decades. I for one have always been suggest that Haplocanthosaurus may have fed on impressed with the creativity of the originators of the same vegetation, and in the same manner, as the Godzilla movies: they managed to superimpose 106 Chapter 4

4.25. The small teeth of Stegosaurus. Scale bar = 0.16 inch (4 mm).

elongated, small, and narrow, with the eyes set well back toward the rear of the head (fig. 4.24). The teeth are small and of very simple leaflike form (fig. 4.25). The stegosaurids were exclusively quadru- 4.24. Skull of Stegosaurus. The low, narrow skull of pedal herbivores and were mostly medium-sized, Stegosaurus was about 18 inches long and tipped in life rarely exceeding 25 feet (7.5 meters) in length. with a sharp-edged beak. Redrawn from Gilmore 1914. Stegosaurus Stegosaurus is one of the best known of all stego- the characteristics of stegosaurs, theropods, and saurids and was the most widespread and abundant sauropods to come up with a fire-breathing carni- armored dinosaur in North America during the vore, as large as a skyscraper, that hauled an impres- late Jurassic. The skull of Stegosaurus was relatively sive array of plates and spikes along its back. The small in proportion to its body size and was long, stegosaurids, of course, were the basis for that trait narrow, and low (fig. 4.26). The eyes were set back of Godzilla. toward the rear of the skull; the large nostrils were The family Stegosauridae contains about ten gen- located at the tip of the snout, opening to each side. era (Galton 1990). This family belongs to a larger A toothless beak, formed by the upper premaxillary group of ornithischians known as the Thyreophora bone and lower predentary bone, adorned the tip of or “shield bearers” in reference to the bony armor the snout. The teeth of Stegosaurus were small and of these quadrupedal herbivores (Sereno 1989). leaf-shaped, with numerous ridges and denticles Within the Thyreophora the stegosaurs are related (fig. 4.25). These teeth would probably have been to other armored ornithischians such as the ankylo- effective in shredding fibrous or tough plant tissues. saurs, a group most common in the Cretaceous, and The back of Stegosaurus was strongly arched the primitive early Jurassic forms like Scelidosau- upward, reaching a maximum height just above rus (discussed in chapter 3). The stegosaurs are the the hips (fig. 4.26). The vertebrae of the mid-back most common late Jurassic thyreophoran dinosaurs, region were tall and had upward directed transverse although in some places their remains are found in processes (fig. 4.27). The ribs attached to these pro- Cretaceous strata as well. cesses at nearly right angles to form a deep but nar- All stegosaurids have a dorsal row (or rows) of row rib cage. The neck was relatively short, and the bony armor that extended along the back, project- head was carried low to the ground. The hind limbs ing upward from the spinal column. This armor of Stegosaurus were much longer than the forelimbs may include both plates and spikes of various and were massive and pillarlike to support most of shapes, sizes, and arrangements in the many gen- the weight of the animal. Each hind foot had three era of stegosaurids. The skulls of stegosaurids are robust toes tipped with hooflike claws. The short The Late Jurassic 107

4.26. Skeleton of Stegosaurus ungulatus, based on the reconstruction of Gilmore 1914. Note the highly arched back that supports the distinctive plates. The forelimbs were much shorter than the hind limbs, giving this dinosaur a crouching posture.

some consistent similarities. The plates extend from just behind the skull and in rows to cover the entire neck, back, and about three-fourths of the tail. The neck plates are small and more or less rectangular, increasing in size along the back to the hips, where the largest of the bone plates were located. The plates of the back generally become more triangular in shape toward the hips and in some species tapered to a sharp point directed upward. The plates become smaller in the forward portion of the tail but have relatively broad bases. The spikes were restricted to the end of the tail. The number of spikes appears to have been variable in different species: at least four and perhaps as many as eight or more. The function of the plates in Stegosaurus has been the subject of considerable disagreement and 4.27. A dorsal vertebra from Stegosaurus. The high neural arches and upward flaring transverse processes are discussion among paleontologists ever since the first typical of the stegosaurs. Scale bar = 4 inches (10 cm). specimens of this genus were described in the 1890s. Redrawn from Galton 1990. The plates have been variously regarded as defensive devices (e.g., Gilmore 1914), as display structures forelimbs were constructed of stout bones with (e.g., Colbert 1961), or as providing a thermoregu- prominent ridges for the attachment of strong mus- latory mechanism (Farlow and others 1976; de Buf- cles in the upper “arms” and shoulder. The five toes frenil and others 1986). Perhaps the most revealing of the forefeet had smaller hooflike claws. clue in this puzzle is the detailed structure of the For most people, the armor plates and spikes plates. The plates have very thin walls of bone sur- along the back of Stegosaurus are its most distinc- rounding a “spongy” center that was probably full of tive feature. The size, shape, and pattern of the plates blood when the animal was alive. Moreover, the sur- appear to have varied somewhat among the sev- faces of the larger plates usually have sinuous chan- eral known species of Stegosaurus, but they all have nels, suggesting that a network of blood vessels may 108 Chapter 4 have existed on the surface of the plates. It doesn’t rows of plates. Alternately, however, we might inter- make sense that the plates would have been so thin pret the overlap of the plates as a consequence of and supplied with such copious amounts of blood the displacement of a single row of plates along if they functioned as defensive organs. The plates the back. S. A. Czerkas (1987) reviewed the vari- could have been easily damaged during an attack of ous theories of plate arrangement and concluded a large theropod. Any Stegosaurus that suffered sig- that Stegosaurus most likely possessed a single row nificant damage to its plates might easily have bled of plates. Although this concept has become pop- to death. Also, the plates were attached just beneath ular and is featured in several recent reconstruc- the skin and were anchored into the shallow mus- tions of Stegosaurus, it does contradict the primitive cles along the back. Because they were not rigidly archosaur pattern of paired rows of dermal plates connected to the bones of the back, the plates would in the skin. Crocodiles still retain this pattern. Until have been easily deflected, offering little resistance more complete and intact specimens of Stegosau- to an attacking carnivore. rus are discovered, we must at least acknowledge the It seems far more likely that the plates of Stego- possibility of a paired row of plates garnishing the saurus were used to warm or cool the body. On humped back of this ornithischian. warm days, or following periods of exertion, the As slow-moving herbivores, the stegosaurs would plates could have been positioned into the breeze. have been under constant threat of attack from the The overheated blood that flowed through the plates carnivorous theropods of Morrison time (discussed and over their surfaces could have been cooled in in the next chapter). If the plates offered little pro- this way. When its body temperature fell below the tection and flight was not possible, how did Stego- optimal range, Stegosaurus might have been able saurus defend itself? This was almost certainly the to elevate its core temperature by facing the plates function of the tail spikes. The spikes were long and toward the sun in a manner similar to the way liz- covered by a tough sheath that tapered to a sharp ards warm themselves on a cold day by basking in point. They could clearly inflict a serious wound. In the sunlight. It is also possible, of course, that the addition, the spikes were angled upward and out- plates served more than one function, but it does ward from the top of the tail, so that the thrashing not seem likely that they were used primarily for of the tail from side to side would have produced defense. We might think of the plates as primar- a dangerous situation for any animal approaching ily thermoregulatory structures that could also have from the rear. K. Carpenter and others (2005) have been used to attract mates or to communicate spe- analyzed the spike strength, tail mechanics, and evi- cies identity to other stegosaurs. dence from damaged fossils from both Stegosau- Almost as controversial as the function of the rus and the contemporaneous predator Allosaurus plates is their precise arrangement along the back to conclude that an antagonistic predator-prey rela- of Stegosaurus. This issue remains unsettled for one tionship existed between these two dinosaurs. simple reason: no Stegosaurus skeleton has ever Attacking a Stegosaurus from the rear obviously been discovered with the full set of plates in their would have been hazardous, but what about pred- original position. Because the plates were not con- ators that might have approached from the side or nected to the skeleton, they quickly became scat- front? Remember that Stegosaurus had most of its tered and repositioned when the skin and muscles weight centered over the hips and the shoulders decayed after death. In partial skeletons represent- were heavily muscled. The forelimbs of Stegosaurus ing a Stegosaurus carcass lying on its side, the pre- seem to have been well designed to deliver a pow- served plates are sometimes found overlapping one erful sideways push to the front of the body. Such another. This might suggest that there were two a rapid lateral movement of the forward portion of 4.28. Stegosaurus and Ceratosaurus. The muscular tail of Stegosaurus, studded with sharp spikes, would have been effective in deterring attacks from predators approaching this slow-moving dinosaur from the rear. Illustration by Carel Brest van Kempen. 110 Chapter 4 the body would have allowed Stegosaurus to pivot diplodocids could not process with their diminu- swiftly around the hips, redirecting its tail toward tive, weak teeth. the attacking predator. We could well envision a Another Morrison stegosaurid, Hesperosaurus Stegosaurus under attack quickly whirling around, mjosi, was described by Carpenter and others (2001) while wildly flailing its tail back and forth. The from an unusually complete skeleton discovered in image is not unlike the behavior of a porcupine that Wyoming. This animal was similar to Stegosaurus bristles its quills and slaps its tail at any threatening but had lower and more elongated plates along its animal. In defending itself, a Stegosaurus might have back and a proportionally shorter head. Otherwise behaved a bit like a multiton porcupine (fig. 4.28). Hesperosaurus was so similar to Stegosaurus that In addition to the tail spikes, many small circu- some paleontologists (Maidment and others 2008) lar plates of bone were imbedded in the skin cover- consider Hesperosaurus to be one of several different ing the neck and belly regions of Stegosaurus. These species of Stegosaurus. Many types of plated dino- small plates, known as dermal ossicles, afforded at saurs clearly were roaming through the underbrush least some protection to these otherwise vulnerable of the Morrison basin. portions of the body by making the skin less pene- trable to the teeth and claws of predators. Suborder Ankylosauria At least a half-dozen species of Stegosaurus have been described by paleontologists, but only two Stegosaurus was not the only armor-plated ornithis- seem to have been common in Utah. S. ungula- chian on the Morrison plain. Small circular to rect- tus was the larger and evidently more common of angular plates of bone with a raised keel have been the two. Its remains have been found in the Morri- found in several Morrison dinosaur localities that son Formation in Colorado, Wyoming, and Utah. might indicate the presence of primitive members S. ungulatus was generally 15–25 feet (5–8 meters) of the suborder Ankylosauria. These fragments of long, with relatively long hind limbs, a high rump, dermal armor are quite different from the plates, large dorsal plates, and as many as eight tail spikes, spikes, and ossicles associated with the remains of though some studies suggest fewer (Carpenter Stegosaurus. The ankylosaurs are best known from and Galton 2001). The smaller species of Stego- the Late Cretaceous, however, when these gigan- saurus, S. stenops, was usually less than 15 feet (5 tic and heavily armored herbivores were widely dis- meters) long, possessed relatively short limbs and tributed throughout the world. Few ankylosaurs are a lower rump, and had four tail spikes. The larg- known from the Jurassic. The origin of the anky- est individuals of S. ungulatus might have weighed losaurs remains uncertain, but the well-developed as much as 6 tons, while the smaller S. stenops nor- bony armor, quadrupedal posture, and other traits mally weighed between 1 and 2 tons. Both species suggest that they are more closely related to the Scel- were clearly low browsers and seem well adapted to idosaurus-Stegosaurus group than to other ornith- subsist on coarse and tough vegetation. As noted ischians. Recognizing the kinship between these earlier in this chapter, Stegosaurus is commonly dinosaurs with such bony coverings, the large clade associated with the diplodocid sauropods, partic- Thyreophora has been established by paleontologists ularly Apatosaurus, in many Morrison fossil quar- to include all plated, spiked, and armored ornithis- ries. Because the teeth and jaws of these two groups chian dinosaurs. Nevertheless, the skulls and skeletal of dinosaurs are so dissimilar, it is not likely that features of the ankylosaurs are much different from they competed for the same food resources. Stego- those of the stegosaurs, so the divergence between saurus, with its shredding teeth and chopping these two groups of dinosaurs must have occurred beak, probably consumed plant fodder that the early in their common evolutionary histories. The Late Jurassic 111

The nature of mysterious ankylosaurlike plates group of bipedal and semiquadrupedal herbivores found in the Morrison Formation was illuminated that exhibit many advanced specializations. The cli- by the recent discovery of the oldest ankylosaur in max of ornithopod evolution occurred during the North America in this formation. J. I. Kirkland and late Cretaceous, when they became the most suc- K. Carpenter (1994) and Kirkland and others (1998) cessful dinosaur herbivores on a global scale. The have identified the partial remains of the primitive ornithopods include the familiar “duck-billed” ankylosaur Mymoorapelta maysi from Morrison out- dinosaurs such as Edmontosaurus, Corythosaurus, crops near the Utah-Colorado border. Mymoorapelta and the crested Parasaurolophus, which all might was a small quadrupedal herbivore that had a well- serve as good examples of basic ornithopod design. developed bony plate covering the hip region and But this subclass includes many other types of her- triangular plates projecting outward on either side bivorous dinosaurs that are less specialized than the of the tail. Mymoorapelta evidently had many circu- duck-billed representatives. In the late Jurassic the lar to oval plates (scutes) imbedded in the skin else- true duck-billed dinosaurs (families Hadrosauri- where on its body. Small isolated scutes similar to dae and Lambeosauridae) had not yet evolved from those of Mymoorapelta are also known from several their more primitive ancestors. Among the subor- other localities in Utah, indicating that this anky- der Ornithopoda in the late Jurassic we find instead losaur (or a close relative) was widely distributed several different groups of a more primitive charac- across the central interior basin during late Jurassic ter, such as the iguanodontids, hypsilophodontids, time. The skull is missing in the specimen described and fabrosaurids. Such groups traditionally have by Kirkland and Carpenter (1994), and only a few been considered to represent families of ornithopod bones of the limbs were found. Though the skele- dinosaurs, but it is still somewhat uncertain which tal material from Mymoorapelta is incomplete, it primitive ornithopods belong in which families. is clear that this dinosaur is a primitive member of Several schemes of classification recently have been the suborder Ankylosauria and thus documents the proposed for these groups (e.g., Sues and Norman presence of such armored dinosaurs in the Morri- 1990; Weishampel and Heinrich 1992), but the cat- son fauna. In addition, a second large ankylosaurid egories are not always consistent. Despite the com- dinosaur named Gargoyleosaurus (“gargoyle reptile”) paratively primitive character of the late Jurassic was recently identified from Morrison sediments in ornithopods and the confusion about their classifi- Wyoming (Carpenter and others 1998; Killbourne cation, they were still highly successful during their and Carpenter 2005). While the armored ankylo- time and were an important element in the Morri- saurs were certainly not commonplace in Utah dur- son ecosystem. Let’s examine a few of the ornitho- ing Morrison time, several different kinds of these pods known from the Morrison Formation. beasts may have been roaming the Morrison basin in Utah during the late Jurassic. The Morrison anky- Family Camptosauridae and Iguanodontidae losaurs suggest that this group of dinosaurs had def- Most of the late Jurassic ornithopods known initely taken the first evolutionary steps toward the from Utah belong to two groups of relatively prim- spectacular success that awaited them in the Creta- itive members of the suborder. The iguanodontids ceous period. and camptosaurids are so similar that they have sometimes been considered members of a single family, but recent reevaluations place them in dif- Suborder Ornithopoda ferent groups within a larger clade known as Anky- The ornithopod ornithischians (see the appendix lopollexia. While the details of the early branches on dinosaur classification) are a large and diverse of the ornithopod family tree are still uncertain 112 Chapter 4 and somewhat controversial, we will discuss the iguanodontids and camptosaurs together for the sake of simplicity. The iguanodontids were all relatively large, heavily built, and mostly bipedal herbivores. The camptosaurids were generally smaller and less specialized, with fewer adaptations for quadrupedal posture. Their skulls of both were long and only moderately deep, with relatively 4.29. Skull of Camptosaurus. Total length is approxi- simple teeth and a beaklike snout. An elongated mately 14 inches. recess on either side of the skull formed a “cheek pocket,” a feature that would become even more Camptosaurus thoroughly chewed its food with its prominent in the later hadrosaurs and lambeo- small, leaf-shaped teeth. saurs. The limbs were stout and massive, and the The hind limbs of Camptosaurus were power- toes were tipped with hooflike structures. The hind ful and no doubt supported most of the animal’s limbs were clearly larger than the forelimbs, but the weight and provided the main propulsion for the iguanodontids could probably support their bod- body (fig. 4.30). The four large toes of the hind foot ies in either a bipedal or quadrupedal posture. The were equipped with hooflike claws. The forelimbs iguanodontids and camptosaurs both have a thumb were smaller than the hind limbs but were still rela- on the manus (hand) that was shaped like a spike tively stout. The thumb spike of Camptosaurus was and projected inward from the other four digits. comparatively small, and the other four digits of the This unique conical thumb spike is one of the most manus had small, pointed, hooflike claws. These fea- distinguishing characteristics of the iguanodontids tures, coupled with the solid construction of the and is also present in the camptosaurs, though only wrist, suggest that Camptosaurus frequently sup- weakly developed. ported itself in a quadrupedal fashion even though Camptosaurus it was fully capable of a bipedal stance. The beak and Camptosaurus is the most common of the Morri- teeth indicate that Camptosaurus was probably a son ornithopods and the only member of the prim- low-browsing herbivore, so it is reasonable to envi- itive groups that can be regarded as abundant and sion it feeding in a quadrupedal posture, while it widespread. The remains of Camptosaurus have used the hind limbs alone while walking or running been found in many sites across Utah, Colorado, from place to place. and Wyoming, including both the Cleveland-Lloyd Camptosaurus teeth are relatively small, but they Quarry and Dinosaur National Monument. Com- appear to be well designed for shredding leafy veg- pared to the iguanodontids, Camptosaurus was of etation. Its short neck and modest body size pre- modest size: most specimens are about 15–18 feet vented Camptosaurus from reaching high-growing (5–6 meters) long and weigh between 1,500 and vegetation. The neck was rather flexible, though; 2,200 pounds. Unusually large Camptosaurus fossils coupled with the quadrupedal feeding stance, this are occasionally found, suggesting that the biggest probably made Camptosaurus very efficient as a for- individuals might have grown to 28 feet (9 meters) ager among the low-growing late Jurassic shrubs. in length and attained a body weight closer to 3 or 4 It probably fed at about the same level as Stegosau- tons. The skull of Camptosaurus was long and low, rus but may have selected the more tender plant with a toothless beaklike tip formed from the pre- tissues as its primary food. Unlike Stegosaurus, how- maxilla and predentary bones (fig. 4.29). The well- ever, Camptosaurus does not appear to have pos- developed cheek pockets in the skull suggest that sessed any defensive armor to protect itself from the The Late Jurassic 113

4.30. Skeleton of Camptosaurus dispar based on the drawing by Robert Bakker from Norman and Weisham- pel 1990. This reconstruction shows Camptosaurus in a bipedal running stance. It was also capable of supporting the body in a quadrupedal posture. This species of Camptosaurus was about 15 feet long and stood about 4 feet high at the back.

fearsome predators of the Jurassic. The thumb spike, behavior that enabled Camptosaurus bands to detect which might have been used as a defense weapon the approach of predators and to confuse them when in the iguanodontids, is so small and weakly devel- they attacked. Many of the herding animals in mod- oped in Camptosaurus that it probably could not ern grassland and forested habitats employ this have inflicted a very serious wound on an attack- mechanism of survival. It rarely prevents the loss of ing theropod. Furthermore, though it could move animals from the herd but certainly limits the suc- efficiently in a bipedal stance, Camptosaurus was cess of the predators to a tolerable level that enables not particularly well designed for speed. Many late the herd as a whole to survive. In the absence of Jurassic theropods could probably have outrun it, at armor or any extreme specializations for speed, it least for short distances. is likely that Camptosaurus depended primarily on We might wonder how Camptosaurus, without camouflage or group behavior or both to survive the protective armor and with limited abilities for flight, relentless attacks of dinosaur predators. managed to survive the attacks of carnivores. At least Several different species of Camptosaurus have two possibilities seem plausible. First, Camptosau- been identified from the Morrison Formation. The rus probably spent a great deal of time feeding in the recent compilation of D. J. Chure and others (2006) dense foliage of more forested areas within the Mor- lists two species as valid among many other obso- rison basin. In this shadowy environment protective lete or dubious taxa: C. dispar, the most widespread coloration may have helped conceal individuals from form, and the less common C. amplus. In addition, predators. Such natural camouflage is employed by Carpenter and others (2008) identified a third spe- many browsing mammals in the modern world and cies, C. aphanoecetes, from Dinosaur National Mon- would have been particularly valuable to Camp- ument on the basis of differences in the shape and tosaurus when it was feeding in a head-down pos- proportions of the bones of the limb and spine. It ture. Skin does not readily fossilize, so the coloration has already been suggested (McDonald 2011) that and patterning of the integument of Camptosau- this third species may belong to a separate genus, rus remain unknown. It is at least possible, though, Uteodon. The proliferation of names describing the that this ornithopod had mottled patches or bars variations in Camptosaurus fossils implies the exis- of color that would have made it less visible in the tence of several species of similar animals in the late Jurassic shrubbery. Another effective means of Morrison basin in Utah; but without more complete defense might have been herding or other group fossils we can’t be sure about exactly how many. 114 Chapter 4

Iguanodon(?) Iguanodon was similar in basic overall design Iguanodon was one of the first dinosaurs ever to Camptosaurus but was substantially larger. An discovered. Gideon Mantell applied this name to adult Iguanodon attained a body length up to 35 some fragmentary fossils found in England in 1825. feet (12 meters), nearly twice as long as an average The name, meaning “iguana-tooth,” was inspired by Camptosaurus. Iguanodon also seems to be more the leaflike teeth of Iguanodon, which bear a strong advanced than Camptosaurus in that it had a much resemblance to those of the modern iguana in that more prominent thumb spike, one less toe (three) they have long ridges leading to small denticles on each hind foot, and an intricate system of criss- along the cutting edge. The teeth are not dissimilar crossing tendons that helped to strengthen the back to those of Camptosaurus, and other skeletal simi- and tail. The skull of Iguanodon was deeper and lon- larities unite Iguanodon and Camptosaurus within ger than that of Camptosaurus and contained more the family Iguanodontidae. Iguanodon was thought and larger teeth. The forelimbs of Iguanodon are be a strictly European dinosaur for many years after proportionally larger than those of Camptosaurus, its discovery. Recently, though, its remains were and the forefeet are more robust. These features sug- reported from the Morrison Formation of west- gest that Iguanodon may have assumed a quadrupe- ern Colorado (Armstrong and others 1987). This dal posture more frequently than did Camptosaurus. was a surprising discovery because it suggested that Iguanodon lived in North American in the late Family Hypsilophodontidae Jurassic, millions of years earlier than the European The hypsilophodontid ornithischians were Iguanodon, which occurs in early Cretaceous depos- mostly small (roughly 6–15 feet [2–5 meters] long), its. Perhaps the Morrison specimen was the world’s bipedal herbivores that were most common in the oldest Iguanodon. late Jurassic and early Cretaceous. Most hypsiloph- The Morrison fossils were very scrappy, consist- odontids were lightly built creatures with slender, ing of a portion of the jaw and a few loose teeth. long hind limbs that are well-designed for running. Iguanodon was so similar to Camptosaurus that it The forelimbs are smaller than the hind limbs and is not easy to distinguish between the two ornitho- have five-finger hands that lack the hooflike claws of pods with such limited fossil material. Though addi- the iguanodontids. The tails of hypsilophodontids tional supposedly Iguanodon material was later were generally braced by a basketlike network of recovered from the site, it was not sufficient to prove tendons that would have made them quite rigid in that the specimen was not Camptosaurus. Many life. The beamlike tail was probably used as a coun- paleontologists are still not sure whether the west- terbalancing stabilizer that would have enhanced ern Colorado fossils really do represent Iguanodon. the maneuverability of the hypsilophodontids as Though no Iguanodon fossils have yet been posi- they ran. The skulls of hypsilophodontids are small, tively identified in Utah, its possible occurrence in with a narrow horny beak at the tip. The small teeth western Colorado suggests that it could have lived are somewhat variable in form, from leaf-shaped in Utah as well during the late Jurassic. Because to triangular to chisel-like in the dozen or so dif- Iguanodon is known from later Cretaceous strata in ferent genera of hypsilophodontids. But the bones Utah, let’s briefly examine the differences between of the snout are weakly joined in such a way that Iguanodon and Camptosaurus to learn how the two the maxilla (upper “cheek” bone) could pivot out- dinosaurs differed from each other. Perhaps some- ward past the lower jaw while a hypsilophodontid day new fossil discoveries will allow us the settle the chewed its food. This transverse movement between “Morrison Iguanodon” issue once and for all. the upper and lower teeth probably allowed the The Late Jurassic 115 hypsilophodontids to process their plant food into a easily digested pulp. Dryosaurus Dryosaurus is by far the most common and well- known member of the hypsilophodontid group from the Morrison Formation in Utah and adjacent regions of western North America (Shepherd and others 1977; Galton 1981, 1983). Several skeletal features of Dryosaurus are different from the general hypsilophodontid pattern (see the discussion below), however, leading to confusion about its family-level classification. Some paleontologists consider Dryosaurus to be an advanced member of the family Hypsilophodontidae (Galton 1983), while others place it in a separate category known variously as the Dryosauridae (Sues and Norman 1990) or the Dryomorpha (Sereno 1986). Still other paleontologists have suggested that Dryosaurus is an iguanodontian, closely related to Camptosaurus 4.31. Skulls of an adult (top) and a baby (bottom) Dry- (Weishampel and Heinrich 1992). osaurus. The adult skull is about 8 inches long, while However we classify Dryosaurus, it is a very the baby skull is about half that size. The eyes were relatively larger and the face relatively shorter in the baby interesting element of the Morrison dinosaur fauna. skull. Sketch of the baby skull after Carpenter 1994. Originally named Laosaurus altus by O. C. Marsh in 1878, Dryosaurus was a relatively small bipedal herbivore, ranging in length from about 6 feet to 10 feet (2–3.3) or more. An adult Dryosaurus would have weighed about 200 pounds and stood some 3–4 feet (1 meter) tall at the hip. The skull of Dryosaurus was small and delicate, similar to those of the hypsilophodontids (fig. 4.31). Unlike the true hypsilophodontids, however, Dryosaurus had no teeth on the bone (the predentary) that forms the lower tip of the snout. The leaf-shearing teeth of Dryosaurus are small, with prominent ridges on the flat surfaces and small denticles along the edges (fig. 4.32). These 4.32. Typical upper teeth of Dryosaurus (right) and of teeth are more elongated and triangular in shape Hypsilophodon (left). The teeth of Dryosaurus are longer and have a prominent ridge on one side, one of several than those typical of the “true” hypsilophodontids. differences between it and the true hypsilophodontid Wear surfaces on the teeth of Dryosaurus indicate dinosaurs. The teeth are only about 0.2 inch long. that it chewed its food thoroughly, using the flexible Redrawn from Sues and Norman 1990. upper jaws to move the upper and lower teeth past each other in a manner similar to that of the more was relatively blunt, suggesting that it might have typical hypsilophodontids. The snout of Dryosaurus browsed close to the ground. 116 Chapter 4

4.33. Skeleton of Dryosaurus altus. Dryosaurus was probably a speedy runner, a behavior suggested by the large hind limbs and rigidly braced back. Drawing based on reconstruction of Gregory S. Paul in Sues and Nor- man 1990.

Dryosaurus was evidently a speedy little dino- Dryosaurus looked like. The tiny baby skulls had saur. It had long and well-muscled hind limbs (fig. large eyes compared to the adult and a less elon- 4.33). The hind feet had only three functional toes gated snout (fig. 4.31). These distinctions between rather than four, which is the case in most other adult and baby dryosaurs are similar to those in hypsilophodontids. Because it results in a decrease many other animals, particularly the birds, in which in the frictional contact between the foot and the the young appear to have large eyes and short faces. ground, the reduction of toes is usually interpreted As they matured, the baby dryosaurs probably fol- as an adaptation for swift running. Furthermore, the lowed the same pattern that we see in modern birds vertebrae in the middle of the back of Dryosaurus, and mammals: the head grows faster than the eyes, from the hips to the shoulders, were braced by bony while the adult snouts develop from the lengthen- tendons that would have strengthened the spine. ing of the skull. In this way the babies gradually lose This feature, also seen in other bipedal dinosaur their infantile proportions. Depending on its age, a herbivores, would have helped transfer the force of baby Dryosaurus was probably not much larger than the hind limbs to the body, an additional specializa- a modern robin and would easily have fit into the tion for speed. palm of your hand. Perhaps the most intriguing aspect of Dryosau- Even though paleontologists have discovered fos- rus is the frequency with which fossils representing sils of the babies of several different dinosaurs in small babies of this genus have been found. At least recent years, such fossils remain relatively rare. The 2,500 bone fragments have been found associated frequency of juvenile Dryosaurus remains in the with eggshell fragments at a site in western Colo- Morrison Formation of Utah and nearby regions is rado. About 90 percent of these small bones repre- unusual. Perhaps the conditions on the broad allu- sent baby dryosaurs, ranging in size from embryos vial plain were well suited to those required by to immature adults (Scheetz 1991). It seems likely, Dryosaurus for successful mating and nesting. An though not certain, that many of the eggshell frag- embryo of Camptosaurus was also recently discov- ments from this locality represent the remains of ered at Dinosaur National Monument (Chure and Dryosaurus eggs from a nest. In addition, at Dino- others 1994). It thus appears that at least two types saur National Monument, where some of the best of ornithopod dinosaurs found favorable breed- Dryosaurus fossils in the world have been recov- ing and nesting conditions on the lowland plains of ered, a 4-inch-long (10-centimeter) baby dryosaur Utah during the late Jurassic (fig. 4.34). It seems that skull was discovered in 1922 and recently recon- the other larger dinosaurs preferred to nest else- structed by Carpenter (1994). From these discov- where for some reason, because embryos and juve- eries we have a reasonably good idea what a baby niles of other genera are much less common in the The Late Jurassic 117

4.34. A Dryosaurus nest in the Morrison interior basin. Illustration by Carel Brest van Kempen. 118 Chapter 4 floodplain and river-deposited sediments of the In life Othnielia probably weighed no more than Morrison Formation in eastern Utah and western about 30 pounds as a full-grown adult and would Colorado. Maybe the relative abundance of ornitho- have been even smaller as a juvenile. It had primi- pod babies in this region is just the result of chance tive, leaf-shaped teeth and evidently lacked the well- discoveries. Or perhaps it was the combination of developed cheek pouches that were common in the factors such as the abundance of food, the ability to more advanced ornithopods. It seems that both Oth- conceal the nest, the ease of finding mates, and the nielia and Othnielosaurus favored the sheltered envi- favorable climate that created near-optimal condi- ronments (Russell 1989), where they coexisted with tions for the ornithopods to procreate on the Mor- each other and a variety of other small creatures. rison plain. One thing is certain: the breezes that drifted across the late Jurassic landscapes of eastern Other Ornithopods and Small Animals Utah would commonly have carried the chirps and of the Morrison squeals of baby dinosaurs. Othnielia and Othnielosaurus In addition to the ornithopod dinosaurs already Othnielia, named for the illustrious American described, the Morrison fossil record indicates that paleontologist Othniel C. Marsh (Galton 1977), is other members of this group may have lived in Utah a poorly known bipedal herbivore that seems to during late Jurassic time. Nanosaurus was a tiny be a member of the family Hypsilophodontidae. ornithopod dinosaur about 2 feet (0.6 meter) long Our knowledge of the skeletal anatomy of Othn- that weighed perhaps 2 pounds. This bird-sized her- ielia is limited by both its rarity and the fragmentary bivore is known from fragmentary remains exca- nature of the few partial skeletons that have been vated from late Jurassic strata in Colorado but has discovered. yet to be identified with certainty from Utah expo- This dinosaur has been known by several other sures of the Morrison Formation. What we know of names, including Nanosaurus rex and Laosaurus the overall skeletal architecture of Nanosaurus sug- gracilis. Another very similar dinosaur was orig- gests a very primitive ornithischian, but our knowl- inally known as Laosaurus consors, a species that edge of its anatomy is so poor that paleontologists paleontologist Peter Galton renamed Othnielosaurus do not agree as to which family it should be placed consors (Galton 2007). While Othniella and Othn- in. Some paleontologists regard Nanosaurus and ielosaurus are currently regarded as valid and sep- Othnielia as small and large variants of the same arate genera, they are very similar to each other in species, while others question the validity of Nano- their overall features and are closely related, so I will saurus as a genus and still others (Galton 2007) describe them together as a pair of sister genera. place it into a very primitive basal lineage such as Paleontologists have some lingering disagreement the unspecialized heterodonosaurids. about the family-level classification of Othnielia and Drinker nisti was identified in 1990 from small Othnielosaurus, which is not surprising given the bones collected from the Morrison Formation in limited information we have concerning their skel- Wyoming (Bakker and others 1990). This was a very etal characteristics. I will describe these dinosaurs small hypsilophodontid some 6 feet (2 meters) in as hypsilophodontids, because they both seem most length that weighed about 20–25 pounds. On the similar to that group of dinosaurs. basis of its simple and unspecialized teeth, it appears The scrappy remains of Othnielia/Othnielosaurus to have been a very primitive member of the hypsi- known to date suggest that the skeleton was similar lophodontid group. to but substantially smaller than Dryosaurus, with a Although Nanosaurus and Drinker are both length not exceeding about 7 feet (about 2 meters). poorly known and not yet documented from Utah The Late Jurassic 119 exposures, they serve as a reminder of an important primitive mammals, pterosaurs, turtles, crocodiles, fact about the Morrison ecosystem. Even though we and snakes lived with the dinosaurs in the Morri- refer to the late Jurassic as the Golden Age of Sauro- son basin. A thorough review of all these nondino- pods, many smaller creatures played equally impor- saur animals is beyond the scope of our exploration tant roles in the ecological drama that continued in of Utah dinosaurs, but we should not overlook their eastern Utah for some 10 million years in the late importance as vital elements in the ecological sys- Jurassic. We know little about the small creatures tem that supported the larger dinosaurs. that populated the Morrison plain in comparison Up to this point I have not specifically men- to our knowledge of the sauropods, but that does tioned the animals that were positioned at the top not mean that these small creatures were unimport- of the Morrison food chain: the theropods. All the ant or uncommon. Instead this situation is probably herbivorous dinosaurs, along with the smaller non- a reflection of the historical bias toward the col- dinosaur vertebrates, represented an enormous lecting of large fossils (discussed in chapter 1). We food base for creatures designed to consume flesh. are gradually learning more about the many kinds Responding to the virtually unlimited opportunities of small animals (dinosaurs and nondinosaurs) for predation, the theropods of the Morrison repre- that were important elements of the overall Morri- sent a fascinating assemblage of fearsome creatures son fauna. Some of the recent work (e.g. Callison cloaked in tooth and claw. They will be the focus of 1987; Gorman and others 2008; Foster 2009) dem- our next peek into the late Jurassic world of Utah. onstrates that a rich fauna of insects, fish, lizards, Chapter 5 Blood Brothers 05The Predators of the Morrison Formation The theropod dinosaurs represent to many people amount of variation on the general themes of flesh- the quintessential prehistoric monsters. The per- eating and bipedal movement. ception of them as colossal eating machines with a Consequently the theropods represent a highly fierce demeanor and savage nature has been fostered differentiated group of dinosaur predators. Their by countless portrayals in movies and books that individual specializations for greater meat-eating project such a ferocious image. From Arthur Conan efficiency are amazingly varied. So numerous are Doyle’s Lost World, published in 1914, to the Jurassic the variations on the general theme of bipedal car- Park books and The Lost World by Michael Crich- nivory among the theropods that their classification ton, we seem to love our fear of theropods. They are has been a subject of constant debate among paleon- everybody’s favorite dinosaur villains. tologists. A confusing snarl of taxonomic categories In reality the theropods were fascinating crea- for the theropod dinosaurs has become established tures that exhibit many remarkable adaptations over the past century, reflecting the complexities for survival and success as predators in the Meso- and variations in their form. zoic world. As a group, the suborder Theropoda is The suborder Theropoda was established in enchanting for reasons other than the sense of ter- 1881 by O. C. Marsh to encompass all the carnivo- ror evoked by their perceived ferocity. They are rous dinosaurs known at that time (only a few, of wondrous examples of the efficiency of natural course). As more and more fossils of carnivorous selection in driving the process of adaptation and dinosaurs were discovered, it became necessary to change in living systems. In many ways the thero- subdivide the Theropoda into smaller groups. The pods represent a conservative lineage of dinosaurs, earliest subdivision was more based on size than on because they all consistently retained the bipedal any other feature. Thus Coelurosauria was estab- stance and carnivorous habits of the earliest dino- lished as an infraorder to accommodate the smaller saurs and dinosaur ancestors. Other groups of dino- carnivores, while the larger forms were placed into saurs, such as the sauropods and ornithischians, the infraorder Carnosauria. Several new orders radically modified these original characteristics as and other taxonomic groups were added later as they became specialized for the variety of herbivo- the diversity of the theropods steadily increased rous roles that they played in the Mesozoic ecosys- due to continued research and collecting. Various tem. But not the theropods. Throughout the entire infraorders, families, and subfamilies were estab- era of dinosaur dominance, they never abandoned lished as the need arose. Soon the classification of the basic traits of the earliest members of the Dino- the theropods was a confusing weave of taxonomic sauria. If we closely examine the details of theropod threads that often obscured the true relationships design from the earliest and most primitive carni- among the various groups. vores (such as Herrerasaurus) to the most advanced The basis of the modern taxonomy of the the- forms (such as Tyrannosaurus and other Creta- ropod dinosaurs was established when J. Gauth- ceous predators), however, we observe an amazing ier revised the classification of the entire suborder

120 Blood Brothers 121

(Gauthier 1986; Rowe and Gauthier 1990). In this the fact that the categories they produce are less modern classification most of the theropods con- subject to individual judgment and make a much stitute a clade known as the Tetanurae, which stronger statement about ancestry and evolution includes modern and prehistoric birds. Another than did the orthodox taxonomy of the past. Gradu- group of more primitive carnivorous dinosaurs ally, as the modern cladistic classification of the the- has been referred to as the Ceratosauria. The rela- ropods (and other dinosaur groups, too) is refined, tionships between these two broad clades are still some of the confusion created by unnatural assem- being debated, with several proposed subdivisions blages such as the “coelurosaurs” and “carnosaurs” is of each clade (see the review of Carrano and Samp- beginning to clear. son 2008). The Tetanurae and the Ceratosauria The Ceratosauria and the Tetanurae represent are separated from each other on the basis of sets groups of dinosaurs that share a common evolution- of characteristics that are considered to be either ary history. Together they represent the theropod primitive or advanced. The set of primitive features clade of saurischian dinosaurs. Thus the Tetanurae is the basic blueprint for the entire theropod clan, and Ceratosauria technically are not infraorders while the more advanced (or “derived”) groups are or families because they are not established on the distinguished by evolutionary innovations that are basis of overall morphological similarity but instead superimposed upon the older, primitive frame- reflect the primitive characteristics of some thero- work. This approach to classification, based on the pods and the specialized (or “derived”) nature of distribution of primitive and derived character- others. Ceratosauria is the more primitive clade and istics, is known as cladistics and has become the consists of only about ten different genera, while the dominant method of subdividing the various dino- more specialized Tetanurae clade represents a larger saur taxa. set of derived and highly varied theropods, among Earlier schemes of theropod classification that which at least sixty-five genera are recognized. stressed overall morphological similarity have become less popular because they often resulted in Theropods of the Morrison Formation the grouping together of creatures that were probably not closely related in an evolutionary sense. The At least ten different theropods have been identi- category “coelurosaurs,” for example, includes many fied from the Morrison Formation in western North different small theropods that are not actually very America. Eight of these are known from Utah sites. similar or closely related to one another, except in The Morrison theropods are a diverse array of pred- terms of size. The cladistic approach has allowed the ators ranging from gigantic beasts such as Torvosau- development of a system of classification that more rus to the unpretentious Ornitholestes, which looked accurately represents the true evolutionary relation- a bit like an overgrown bipedal lizard about 3 feet (1 ships among the various groups of theropods by meter) long. The variety observed among the the- attempting to deemphasize superficial similarities ropods identified in the Morrison Formation sug- such as size. While cladistic classifications are now gests some degree of specialization among them for used for all groups of dinosaurs, their use in thero- specific prey animals, different hunting strategies, pod classification has been well accepted for at least and variable habitats. Each of the Morrison thero- two decades. It is beyond my purpose to explore pods went about its carnivorous ways in its own dis- the contrasts between the traditional morpholog- tinctive style. The food base of prey animals was ical and the modern cladistic classifications in full evidently large enough to accommodate several dif- here, but the almost universal acceptance of cladis- ferent approaches to carnivory. We will explore tic techniques among paleontologists stems from the Morrison theropods following the current 122 Chapter 5 dichotomy of the group into the primitive ceratosaurs and the more advanced tetanurines.

Ceratosauria

The primitive Ceratosauria are defined by several characteristics that serve to separate the group from the more advanced tetanurine theropods. The skulls of the ceratosaurs are relatively heavy and long, with teeth that extend backward to at least the position of the eye socket or orbit (fig. 5.1). As in almost all theropods, the individual teeth of ceratosaurs are curved toward the rear, are flattened to a bladelike form, and have small serrations along the cutting edges, much like a steak knife. The skull is commonly ornamented by bony crests, ridges, or blade- shaped horns that are developed to varying degrees in individual specimens. The vertebrae of the backs of ceratosaurs had distinctive triangular transverse processes that 5.1. Skull of Ceratosaurus nasicornis in side (top) and top (bottom) views. Note the bladelike horn on the projected outward and back from the vertical neu- snout and the prominent brow ridges. Based on speci- ral spines (fig. 5.2B). The cervical vertebrae were men illustrated by Gilmore 1920. robust and had two pockets (pleurocoels) to conserve weight. The necks of ceratosaurs appear to ornamentation on individual skulls and the propor- have been thick, muscular, and flexible. Elsewhere tions of both the limb bones and the vertebrae of in the skeleton the ceratosaurs exhibit numerous the back. The relatively small, slender, and less bulky fusions of individual bones in the ankles, feet, and bones of the “gracile” form may signify sexual dif- pelvis (fig. 5.2A). These fusions are thought to repre- ferences, presumably the female ceratosaurs. The sent an adaptation for running, because they would larger, heavier, and more prominently ornamented have resulted in stronger limb bones and a more bones observed in the more robust variant might rigid bracing of the hind limbs by the pelvis. The represent the males. Or perhaps we have it back- pubis, which projects forward and down from the ward: the females might have been the larger form. center of the pelvis, tapers to a blunt tip in the cer- In any case the dimorphism commonly seen in ceratosaurs and lacks the expanded “boot” seen in the atosaurs does not seem to reflect the age of the ani- tetanurine theropods. The pubis of ceratosaurs is mals, because the robust and gracile forms can be also distinctive in that the platelike portion of it in recognized in bones of varying size. Sexual dimor- front of the hip socket has a small circular opening phism is the most logical interpretation of the vari- or embayment that is not observed in the Tetanurae. ation in the fossils of ceratosaurs. If the ceratosaurs One of the most intriguing aspects of the cera- were sexually dimorphic, then certain behavioral tosaurs is the common observation that the skulls attributes can reasonably be postulated. The males and other skeletal elements of the individual spe- may have used their horns and crests to compete cies seem to have had two forms. This dimorphism with each other for mates. It is also likely that the is usually expressed by distinct differences in the ceratosaurs had a “breeding season,” during which Blood Brothers 123

predators on a global scale. Such late Triassic and early Jurassic predators as Coelophysis and Dilo- phosaurus (discussed in earlier chapters) represent fairly specialized members of this clade that lived during the climax of ceratosaur history. It is not surprising, then, that only one of the Morrison theropods belongs to this group. Ceratosaurus, the namesake genus of the entire clade, is the last of the ceratosaurs. Despite its relatively young age, Cerato- saurus, paradoxically, seems to be the most primitive member of the Ceratosauria. Ceratosaurus nasicornis Ceratosaurus is not particularly common in the Morrison Formation of Utah, but enough of its remains have been discovered to indicate that it prowled the interior basin along with several other more advanced theropods. Ceratosaurus is the largest of the Ceratosauria, reaching an adult length in excess of 20 feet (about 7 meters). Such a full-grown Ceratosaurus would have weighed approximately a ton and might have stood about 7 feet (about 2 meters) tall at the hip. The skull of Ceratosaurus was large, lightly constructed, and relatively narrow (fig. 5.1). The upper and lower jaws had about sixty teeth. The teeth of theropods were continuously shed (or broken?) 5.2. Ceratosaurus: A. fused foot bones (metatarsals); and replaced, so some of these teeth were large and B. dorsal vertebrae in ventral view. Note the winglike processes that are strongly deflected toward the rear. some were small, depending on the time of replace- Adapted from Gilmore 1920. ment for each individual tooth. The teeth are of typical theropod form, curving slightly toward the rear, individuals would gather to acquire mates, lay eggs, with fine serrations along the cutting edges. The slic- and perhaps nurture the hatchlings. The males may ing teeth of Ceratosaurus are exceptionally long, have blossomed into vivid colors, as many modern however, and would have been extremely effective lizards and birds do, during the breeding season. in piercing the skin or ripping the flesh of prey ani- It is fascinating to envision what a male ceratosaur mals. The bone that forms the tip of the snout (the might have looked like as it was flushed with color premaxilla) held three robust teeth that were some- while strutting around the breeding grounds, flash- what less bladelike in shape than those that lined the ing its prominent crest as a display organ to attract jaws farther back. The tooth row did not extend back females or subdue rivals. beyond the orbit (or eye socket) in Ceratosaurus. The ceratosaurs were mainly a late Triassic and Perhaps the most distinctive feature of the Cer- early Jurassic group of theropods. By the late Juras- atosaurus skull is a prominent bladelike horn that sic, and throughout the ensuing Cretaceous, the tet- decorated the snout just above and behind the nos- anurine theropods were the dominant dinosaur trils. The preserved portion of this horn, likely 124 Chapter 5

5.3. Skeleton of Ceratosaurus. This theropod had a broad, flattened tail and small knobs of bone (epaxial osteoderms) along its back. Average adult length was 15–20 feet. Based on reconstruction by Czerkas and Czerkas 1991 (in chapter 3 references). covered by a tough sheath of proteinaceous material and rigidity (fig. 5.2A), while the three bones of in life, represents the minimum actual dimensions the pelvis were also fused into a solid mass. Such of the horn. The species name nasicornis, meaning fusions are not uncommon in the Ceratosauria as a “nasal horn,” is a literal allusion to what must have group and probably allowed for the strengthening been a conspicuous bony adornment. The function of those portions of the skeleton that received the of this nose horn was probably as a display organ great stresses developed during running. The neural that signaled the sex of the animal, species identity, spines and chevron bones associated with the caudal or both during times of mating. In addition to the vertebrae of Ceratosaurus were relatively long. This nose horn, the skull has other protrusions of bone. suggests that its tail was deeper and more flattened Just above and in front of the eyes, a pronounced from side to side than were those of most other the- ridge on the upper end of the lachrymal bone pro- ropods. A deeper and more massive tail would have duced an obtrusive “brow” over the eyes. This brow increased both the stability and the maneuverabil- ridge may have been covered by unpreserved horny ity of Ceratosaurus while it was running. The small material and, if so, would have been even more forelimbs ended in hands that had four functional noticeable in life than it is in the fossil skulls. The digits or “fingers,” but it is unlikely that the slender nose horn and brow ridges are among those fea- limbs could have developed a very powerful grip. tures of Ceratosaurus that are subject to the sexual Ceratosaurus evidently possessed a series of small dimorphism exhibited by all ceratosaurs. Skulls with bones in the skin, aligned in a row along the neck, especially prominent horns and crests probably rep- back, and tail. These bones, referred to as epax- resent the males, which might have used them in ial osteoderms, would have created a knobby ridge mating displays, to signify species membership or along the back of Ceratosaurus, a unique feature dominance within a group. The neck of Ceratosau- with respect to other late Jurassic theropods. rus was relatively short but thick and muscular. The Ceratosaurus remains are not particularly abun- powerful neck may have been useful in feeding, in dant in the Morrison Formation of western North the competition for mates, and for displays of the America, but this dinosaur does seem to have been cranial ornamentation. relatively widespread. Bones representing Cerato- The skeleton of Ceratosaurus was well designed saurus are known from several different Morrison for the speed that it needed to capture prey. The Formation quarries in Utah and Colorado. Cera- hind limbs were long, massive, and probably heav- tosaurus may have eventually reached other conti- ily clad in muscle (fig. 5.3). The bones of the middle nents as well. The Tendaguru Formation of Tanzania hind feet (metatarsals) were fused for extra strength has produced the remains of a ceratosaur that is Blood Brothers 125 remarkably similar to Utah’s Ceratosaurus. Migra- tetranurine theropods usually (but not always) have tion between North America and east Africa dur- fewer teeth in the jaws (all positioned in front of the ing the late Jurassic was evidently unobstructed for orbit) than in the ceratosaurs. The overall flexibility several different Morrison dinosaurs. The broad dis- and delicacy of the skull and the reduction and relo- persal of Ceratosaurus would likely have led to the cation of teeth are two of the features that suggest a development of different species in different regions. close relationship between the tetanurine theropods J. H. Madsen and S. P. Welles (2000) consider three and the birds. Ceratosaurus species valid: C. nasicornis, C. magni- The hind limbs of the Tetanurae are large and cornis, and C. dentisulcatus. These three species dif- powerful, as in the Ceratosauria, but the bones of fer from each other in the size and proportions of the pelvis, ankles, and feet are not so firmly fused various skull and skeletal features but probably rep- together. The proportions of the femur (thigh bone), resent adaptive variations within local populations tibia, and fibula (“shin” bones) and the foot bones of these theropods. are more birdlike than in the ceratosaurs. In addition, the muscle attachment scars preserved on the pelvic and hind-limb bones of the Tetanurae indi- Tetanurae cate that muscles were concentrated higher in the All Morrison theropods other than Ceratosau- hip region. This redistribution of muscle mass rus belong to the Tetanurae, the group that repre- would have increased the leverage between the vari- sents advanced or “derived” carnivores. Tetanurae ous muscles and the limb bones they operated, con- is a much larger clade than Ceratosauria and has siderably enhancing the running abilities of the been subdivided into many smaller groups. In gen- tetanurine theropods. The relatively long foot would eral the Tetanurae all possess unique specializations have given them a longer stride and a more pow- that reflect biological innovations superimposed on erful “spring” when bounding forward. The lower the set of basic characteristics that define the more (distal) end of the pubic bone in the Tetanurae was primitive Ceratosauria. expanded into a prominent bulb, known as the Overall the Tetanurae are more birdlike than “boot” or “foot.” This expansion of the pubis was are the Ceratosauria. In fact most paleontolo- probably for the insertion of abdominal muscles gists place the birds, traditionally classified as the that would help stabilize the spine as it flexed up class Aves, within the tetanurine clade. Though it and down during locomotion. This up-and-down seems to most people that birds and theropod dino- bending of the spine is also seen in many of the saurs are quite different creatures, the construc- most adept mammal runners in today’s world. Fleet tion of the hind limbs and skulls actually shows a mammals such as cheetahs, antelopes, and jackrab- great deal of similarity. The skulls of tetanurine the- bits bend the spine while they run to gain extra dis- ropods are more lightly built than those of the cer- tance and power with each stride. The tetanurine atosaurs, composed of individual bones that are theropods probably flexed their backs in much the relatively slender and less massive. In addition, the same way as they raced after prey animals. The fore- skulls of tetanurine theropods have more open- limbs of the Tetanurae are generally smaller and/or ings than those of ceratosaurs, reducing the weight more slender than those of the Ceratosauria, with of the head even more. In the Tetanurae the sixty- hands that have fewer digits (usually two or three) odd bones that make up the skull are generally more than the four-fingered hands of Ceratosaurus. loosely connected than related bones are in the cer- The origin of the Tetanurae has been an endur- atosaurs, giving the skulls a high degree of flexibility ing mystery. We assume that they must have that facilitated chewing and swallowing food. The evolved from a more primitive ceratosaur ancestor 126 Chapter 5

Carnosaurs of the Morrison Formation in Utah in (perhaps?) the late Triassic, but they seem to explode on the scene in the late Jurassic, by which All of the larger tetanurine theropods of the Mor- time several different types are already present. rison Formation, and some of the smaller ones, are The diversity of late Jurassic tetanurines suggests placed within the Carnosauria. At least two families a lengthy period of earlier evolution, but such a of carnosaurs are known from this formation: the group of derived theropods is virtually unknown Allosauridae and the Megalosauridae. Fragmentary from older strata. Many more theropod fossils fossils indicate that other groups, such as the family from the early Jurassic and late Triassic are needed Tyrannosauridae, may also have been present. The before we can begin to understand the origins of carnosaurs are characterized by relatively massive the Tetanurae. In any event the tetanurine thero- skeletons, constructed of bones that were robust and pods were clearly the dominant meat-eaters of the heavy in comparison to those of the coelurosaurs. late Jurassic in Utah and adjacent regions. In the The carnosaurs had large and relatively boxy heads, Cretaceous period, after Ceratosaurus died out, the a relatively short neck, and short forelimbs that were tetanurine theropods held exclusive dominion over much smaller than the hind limbs. the predatory ecologic niches in the global dinosaur community. Family Allosauridae As the Tetanurae rose to dominance beginning Allosaurus fragilis in the late Jurassic, many highly specialized lineages Allosaurus was by far the most common the- evolved; the resulting array of derived theropods ropod in Utah during the late Jurassic. This genus became incredibly diverse. Numerous subdivisions name was first formalized by O. C. Marsh in 1877, of the Tetanurae have been established by paleontol- but the animal we describe as Allosaurus also has ogists to accommodate the many specific types. The been referred to as Antrodemus, Poicilopleuron, older terms Carnosauria and Coelurosauria have Creosaurus, Epanterias, and several other names now been redefined in cladistic terms, on the basis coined over the past century. One reason (among of unique sets of derived characters within each several) for the proliferation of names for Allosaurus group. Thus the Carnosauria are no longer consid- is the unusual abundance of this theropod in expo- ered to be just “large” theropods, as opposed to the sures of the Morrison Formation throughout west- “small” Coelurosauria. The carnosaurs and the coe- ern North America. Its remains are so profuse in lurosaurs are viewed as “sister taxa” that proba- Utah that this fierce predator has been designated bly share a common ancestor but are distinguished the official Utah state fossil. At least forty-four indi- from each other by different sets of derived char- viduals of this species are represented by the bones acteristics. It is true, however, that the Carnosauria recovered at the Cleveland-Lloyd Quarry in Emery are mostly larger theropods, while the Coelurosauria County. Although it is much less common at Dino- are mostly small to medium-sized predators more saur National Monument, one of the most spectac- closely related to birds than are the carnosaurs. But ular skeletons of Allosaurus ever discovered came size is not the sole criterion for the definition of from that site in northeastern Utah. Partial skel- these two clades within the Tetanurae. For example, etons or isolated bones of Allosaurus have been several different carnosaurs were relatively small found in dozens of places throughout the eastern predators. This reminds us that the adoption of a and south-central portions of the state. Most Allo- cladistic classification does not mean that we aban- saurus specimens occur in the Brushy Basin Mem- don all older taxonomic groups but simply that we ber, but an articulated specimen has also been can redefine them in ways that are more meaningful discovered in the Salt Wash Member at Dinosaur from the evolutionary perspective. National Monument (Hubert and Chure 1992). The Blood Brothers 127

5.4. Skull of Allosaurus. In comparison to Ceratosaurus, the skull of Allosaurus was deeper, with more numerous openings, such as the maxillary fenestra, a small circular hole between the external nares (en) and the antorbital fenestra (aof). In addition, the teeth do not extend back to the orbit as they do in Cerato- saurus. Based on Madsen 1976b.

amazingly abundant fossils of Allosaurus suggest exhibiting many refinements of the basic theropod that literally swarms of these theropods were pursu- body plan. The skull of Allosaurus (fig. 5.4) was pro- ing prey animals across the Morrison basin for mil- portionally shorter than that of Ceratosaurus but lions of years during the late Jurassic. Partly because was still over 3 feet (1 meter) long in the larger spec- of its extreme abundance in Utah exposures of the imens. As in other tetanurine theropods, the skull Morrison Formation, Allosaurus has become one was lightly constructed, with numerous openings of the best-known dinosaurs ever discovered. Our and hollow cavities. The bones of the skull in front knowledge of the skeletal anatomy of Allosaurus, of the eyes were slender and strutlike, while those presented in such classic works as Madsen (1976a), at the back of the head were more robust. Allosau- surpasses that of all but a few other dinosaurs. In rus seems to have had a few more teeth than did addition, Allosaurus fossils are known from several Ceratosaurus, but they were all positioned far for- different horizons within the Morrison Formation, ward in the jaws, in front of the eye socket. Illustrat- suggesting that it may have been the dominant the- ing this tetanurine trait of concentrating the teeth in ropod in Utah and adjacent regions from about 150 the forward part of the mouth, the bone at the tip of million years ago (at the Cleveland-Lloyd Quarry; the snout in Allosaurus (the premaxilla) bears five after Bilbey-Bowman 1986) to about 130 million teeth, while the same bone has only three teeth in years ago (at the Dry Mesa Quarry in western Col- Ceratosaurus. orado; after Britt 1991), an interval some 20 mil- Allosaurus possessed two prominent brow ridges lion years long. The designation of Allosaurus as the on the lachrymal bone above and in front of the Utah state fossil is certainly no overstatement: it is eyes, with a deep hollow cavity at the base of each. our signature fossil, the consummate prehistoric The lachrymal bone is similar to some of the other animal of the Beehive State. lightweight bones in the skull of Allosaurus in that Allosaurus was the largest common theropod of it has thin walls, hollow pockets, and several small the late Jurassic, with the biggest individuals reach- openings. A very interesting aspect of the skull of ing a length of about 43 feet (14 meters), stand- Allosaurus is the loose joints between some bones ing some 8–9 feet (2.5–3 meters) tall at the hips, at the lower base of the skull (the quadratojugal and weighing at least 2 tons. It was well designed and quadrate) and between several bones compos- for filling the ecologic niche of a large carnivore, ing the back portion of the lower jaw (dentary and 128 Chapter 5

5.5. Skeleton of Allosaurus. Note the S-shaped curve in the neck and the horizontal position of the tail in this running posture. Larger individuals of this theropod were some 40 feet long. Based on reconstruction by Paul 1987. angular-surangular bones). These flexible joints probably allowed Allosaurus to expand the gul- let as it swallowed large chunks of food or perhaps entire animals, in a manner akin to the way modern snakes can ingest objects larger than their heads. Judging from the size and shape of the cervical vertebrae, the neck of Allosaurus appears to have been powerful and quite flexible. The neck appears to have had a natural upward S-shaped 5.6. The right hind foot of curve, however, and was evidently not capable of Allosaurus, seen in oblique being straightened, due to the way the cervical ver- internal view. The hind foot tebrae interlocked (Madsen 1976a). In the shoulder had only three functional toes, each tipped with a region the vertebrae of the backbone have tall neural curving claw. Redrawn from spines and horizontal transverse processes that sug- Gilmore 1920. gest strong ligaments and powerful muscles along the back. The caudal vertebrae have shorter neural the ground in a normal walking or running stance spines and chevron bones than do those of Cerato- (fig. 5.6). The pelvis of Allosaurus is typical of other saurus, indicating that Allosaurus had a less flat- tetanurine theropods in that the bony elements— tened tail, with a more circular cross-section. The tail the paired pubes, ischia, and ilia—are not con- probably projected horizontally behind the hips to sistently and solidly fused. J. H. Madsen (1976a) help counterbalance the body and facilitate changes points out that some of the pelvic bones, especially in direction while Allosaurus was moving (fig. 5.5). the pubes, of Allosaurus from the Cleveland-Lloyd The hind limbs of Allosaurus are massive. The Quarry are fused together, while others are not. Per- largest bone of the hind leg, the femur or thigh haps the variable degree of pelvic fusion represents bone, was bowed slightly toward the front. The cur- sexual differences; females may have possessed the vature of this bone probably allowed it to bend less fused pelvic bones in order to expedite egg- slightly to accommodate some of the stress that laying, similar to the way in which female mam- would have been produced during locomotion. The mals (including humans) loosen the pelvic bones feet of Allosaurus had five toes, though only three as part of the birth process. The overall structure of these supported any weight. Thefift h toe, on the of the hind limbs, pelvis, and back of Allosaurus outside of the foot, was merely a vestigial splint of would clearly have enabled it to run efficiently, but bone, while the fourth toe was too small to reach Blood Brothers 129

5.7. The Cleveland-Lloyd Quarry in Emery County. The hill behind the quarry buildings exposes the mudstones of the Brushy Basin Member of the Morrison Formation. The blocks of sandstone on the lower slopes were eroded from river-deposited sandstone layers near the top of the hill. Photo by Frank DeCourten. its adaptations for speed are less pronounced than or speedy prey such as Dryosaurus. Some paleon- those in several other theropods. tologists have suggested that Allosaurus may have The forelimbs of Allosaurus were small in com- employed pack hunting or ambush strategies to cap- parison to the powerful hind legs. The hands had ture large and/or elusive herbivores. Also, Allosau- only three fingers, each tipped with a sharply rus may selectively have hunted the slower prey pointed and curving claw. But the bones of the fin- animals such as Camptosaurus or Stegosaurus. The gers have many pits and roughened surfaces for the famous Cleveland-Lloyd Quarry in central Utah attachment of ligaments and muscles. These features offers some insight into the feeding behavior of suggest that the forelimbs and hands of Allosaurus Allosaurus, so it is worth a brief pause in our review were useful grasping organs that could develop a of Morrison theropods to explore the nature of this relatively powerful grip. Allosaurus most likely used remarkable fossil accumulation. its hands during feeding, when attacking prey animals, during mating, or on any other occasion that The Cleveland-Lloyd Dinosaur Quarry: An Allosaurus Trap demanded the manipulation of objects. While Allosaurus was a well-adapted preda- The Cleveland-Lloyd Dinosaur Quarry (fig. tor, it does not seem to have had the power or the 5.7) is located about 25 miles south of Price, Utah, speed individually to overtake and subdue the larger and is situated in the Brushy Basin Member of the late Jurassic prey animals such as the sauropods Morrison Formation. Named for the nearby town 130 Chapter 5 of Cleveland and for Malcolm Lloyd, a benefac- late Jurassic forms such as Camptosaurus, Stegosau- tor who sponsored some of the early work at the rus, Camarasaurus, and perhaps a few other herbi- site, this locality has had a long and colorful his- vores. The overall ratio of predator to prey fossils in tory of excavation that encompasses more than sev- the Cleveland-Lloyd Quarry is approximately 3:1. enty years. The various phases in the development The dominance of theropod remains at the of the Cleveland-Lloyd Quarry have been summa- Cleveland-Lloyd quarry is very unusual; by vir- rized by W. L. Stokes (1985), J. H. Madsen (1987), tue of their position at the top of the terrestrial food and W. E. Miller and others (1996). Though the his- pyramid, we would normally expect a very small tory of the quarry is interesting, our main concern number of carnivores to be supported by many her- here is the insights it offers concerning Allosaurus bivorous prey animals. This is certainly the pattern and other Morrison predators. The Cleveland-Lloyd observed among mammals in the modern world Quarry is an exceptional dinosaur locality for sev- wherever natural populations of predators coexist eral reasons. It is no overstatement to refer to it as with their prey. For example, the vast herds of ante- one of the most important fossil sites in the world. lopes and wildebeests in Africa support compara- In recognition of its unique attributes and impor- tively few lions, cheetahs, and hyenas. In a similar tance, the quarry was designated as a U.S. National way, immense numbers of caribou in Alaska and Natural Landmark in 1968. Today it is managed by adjacent regions sustain only a relatively small num- the U.S. Bureau of Land Management, and numer- ber of arctic wolves. These proportions appear to be ous paleontological investigations are still under- reversed at the Cleveland-Lloyd Quarry. For some way. Research at the Cleveland-Lloyd Quarry, and reason many more carnivorous theropods were on the bones it has already produced, will doubtless preserved at this site than would be expected in a continue for many years before the full potential of random sample of the late Jurassic dinosaur com- the site is exhausted. munity. The preservation of dinosaurs at the Cleve- Well over fifteen thousand bones have been exca- land-Lloyd Quarry was clearly, and uniquely, a vated from the fine-grained sediments at the Cleve- nonrandom process. No other Morrison fossil local- land-Lloyd Quarry, among which at least nine ity yields dinosaur remains with such a skewed pro- genera of dinosaurs can be recognized. What is per- portion of predators and prey. Everywhere else haps most remarkable about this quarry is that the across the broad area covered by the Morrison For- vast majority of the bones preserved there belong mation (at Dinosaur National Monument, at Como to theropod dinosaurs. The remains of Allosau- Bluff and the Howe Quarry in Wyoming, and at the rus are the most abundant, with at least forty-four sites in western Colorado) the fossils of herbivo- individuals, ranging in size from small juveniles rous dinosaurs are the most abundant. What spe- to large adults, in the material currently avail- cial circumstances prevailed at the Cleveland-Lloyd able for study. The remains of Ceratosaurus also Quarry to cause the normal predator-prey ratio to have been identified from the site, though they are be shifted so drastically? much less common there than Allosaurus. In addi- The sediments that entomb the bones at the tion, other smaller theropods, such as Marshosaurus Cleveland-Lloyd Quarry offer some clues that help and Stokesosaurus (described later in this chap- us understand the nature of this unique local- ter), are represented by isolated bones collected ity. Unlike those at Dinosaur National Monu- from the Cleveland-Lloyd Quarry (Madsen 1974, ment, the bones at the Cleveland-Lloyd Quarry are 1976b). Fossils representing the herbivorous sauro- preserved in a very fine-grained, clay-rich mud- pods or ornithischian dinosaurs are much less com- stone, interbedded with and capped by thin lay- mon, but they do indicate the presence of familiar ers of limestone. The mudstones contain the clay Blood Brothers 131 mineral montmorillonite, which probably repre- the scene would probably have dashed into the bog sents small grains of volcanic ash that either drifted without hesitation to help itself to a “free lunch.” or were washed into a body of shallow water (Bil- The initial attack would have raised bellows of dis- bey 1992). The matrix surrounding the bones at tress from the Camptosaurus, unable to employ its the Cleveland-Lloyd Quarry has also produced usual methods of evasion. The commotion might the remains of turtles, freshwater snails, and cha- have drawn the attention of other allosaurs in the rophytes, tiny fossils representing a type of green area, who might have joined in the feast. In addi- algae. These accessory fossils provide evidence tion, recall that some paleontologists have spec- of standing water in the area where the dinosaur ulated that Allosaurus, because of its apparent bones became concentrated. None of the bone-pro- inability to outrun swift prey, might have practiced ducing sediments at the Cleveland-Lloyd Quarry group hunting or ambush techniques in acquir- appear to have been deposited by swift rivers or ing prey. Such predatory behavior would certainly large streams, as is the case at Dinosaur National have been useful to the allosaurs that lurked around Monument. Stokes (1985) has suggested that the the bog at the Cleveland-Lloyd site, lying in wait for most likely environment of sediment deposition at approaching herbivores. Once the prey animal was the Cleveland-Lloyd Quarry was a bog or perhaps stuck in the bog, the attacking theropods may have a swampy cove of a shallow lake. Some of the ashy begun to battle each other for a share of the meal. sediments at the quarry contain mineral grains that Something like a feeding frenzy may have ensued, can be dated radiometrically. These dates suggest wherein numerous allosaurs (and other theropods), that the sediments were deposited about 147 mil- large and small, swarmed over the carcass of the lion years ago (Bilbey 1992). poor prey animal that was hopelessly trapped in Thus it is likely that the theropods of the Cleve- the sticky mud. The Camptosaurus in this scenario land-Lloyd Quarry were preserved in a bog or would certainly have met its end, while it is likely swampy pond. But why were so many preda- that at least some of the theropods may have per- tors attracted to this site? The clay in the soft mud ished in battles with each other or sustained mortal would have absorbed water from the bog; when it injuries that prevented them from escaping from the was moistened, the sediment would have been a bog after the attack. sticky, soft, and slippery ooze. Even today, when Such scenarios, in which a single trapped prey these types of sediments become saturated by rain, animal attracted numerous predators, were prob- they are transformed into a mushy gumbo of almost ably repeated many times as the sediments at the frictionless mud. (My truck has been immobilized Cleveland-Lloyd Quarry accumulated. Sometimes by such mud on more than one occasion when I the victim of the attack was a Camptosaurus, while was foolish enough to attempt travel on the dirt at other times it may have been a Stegosaurus or a roads of the San Rafael Swell in a rainstorm.) Any small Camarasaurus. The remains of earlier feed- dinosaur that might have ventured into the bog ing frenzies were trampled and scattered by sub- would no doubt have become deeply mired in the sequent struggles that occurred in the bog. In this soft, slippery mud. Imagine a Camptosaurus bur- manner the skeletons of dinosaurs, both predator ied knee-deep in the Cleveland-Lloyd bog. Slip- and prey, became disarticulated and were dispersed ping and sliding, struggling to extricate itself from throughout the soft mud. This is probably the pri- the slimy ooze, this unfortunate creature would mary reason why the bones found at the Cleveland- surely have attracted the attention of any theropods Lloyd site are rarely articulated (figs. 5.8, 5.9). The in the neighborhood. Taking advantage of a par- bones from this locality do not exhibit any signs tially immobilized prey animal, the first allosaur on of wear that would suggest their transportation in 132 Chapter 5

5.9. Isolated fossil bones from the Cleveland-Lloyd Quarry, positioned as they were found prior to excavation. Photo by Frank DeCourten.

of dinosaur predators in similar portions and may have attracted (and trapped!) Allosaurus and other predators in much the same way as the asphalt in Ice Age California doomed so many carnivorous mammals of that period. We might wonder why the Cleveland-Lloyd her- 5.8. Map of a portion of the Cleveland-Lloyd Quarry. The bivores were drawn into the lethal bog in the first individual bones are almost entirely disarticulated and scattered. From Madsen 1976a. place. What would have enticed Camptosaurus, Stegosaurus, or Camarasaurus, all of which are represented by fossils from the mudstone, to the spot streams or rivers prior to burial. Most of the damage where they met their end? Recall that the climate that has been observed in the bones appears to have across the Morrison basin in late Jurassic time was occurred at death or while the carcasses were dis- probably strongly seasonal, with periods of drought membered by predators or scavengers. alternating with rainy seasons. During the dry inter- Paleontologists generally regard the Cleveland- vals plant food for herbivores would probably have Lloyd Quarry as a “predator trap,” similar in many been concentrated in those places where water ways to the famous Rancho La Brea tar pits of Pleis- remained available as the smaller streams dried up tocene age in southern California. In the tar pits of and the plain became barren and dry. Stokes (1985) California large Ice Age prey animals such as mam- has suggested that the bog or pond at the Cleveland- moths, giant ground sloths, and horses became Lloyd site may have been fed by nearby springs. If mired in the sticky tar that seeped into several this is a correct interpretation, then it is likely that small ponds some 30,000 years ago. The immo- the bog may have contained water even during the bilized prey evidently lured many predators into height of the late Jurassic drought cycles. This is the gummy asphalt. Some 90 percent of the fos- because groundwater is less immediately affected by sils recovered from the tar pits are of carnivorous climatic cycles than is surface water. Even today, in Ice Age mammals such as the sabre-toothed cats regions that experience drought conditions, springs (Smilodon californicus), dire wolves (Canis dirus), often continue to flow for a time after the streams in short-faced bears (Arctodus simus), and others. the area have dried up. As water became scarce dur- The Cleveland-Lloyd Quarry produces the bones ing the Jurassic dry cycles and the vegetation began Blood Brothers 133 to wither, the herbivorous dinosaurs would have that was much larger than Allosaurus. This huge become increasingly desperate for both food and predator is known as Saurophaganax (Chure 1995). water. A spring-fed bog, with its more permanent Its femur was as large as those of some sauropods. supply of water, would have attracted many dino- Saurophaganax was an impressive beast: it was some saurs. Ironically, the dinosaur herbivores may have 36 feet (12 m) long and probably weighed more ventured into the fatal bog as a response to their than 2.5 tons! The vertebrae of Saurophaganax are desperate need for food and water. If so, it was their unusual in that they have ridges and struts of bone survival instinct that ultimately led to their death. that run upward from the base of the neural spines, An interesting twist on the story of the Cleve- a feature not seen in other theropods. Otherwise land-Lloyd site came in 1987, when Dee Hall of the few bones known from Saurophaganax seem to Brigham Young University discovered a nearly com- be much like those of Allosaurus, except for their plete dinosaur egg among the scattered bones of gigantic dimensions. Epanterias, known primar- Allosaurus and other dinosaurs (Madsen 1991). ily from Colorado, Oklahoma, and Wyoming locali- The preserved egg was small, only about 4 inches ties, appears to be another large allosaurid from the (10 centimeters) long, and was crushed so that the Morrison Formation. Epanterias was a very large embryo inside could not be positively identified. theropod, though it was considerably smaller than Allosaurus is by far the most common dinosaur rep- Saurophaganax. The differences between Epanterias resented by the bones excavated from the Cleve- and Allosaurus seem to be very subtle, leading the land-Lloyd site, so the egg most likely belongs to majority of paleontologists to regard the two names this genus. The discovery of the egg was surprising as synonyms for the same animal. Even though because it does not seem likely that dinosaurs would Epanterias and Saurophaganax have not yet been have laid eggs in a muddy bog such as that in which positively identified in Utah and their anatomy is the sediments at this site accumulated. The rela- not well known, it appears that the family Allosau- tively small size of the egg, however, coupled with ridae may have been represented by more than one its occurrence in bog sediments, suggests that the genus during the late Jurassic. The packs of allosaurs egg was never laid. Instead it most likely was devel- that roamed Utah might have been accompanied oping inside the body of a female dinosaur that per- by some very large and terrifying kin: the “Addams ished in the bog. After her death the premature egg Family of the Jurassic.” evidently became preserved along with the bones of the mother dinosaur. This scenario also explains Family Megalosauridae why the embryo within the egg was not identifi- Torvosaurus tanneri able: the egg had not developed long enough for the Torovosaurus is a large Morrison theropod first bones of the baby dinosaur inside to grow to the discovered by Peter Galton and James Jensen (1979) point where the preservation of them was possi- at the Dry Mesa Quarry in western Colorado. Sub- ble. Thus the Cleveland-Lloyd egg was most likely a sequently it has been identified from bones pre- premature embryo carried into the bog by a female served at Dinosaur National Monument in Utah dinosaur. It was probably not laid in the muddy sed- and from two localities in Wyoming (Britt 1991). iments in which it was found. The genus was originally based on only a few bones, Aside from Allosaurus, other members of the but our understanding of the anatomy of Torvo- family Allosauridae may have been present in west- saurus was greatly improved by the work of B. B. ern North America during the late Jurassic. In the Britt (1991). Still, paleontologists remain divided panhandle of Oklahoma the Morrison Formation on how to classify Torvosaurus at the infraorder has produced a few bones of a gigantic theropod or family level. For example, Britt (1991) considers 134 Chapter 5

concave sockets developed on the rear of each neck vertebra to receive the forward-facing balls. This suggests that Torvosaurus had a very flexible neck. The cervical vertebrae were lightened by deep lateral pockets (pleurocoels) on the sides and air- filled chambers inside. The vertebrae of the back were also connected to one another with ball-and- socket joints. The length of the tail is unknown, but it was probably about as long as the tail of Allosau- rus (Britt 1991). No complete hind limbs are known for Torvosaurus, but from the available fragments they appear to have been similar to the general theropod design, with muscular thighs that tapered to 5.10. Skull of Torvosaurus. This reconstruction is based a slender foot. on bones (shaded) collected from western Colorado. Torvosaurus remains are much less common in The total length of the skull is 45 inches. For comparison, the lower jawbone (dentary) of an average Allo- the Morrison Formation than are those of Allosau- saurus, drawn at the same scale, is represented below. rus. Even though Torvosaurus was widely distrib- Based on reconstruction of Britt 1991. uted across the Morrison basin, it would probably not have been encountered very often. Nonethe- Torvosaurus to be a member of the Ceratosauria, less, it would have been a fearsome sight. Most indi- while R. E. Molnar and others (1990) describe it as a viduals of Torvosaurus were significantly larger than possible carnosaur belonging to the Tetanurae. This Allosaurus and were certainly well adapted to pur- uncertainty reflects the generally primitive nature of sue, subdue, and consume large prey animals. Even many of the skeletal features of Torvosaurus; it may the larger prey animals, such as the sauropods, be thought of as either a relatively advanced cerato- would most likely have become alarmed at the sight saur or a relatively primitive carnosaur. of a Torvosaurus. Torvosaurus, however it is classified, was a large and powerful predator. It reached an adult length Family Tyrannosauridae of about 30–35 feet (10–12 meters) and was for the Stokesosaurus clevelandi most part heavily built. The skull (fig. 5.10) was over Among the many bones excavated at the Cleve- 3 feet (1 meter) long, with a relatively narrow snout. land-Lloyd Quarry during the early 1960s were The upper and lower jaws contained about sixty two ilia (bladelike hip bones) and a premaxilla large bladelike teeth, up to 6 inches (15 centimeters) (bone at the tip of the snout) that clearly belonged long (!) that were all positioned in front of the orbit, to the Theropoda but were different from those of as in the Tetanurae. As in the case of Ceratosaurus, any known late Jurassic species. James H. Mad- however, the skull lacked the additional opening sen Jr. described these unique elements in 1974 as (the preantorbital fenestra) seen in most tetanurine a new species and genus, Stokesosaurus clevelandi, theropods. named in honor of the late William Lee Stokes, one The body of Torvosaurus was massive, bulky, of Utah’s most renowned geologists, and for the site and muscular. The forelimbs in particular seem where the bones were discovered (Madsen 1974). to have been powerful, with a massive humerus Even though additional material belonging to Stoke- (upper arm bone). The cervical vertebrae were con- sosaurus has been found elsewhere in the Morrison nected by means of “ball-and-socket” joints, with Formation since Madsen’s original description was Blood Brothers 135

family Tyrannosauridae are obscure, Stokesosaurus is an extremely important dinosaur. It may eventually help us understand how this group of amazing predators evolved. Stokesosaurus appears to have been widespread during the late Jurassic, reaching as far as South Dakota (Foster and Chure 2000) and northern Europe (Benson 2008) during the late Jurassic. But it was not a particularly common predator, based 5.11. Left ilium of Stokesosaurus clevelandi from the on the paucity of fossils representing this genus Cleveland-Lloyd Quarry. Note the prominent ridge that rises vertically from the margin of the hip socket or ace- that have been recovered. Only a few fossils of this tabulum. Scale bar = 2 inches (5 cm). Based on a photo- genus have been found, so we can’t be sure about its graph from Madsen 1974. maximum size, limb structure, body proportions, running ability, hunting strategies, and other char- published (e.g., Britt 1991; Foster and Chure 2000), acteristics. The relatively small size of the Stokeso- most of its skeleton remains unknown. Nonetheless, saurus implies that it probably specialized in the it now appears that one of Madsen’s original inter- smaller prey animals that inhabited the Morrison pretations of Stokesosaurus was correct: it represents plain. We will discuss the small animals that Stoke- one of the earliest members of the family Tyran- sosaurus probably pursued later in this chapter. nosauridae, the lineage that would culminate 70 million years later in Tyrannosaurus, the most men- Coelurosaurs of the Morrison Formation acing predator ever to live on land. Even though Stokesosaurus is related to the The Coelurosauria, as redefined by J. Gauthier tyrannosaurids, it was not a large dinosaur. The (1986), include a great variety of generally small and ilium is only about 10 inches (25 cm) long from lightly built tetanurine theropods that are much front to back. The teeth at the tip of the snout were more birdlike as a group than the carnosaurs. As we about an inch long. These observations suggest have seen in the case of Stokesosaurus, not all car- that Stokesosaurus was probably only about 6–8 nosaurs were large predators. Likewise, among the feet (about 2 meters) long, stood a little less than coelurosaurs we find a number of genera that were 3 feet (1 meter) high at the hips, and might have as large as some carnosaurs. It is the unique fea- weighed around 100 pounds. The ilium is distinc- tures of the skull and skeleton of coelurosaurs, not tive in that it has a prominent ridge on the outside their overall size, that are now used to distinguish surface that runs vertically from just above the hip this group from the Carnosauria. While it is beyond socket to the upper edge (fig. 5.11). This ridge may the scope of our discussion to review all the features have divided masses of muscles that were attached that define the Coelurosauria, their birdlike traits to the ilium. The premaxilla of Stokesosaurus held include a light skull with additional openings (espe- four teeth, a trait similar to the tyrannosaurids and cially in the palate), elongated and slender forelimbs different from either Allosaurus (five premaxillary and hands, and feet that are longer and narrower teeth) or Ceratosaurus (three premaxillary teeth). than those of the carnosaurs. Stokesosaurus is most similar to the tyrannosau- The Coelurosauria consist of several different rids that became dominant in the late Cretaceous, groups of birdlike theropods. Most of these groups but it is some 70 million years older than other are best known from late Cretaceous strata, so coe- members of this family. Because the origins of the lurosaurs are not very abundant in the Morrison 136 Chapter 5

5.12. The skull of Ornitholestes. The total length of this small skull was about 6 inches. The bladelike septum (dashed outline) above the nose is suggested by the 5.13. Hand of Ornit- ridges on the nasal bones, but it has not been found holestes. Note the highly completely preserved in actual skulls. Based on recon- elongated fingers and struction of Paul 1988. the reversed form of digit I, the “thumb,” which Formation. But it now appears that at least some of could have been opposable to the other two fin- the late Cretaceous coelurosaur families originated gers. Scale bar = 2 inches in late Jurassic time. Thus the rare coelurosaurs of (5 cm). Redrawn from the Morrison Formation represent some of the ear- Osborn 1916. liest members of their respective lineages. Ornitholestes Cretaceous “raptors” and their relatives known as Ornitholestes was a small and graceful theropod the Maniraptora than of the less specialized coelu- no longer than about 6 feet (2 meters), with a body rosaurs. Some paleontologists (e.g., Carpenter and weight of around 30 pounds. The skull was very others 2005) regard Ornitholestes as an early mani- light, with large openings between the thin-walled raptoran theropod on the basis of its highly spe- bones. The orbit was particularly large, suggest- cialized hand. Only portions of the hind limbs, ing that Ornitholestes had unusually large eyes that feet, pelvis, backbone, and tail of Ornitholestes are might have given it acute vision. The teeth of Orni- known. On the basis of these incomplete remains, it tholestes, placed forward in the jaws, were mostly appears that Ornitholestes was a swift and agile ani- bladelike and serrated like the teeth of other thero- mal. It seems to have been built for speed, though it pods (fig. 5.12). The nasal openings of Ornitholestes was probably not as fast as some of the Cretaceous were very large and evidently were separated by a coelurosaurs. Moreover, its minimal weight proba- blunt crest or blade of bone reminiscent of the nose bly allowed it to change directions easily. These fea- horn of Ceratosaurus. tures suggest that Ornitholestes hunted small and Like other coelurosaurs, Ornitholestes had rela- elusive prey, which might have been captured with tively long forelimbs. The hands bore three fingers, the prehensile hands rather than with the jaws. two of which were very long. The first digit of the The diet of Ornitholestes probably consisted of hand was relatively short and appears to have been small animals such as lizards, mammals, and early opposable to the other two (fig. 5.13). The structure birds. In fact the name Ornitholestes means “bird- of the hand suggests that Ornitholestes had a strong robber” as a reference to this possible mode of grip and at least some ability to manipulate objects. hunting. Perhaps Ornitholestes also lurked around This type of hand is more characteristic of the late the nesting areas of larger dinosaurs, waiting for a Blood Brothers 137

5.14. Reconstruction of the skeletons of Ornitholestes (top) and Coelurus (bottom), two similar small theropods from the Morrison Formation. Based on reconstructions of Carpenter and others 2005. chance to steal a hatchling as a succulent supple- the carnosaurs. The relative fragility of coelurosau- ment to its normal diet. If so, the adaptations for rian material strongly reduces the probability of its speed make perfect sense. After all, if an animal is fossilization, compounding the problem of nondis- going steal babies from the nest of dinosaurs such as covery related to the small size. It is likely that Orni- Allosaurus, it had better be able to run! Imagine the tholestes was more common during the late Jurassic pursuit that might have followed the theft of such than the relatively rare fossils preserved in the Mor- a hatchling by Ornitholestes. Clutching the shriek- rison Formation might suggest. Russell (1989) has ing baby in its hands, the “bird-robber” would race estimated that Ornitholestes might have constituted away while the mother allosaur followed, franti- about 6 percent of the dinosaurs present during cally trying to save her offspring. If, with her longer the late Jurassic in North America, even though its stride, she managed to gain ground on the fleeing remains represent only 0.6 percent of the fossils col- Ornitholestes, the thief would probably veer sharply lected from rocks of this age. These estimates make to one side while the less agile allosaur stumbled to some sense because many more small animals than redirect its pursuit. After a time the allosaur would large animals are usually present in modern terres- become exhausted from the chase while Ornit- trial vertebrate communities. Ornitholestes, along holestes disappeared over the horizon to find a safe with its other coelurosaurian relatives, were proba- place to consume its stolen meal. bly fairly common in Utah during the late Jurassic. Ornitholestes was first discovered in Wyoming in Coelurus 1900, but little well-preserved and complete mate- Coelurus was a close relative of Ornitholestes. rial belonging to this dinosaur has surfaced since In fact, ever since the first discovery of Coelurus that time. Fragmentary remains of Ornitholestes remains from Wyoming in the late 1870s, paleontol- are now known from several sites in Colorado and ogists have been debating whether or not Coelurus possibly from the Cleveland-Lloyd Quarry (Stokes and Ornitholestes represent the same genus. More 1985) in Utah. But we should recall that the fossils recent studies of the available fossil material of these of small dinosaurs are much less likely to be dis- two genera by J. H. Ostrom (1980) and Carpenter covered than are the remains of larger creatures. In and others (2005) have concluded that they are not addition, the bones of Ornitholestes and other coe- the same dinosaur but quite similar. This historical lurosaurs were much more delicate than those of debate reflects both the fragmentary nature of the 138 Chapter 5

(Norman 1990). Until more complete material is discovered, we can only regard Coelurus as a small Onitholestes-like theropod that might have been seen occasionally on the late Jurassic plains of western North America.

Family Dromaeosauridae? Marshosaurus bicentesimus The remains of Marshosaurus were first discovered at the Cleveland-Lloyd Quarry and were described by James H. Madsen Jr. in 1976 (Mad- sen 1976b). Britt (1991) has identified Marshosaurus fossils from the Morrison Formation at Dry Mesa in western Colorado and Chure and others (1997) 5.15. Cervical vertebra of Coelurus fragilis, in side view (top) and front view (bottom). Scale bar = 0.75 inch (2 reported it from Dinosaur National Monument. In cm). Redrawn from original sketch by Marsh 1881. spite of its broad distribution in the western United States, this theropod is known only from isolated fossils used to define the two genera and their gen- bones, including the ilium, pubic, and pelvic bones eral similarity to each other. and several tooth-bearing bones of the skull such as Coelurus was a small theropod about 8 feet (2.5 the premaxilla, maxilla, and dentary. Although it is meters) long, 2 feet (0.6 meter) tall at the hip, and difficult to assign Marshosaurus to any specific fam- weighing around 30 pounds. These dimensions ily of theropods with such limited knowledge of the are very close to those of Ornitholestes. Coelurus skeleton, it does not appear to represent any of the was evidently a better runner, however, with lon- groups that we have discussed thus far. Marshosau- ger hind limbs and a lighter, more graceful neck (fig. rus appears to be most similar to various mem- 5.14). The cervical vertebrae are very lightly con- bers of the family Dromaeosauridae, an assemblage structed, with ribs (or rib facets) that are fused to that includes the vicious “raptors” that have become the body of the neck bones in the form of a more familiar in popular culture since the release of the or less cylindrical collar (fig. 5.15). The caudal ver- movie Jurassic Park in 1993. Some uncertainty per- tebrae are unusual in that they have large internal sists concerning the family-level classification of air spaces. These hollow tail bones provide the basis Marshosaurus, however, and some paleontologists of the name of the genus: Coelurus means “hol- (e.g., Molnar and others 1990; Benson 2010) assign low tail.” The skull of Coelurus is not well known, it to other taxonomic categories or consider its rela- but the fragmentary bones available suggest that its tionships uncertain (Chure and others 2006). If it is head was more slender and delicate than the skull a “raptor,” Marshosaurus is the earliest known mem- of Ornitholestes. Fossils of Coelurus are extremely ber of its lineage to appear in Utah. As we will see in rare in the Morrison Formation, and what has been the next chapter, the Dromaeosauridae become well recovered is fragmentary. Thus the classification of established in Utah in the early Cretaceous, some Coelurus at the family level remains in doubt and 30 million years after the Morrison sediments were paleontologists are still unsure about its relation- deposited. ships with other coelurosaurs. In addition to the Marshosaurus was a medium-sized thero- original Wyoming discovery, it has been identified pod; with an average length between 15 and 20 feet in Colorado (Gilmore 1920; Britt 1991) and in Utah (5–6.5 m), it was about twice as large as Coelurus Blood Brothers 139

The family Ornithomimidae (“bird-mimickers”) includes some very interesting coelurosaurs that probably looked much like large reptilian ostriches. The ornithomimids had very long hind limbs, with extremely elongated mid-foot bones (metatarsals). The great lengthening of the metatarsals lifted the ankle high above the ground, as in an ostrich or emu, and increased the stride of these swift predators. The forelimbs of the ornithomimids are very long and slender, with elongated fingers. The long arms and hands would have been much more useful in grasping and manipulating objects than were the stubby forelimbs of the carnosaurs. Ornithomimid skulls are small and narrow but have a relatively 5.16. Pelvis of Marshosaurus bicentesimus, from the large braincase and enlarged eye sockets. All orni- Cleveland-Lloyd Quarry of Emery County, Utah. Scale thomimids had a toothless beak that contributed to bar = 2 inches (5 cm). Redrawn from Madsen 1976b. their general birdlike appearance. The edges of the beak appear to have been very sharp, capable of cut- or Ornitholestes. The pubic bone has a slight for- ting through animal flesh just as hawks and eagles ward curve and small “boot” that is unlike that of use their beaks to rip prey animals apart without the other late Jurassic theropods (fig. 5.16). Marshosau- aid of teeth. rus appears to have had more teeth than Allosaurus The ornithomimid theropods are most common or Ceratosaurus, and the details of their serrations in the late Cretaceous, but the earliest members of and placement in the jaw are different from those of this group seem to have made their appearance in the larger theropods (Madsen 1976b). The detailed North America in the late Jurassic. Galton (1982) morphology of the premaxilla and maxilla of Mar- reported the occurrence of Elaphrosaurus, a prim- shosaurus and the way they were joined to each itive ornithomimid, in the Morrison Formation of other are similar in some respects to the “raptors” Colorado. Only the upper arm bone (humerus) of Deinonychus and Velociraptor, but the bones of Mar- Elaphrosaurus was found at the site, and very little shosaurus are larger. In addition, Deinonychus and material belonging to this genus has surfaced from Velociraptor are both Cretaceous theropods and are the Morrison anywhere else. Our knowledge of much younger than Marshosaurus, casting some Elaphrosaurus is derived mainly from African speci- doubt on the closeness of their relationship. Mar- mens and suggests that it was a graceful animal with shosaurus may not have been the only dromaeosaur long, slender limbs. The toes and fingers of Elaphro- inhabiting the Morrison plain during the late Juras- saurus were also elongated. The size and shape of sic. Britt (1991) discovered several teeth that have the ilium and humerus are different in Elaphrosau- dromaeosaur affinities at Dry Mesa in western Col- rus than in other ornithomimids, however, leading orado, but the precise identity of the tooth bearers some paleontologists (e.g., Barsbold and Osmól- cannot be established until more remains of them ska 1990) to consider its family-level classification are found. uncertain. Even though it has not yet been positively identified from Utah, the occurrence of Elaphrosau- Family Ornithomimidae rus in the Morrison Formation of the Rocky Moun- tain region is significant for two reasons. First, it 140 Chapter 5 adds support to the idea of a high degree of faunal interchange between North America and Africa during the late Jurassic. Second, it suggests that the ornithomimids might have originated in North America long before the late Cretaceous, when their remains became much more abundant.

Family Troodontidae Koparion douglassi A relatively recent discovery of a new dinosaur predator from the Morrison Formation was 5.17. A tiny tooth of Koparion douglassi from the Mor- announced in 1994 by paleontologist Daniel Chure. rison Formation of Dinosaur National Monument. Scale Koparion douglassi (Chure 1994) was named on the bar = 0.04 inch (1 mm). Based on photograph in Chure basis of teeth discovered in the Brushy Basin Mem- 1994. ber at Dinosaur National Monument. Though this genus and species is based on a single small tooth body size (known as the EQ or encephalization quo- (fig. 5.17), it is clearly different from those of any tient) of any known group of dinosaurs. The large other theropod known from the Morrison prior to orbits (eye sockets) of the troodontids faced more Chure’s discovery. Koparion had tiny teeth, less than directly forward than did those of any other group 0.1 inch tall. The tooth is recurved toward the rear of dinosaurs, suggesting that they had excellent ste- and has small denticles lining the front and back reoscopic vision and could see very well in dimly lit edges. The largest denticle is positioned at the apex habitats such as the shadowy floor of Mesozoic for- of the tooth and is aligned with the smaller denti- ests. In such environments the good depth percep- cles along the back edge of the tooth. The crown of tion afforded by the placement of their eyes would the tooth has a slight constriction at its base (Chure also have been advantageous in finding and seizing 1994). These details of such a tiny tooth may seem prey animals that might have scampered through trivial, but they are very important. They not only the tangle of shrubs and limbs. serve to distinguish this tooth from those of all These specialized characteristics of the troodon- other Morrison theropods but also document the tids seem to suggest an “intelligent” theropod, a presence of a new family of predators among the selective predator that hunted small animals in for- Morrison carnivores: the fascinating troodontids. ested settings where good visual acuity, agility, and The troodontids (Troodontidae) are a rare fam- cunning would have been necessary to catch prey. ily of theropod dinosaurs formerly known only Was Koparion an “intelligent” dinosaur? Until more from the Cretaceous strata of North America and of its skull and other parts of the skeleton are found, Asia (Osmólska and Barsbold 1990). The troodon- we can’t be sure. If the rest of its skeleton is as simi- tids were small and highly specialized theropods lar to the troodontids as are its teeth, however, then with very long hind limbs, grasping forelimbs, and a Koparion probably could easily have outwitted any very lightly constructed skull. All troodontids have of its contemporaries of the late Jurassic. Kopar- many small teeth, with relatively large hooked den- ion might have lurked motionless in the shadowy ticles similar to those of Koparion. The brain case forests on the Morrison plain of Utah, its glisten- of the troodontids was very large relative to their ing reptilian eyes watching for movement among body size. In fact these dinosaurs were the “braini- the leaves. No motion would have gone unde- est” of all: they had the highest ratio of brain size to tected: it would have responded to the slightest Blood Brothers 141 rustling. Moving silently forward, its head bobbing of Utah, but their remains are usually very fragmen- and weaving to keep the small prey in sight, Kopar- tary. The fossils of amphibians (such as frogs and ion might have deliberately approached its unsus- salamanders) are very rare in the Morrison Forma- pecting target from a direction calculated to conceal tion, but they do occur in places (Chure and Engle- its approach. At just the right instant it might have mann 1989) along with fossils of snails and clams lunged toward the animal, grasped it in its dex- (Gorman and others 2008). Several different kinds trous hands, and held the wriggling creature before of fish are known from the Morrison Formation, its large eyes. Koparion might have paused momen- including lungfish, freshwater sharks, and heavily tarily as it rolled the prey around in its hands. Was scaled bony fish (Kirkland 1987; Chure and Engle- it studying the animal, deciding whether to eat it or mann 1989). Though none of the Morrison coelu- release it? Was it “thinking” at all? Maybe. rosaurs exhibit adaptations for exclusive fish eating, they might occasionally have taken advantage of Coelurosaur Cuisine: Small Animals fish left stranded when ponds or lakes dried up. of the Morrison Formation Also, trace and body fossils yield good evidence that Even though the small carnivorous coelurosaurs many kinds of insects swarmed over the Morrison are not particularly common in the Morrison For- basin in Utah, Colorado, and Wyoming (Hasiotis mation, there are enough indications of their pres- 2004; Gorman and others 2008; Smith and others ence that we might wonder what specific animals 2011). The insect fauna included soil bees, termites, they captured as food. None of these smaller the- crickets, and various aquatic insects. ropods from the late Jurassic of Utah seem to have No bird fossils have yet been positively identified been capable of successfully attacking the large prey from the Morrison Formation, but such fossils are animals, even if they hunted in groups or packs. exceedingly rare in rocks of any age owing to their Instead the large herbivores such as Camptosau- typically delicate construction. Nevertheless, pale- rus, Stegosaurus, and the sauropods were probably ontologists suspect that birds were well established the prime targets of the larger dinosaur predators. by the late Jurassic and that several different kinds A stegosaur would probably have had little to fear of birds may have soared through the Utah skies from Koparion or Ornitholestes. in the company of flying reptiles known as ptero- In addition to dinosaur fossils, the Morrison For- saurs. At least seven different kinds of pterosaurs mation in Utah and nearby regions has produced have been identified from fragmentary remains the remains of many different small creatures that preserved in the Morrison Formation in the Utah might have been pursued by the coelurosaurs. Tur- region (Foster 2003; Chure and others 2006). These tles were evidently common in the ponds, lakes, largest of these birdlike reptiles had a wing span of and streams of the late Jurassic plain. For example, nearly 8 feet (2.5 m), but most were much smaller. two different turtles, Glyptops plicatus and Dino- In addition to these small creatures, ratlike mam- chelys whitei, are known from Dinosaur National mals appear to have been relatively common in the Monument (Chure and Englemann 1989; West and Morrison basin during the late Jurassic, though Chure 1984). These turtles or close relatives are they are known primarily from tiny isolated teeth. known from many other sites in the Morrison For- Nonetheless, the assemblage of primitive mammals mation throughout Utah and Colorado. In addi- included at least twenty-one different genera (Foster tion, the remains of lizards and snakes are also fairly 2009), such as the multituberculates, triconodon- common in the Morrison Formation (Callison 1987; tids, and symmetrodontids, among others (Cle- Prothero and Estes 1980). Several different croco- mens and others 1979; Prothero and Jensen 1983; diles are also present in the late Jurassic sediments Chure and Englemann 1989; Bakker and Carpenter 142 Chapter 5

Thus it appears that the small coelurosaurs might have survived on a mixed diet of ratlike mammals, lizards, snakes, and perhaps even birds, pterosaurs, fish, young crocodiles, and insects. Catching such small prey would require specializations much different from those necessary for pursuing the great herds of sauropods or subduing a large stegosaur. The coelurosaurs of the Morrison Formation, in contrast to the large carnosaurs and ceratosaurs, had to be quick, agile, dexterous, and perhaps even “smart” to survive 5.18. Inner view of the teeth and lower jaw of Zofiabaatar by catching and consuming such small, evasive, and pulcher, a multituberculate mammal from the Morrison easily concealed prey. As we will see in the coming Formation. Note the scale bar (0.04 = 1 mm), indicating that this entire jaw was about half an inch long. Redrawn chapters, this fundamental dichotomy between large from Bakker and Carpenter 1990. and powerful carnivores and small and crafty predators persisted until the end of the Mesozoic, but with 1990). As the names of these groups of mammals different genera filling the two roles. In spite of their suggest, each is distinguished by the unique mor- prominent differences, the hulking carnosaurs and phology of its teeth (e.g., fig. 5.18). None of the mam- the lithe coelurosaurs were collaborators in maintain- mals known from the Morrison Formation appeared ing the ecological balance between predators and prey to have weighed more than about 6 ounces, the size across the Morrison lowland of Utah. Together they of a large mouse (Foster 2009). Such small creatures limited the populations of the large and small herbi- might have been an important food source for the vores to sustainable levels for at least 10 million years. small and agile coelurosaurian theropods. They were the “blood brothers” of the Jurassic. Chapter 6 The Early Cretaceous The (Un)Missing Links 06 When the Jurassic period ended, about 144 million years ago, eastern Utah was populated by a diverse array of dinosaurs. The great sauropods moved across the Morrison plain in herds and as solitary individuals, while other dinosaur herbivores foraged in the more heavily forested areas. Using a variety of hunting strategies and anatomical specializations, the large and small theropods maintained the overall ecological balance by preventing herbivore overpopulation through predation. The rivers flowing from the distant highlands carried sand, silt, and mud into the basin, depositing it across the lowlands in different places at different times as their courses continually shifted in response to seasonal changes in the climate and the undulations of the landscape. This ecosystem had been operating 6.1. Generalized stratigraphy of the Morrison and Cedar Mountain Formation of east-central Utah. A major for millions of years when the sun rose on the first unconformity separates these two formations almost day of the Cretaceous, and nothing seems to have everywhere in the northwest Colorado Plateau region. changed very much with that event. In fact the Jurassic-Cretaceous boundary is often precise as other methods of determining the ages of difficult to identify in the sedimentary sequences volcanic ash. Nonetheless, the dates provide at least of the Colorado Plateau region. In places it appears a suggestion that the sediments of the upper por- that the sediments of the Brushy Basin Member tion of the Morrison Formation may be early Creta- of the Morrison Formation continued to accumu- ceous in age. late well into the earliest part of the Cretaceous Whatever the exact age of its uppermost layers period. For example, B. J. Kowallis and others (1986) may be, the Morrison Formation is always capped and Kowallis and J. S. Heaton (1987) have reported by a surface of erosion, an unconformity, that sep- ages as young as 125 million years for zircon crys- arates it from the overlying strata. Sometimes the tals from the volcanic ash of the Brushy Basin Mem- unconformity at the top of the Morrison Formation ber in the area around Capitol Reef National Park in is a distinct undulating surface with several feet of central Utah. These dates are based on the density of relief that truncates the layers beneath it (fig. 6.1). tiny defects in the crystals produced by subatomic In other places the unconformity is so subtle that it particles ejected from the nucleus of radioactive might be easily overlooked without careful inspec- atoms such as uranium. Known as fission-track dat- tion. In most localities in eastern Utah several hun- ing, this technique is not always as reliable or as dred feet of soft mudstone and sandstone rest on

143 144 Chapter 6 the unconformity at the top of the Morrison For- First, the color banding in the Cedar Moun- mation. These overlying sediments are generally tain Formation is usually less prominent than it is similar to those of the Brushy Basin Member and in the Morrison Formation. The Cedar Mountain are known throughout most of Utah as the Cedar mudstones generally have a drab gray or pale pur- Mountain Formation, named by Stokes (1944, 1952) ple color in contrast to the bright red, white, lav- for the highest point in the northern San Rafael ender, and gray of the upper part of the Morrison Swell of Emery County. East of the Colorado River, Formation. In addition, the relatively broad and in extreme eastern Utah and western Colorado, faded bands of color in the Cedar Mountain Forma- similar sedimentary rocks overlying the Morrison tion are usually less distinct than those of the Mor- Formation are referred to as the Burro Canyon For- rison. These differences in color banding render the mation. As an expression of the overall similarity of Cedar Mountain badlands much less scenic than the the Cedar Mountain/Burro Canyon sequence to the spectacular Morrison landscapes. Few tourists waste underlying Morrison sediments, these two forma- any film photographing Cedar Mountain badlands, tions were commonly mapped together as one unit and no Hollywood producer has ever used them as prior to Stokes’s detailed study. a backdrop for westerns. Because the Cedar Mountain Formation and Gastroliths (the smooth and rounded stones that the Morrison Formation are so similar in gen- may represent the “gizzard stones” of dinosaurs) eral appearance and the unconformity separating occur from place to place in the Morrison Forma- them may be subtle and indistinct, people exploring tion but are much more abundant in the Cedar Utah’s dinosaur country often have difficulty distinguishing the two formations. Only in the northern San Rafael Swell area, where about 50 feet of coarse conglomerate separates the Morrison For- mation from the Cedar Mountain Formation, is it easy to identify the boundary between the two rock units. This pebble-cobble conglomerate was named the Buckhorn Conglomerate Member (of the Cedar Mountain Formation) by Stokes (1944, 1952) for the area around Buckhorn Reservoir, east of Cleve- land, Utah. The Buckhorn Conglomerate is not very widely distributed, however, and either disappears or thins to an inconspicuous sandstone layer beyond the northern San Rafael Swell area. In many places throughout eastern Utah the soft mudstones of the main body of the Cedar Mountain Formation rest directly on similar materials of the uppermost Morrison Formation. But a careful examination of the sediments in these units in these areas will reveal some differences that not only are useful in dividing the rock succession but also provide some 6.2. Gastroliths weathering out of the dray mudstones of important clues about the conditions during the the Cedar Mountain Formation in Emery County. Cour- early Cretaceous in east-central Utah. tesy John Telford. The Early Cretaceous 145

Mountain Formation. In places the weathered sur- In addition, nodular masses of nearly pure calcite faces developed on exposures of the Cedar Moun- are extremely common in certain horizons in the tain Formation are littered with hundreds of highly Cedar Mountain Formation. These small nodules polished gastroliths, many with brilliant colors (fig. commonly weather out of the enclosing mudstones 6.2). The extreme abundance of gastroliths in the and accumulate on the surface as a loose blanket of Cedar Mountain Formation can sometimes be help- small, irregularly shaped rocks. These calcite nod- ful in distinguishing it from the underlying Morri- ules often make maneuvering over Cedar Mountain son Formation. Exactly why gastroliths are so much slopes treacherous: it’s a bit like trying to walk on a more abundant in the Cedar Mountain Formation slope covered with marbles! In addition to the cal- remains a bit of a mystery. Though that formation careous nodules, the Cedar Mountain Formation has produced the remains of several different types has many more thin layers of solid limestone, com- of dinosaurs, fossils of sauropods (the dinosaurs posed almost entirely of calcite, than in the underly- most likely to have possessed gizzardlike organs) are ing Morrison sediments. Thus the Cedar Mountain not particularly common. Perhaps many of the gas- Formation contains much more calcareous mate- troliths that occur in the Cedar Mountain Forma- rial, in several different forms, than is present in the tion are not “gizzard stones” at all; they may have Morrison Formation. developed their smooth form and polished surfaces The significance of this increase in calcareous by some mechanism other than gastric tumbling in minerals is that it may be a reflection of changes the belly of a dinosaur. However they originated, the in both the climate and the geography during the great abundance of gastroliths is a unique character- early Cretaceous period. Calcite and other carbon- istic of this early Cretaceous formation. ate minerals form abundant nodules in soils that There is also a subtle but very important differ- develop from sediment under warm and dry cli- ence between the composition of the mudstones matic conditions in the modern world. In many that make up most of the Cedar Mountain For- desert regions the formation of calcite in the soil mation and the rocks of the underlying Morrison leads to the development of caliche, a crusty mass of Formation. In the upper part of the Morrison For- calcium carbonate. Caliche forms in the soils of arid mation (the Brushy Basin Member) the mudstones regions both as irregular lumps and as wavy layers are composed primarily of clay minerals such as known as “hardpans.” Both types of calcite are com- montmorillonite and illite, with minerals such as mon in the Cedar Mountain Formation. Based on quartz and feldspar representing a small fraction of the shift to more calcareous sediments in this for- the fine-grained sediment. Calcite, a mineral com- mation, it seems plausible to conclude that the cli- posed of calcium carbonate (CaCO3), exists but is mate of the early Cretaceous became more arid than not usually very common in the Morrison mud- it was during most of the preceding late Jurassic. If stones. In the overlying Cedar Mountain mudstones, we examine the geological events that were taking above the unconformity that caps the Morrison For- place in adjacent regions of North America during mation, the mudstones are usually much richer in the early Cretaceous, we can identify some reasons both calcite and dolomite, CaMg(CO3)2, a similar why this change in climate might have occurred. calcium-bearing mineral. The abundance of these The hilly terrain in western Utah and eastern minerals in the Cedar Mountain deposits has led Nevada began to experience more serious geologi- geologists to refer to them as calcareous mudstones, cal disturbances after the end of the Jurassic period meaning that the clay minerals are accompanied by (Schwans 1987). Numerous studies of the early Cre- significant amounts of calcium-bearing compounds. taceous paleogeography and tectonics of the eastern 146 Chapter 6

Great Basin region (Allmendinger and others 1985; Cowan and Bruhn 1992) suggest that compressional forces were intensified about 120 million years ago. The enhanced compression led to the crumpling of rock layers and the formation of low-angle thrust faults in the region around the Raft River Range of northwest Utah, in the northern Wasatch Moun- tains area, and elsewhere in the eastern part of the Great Basin. This deformation, related to the compressive stresses produced by the subduction of an oceanic slab of rock beneath the western edge of North America, accelerated the uplift of the eastern Great Basin region that began in the late Jurassic. As the mountainous terrain rose, the older Mesocor- dilleran High was elevated to become a more prominent highland bordering the interior lowland of eastern Utah. 6.3. Early Cretaceous paleogeography of the Utah region. The Sevier Orogenic Belt was a rugged high- The higher ground in eastern Nevada and west- land in eastern Nevada and western Utah that created ern Utah pirated moisture from storms pass- dry conditions in the interior basin to the east. Yellow ing inland from the west coast, just as the modern symbols indicate the approximate position of some of Sierra Nevada in California creates a rain shadow the dinosaur localities in the Cedar Mountain Forma- tion: 1. Price River Quarries; 2. Rough Road Quarry; 3. desert across most of present-day Nevada. Little Long Walk Quarry; 4. Southern San Rafael Swell; 5. Gas- moisture remained in the air masses that passed ton Quarry; 6. Dalton Well Quarry; 7. Dinosaur National over the early Cretaceous highland into the Colo- Monument. Reconstruction from Ronald Blakey/Colo- rado Plateau region. As the rains became less fre- rado Plateau Geosystems, Inc. Used with permission. quent in central and eastern Utah, the increasing aridity led to the precipitation of calcium carbonate Mesocordilleran High of the late Jurassic developed in the soils of the interior basin (Ludvigson and oth- into the Sevier Orogenic Belt. ers 2010). The pulse of early Cretaceous uplift that In addition to enhancing the aridity of eastern led to the shift toward drier conditions in central Utah, the pulse of uplift that affected the land in Utah marks the transition of the Mesocordilleran western Utah during the early Cretaceous also lifted High into what geologists call the Sevier Orogenic the stream beds that were draining into the inte- Belt (fig. 6.3). Even more intense deformation would rior basin. In response, the rivers cut deeper chan- follow in the late Cretaceous as the Sevier Orogenic nels through the rising land and scoured away at Belt evolved into a magnificent mountain system least some of the sediments that had been deposited (see chapter 7). Henceforth I will refer to the high- earlier. In time, as the rivers shifted back and forth lands of western Utah and eastern Nevada as the across the land, a broad erosion surface was devel- Sevier Orogenic Belt, even though it was not nearly oped. This surface of erosion is represented by the as prominent in the early Cretaceous as it would regional unconformity that in many places separates become some 30 million years later. As we shall the Morrison Formation from the Cedar Mountain soon see, the early Cretaceous was a time of numer- Formation. The rivers descending from the Sevier ous transitions in the land and life of Utah. The first Orogenic Belt ran swiftly to the east down beds of those transitions occurred in western Utah as the steepened by the uplift that was occurring in their The Early Cretaceous 147

6.4. Outcrops of the Buck- horn Conglomerate Mem- ber of the Cedar Mountain Formation near Buckhorn Reservoir, Emery County. Courtesy John Telford. headwater regions. Flowing with greater energy, The Buckhorn Conglomerate Member is not par- the rivers could transport large pebbles and cob- ticularly widespread in central Utah. Beyond the bles well beyond the eastern flanks of the Sevier northwest San Rafael Swell region, where this mem- Orogenic Belt. Eventually the streams flowed out of ber was first defined, no massive conglomerates the mountainous terrain and across the gullied and are present in the Cedar Mountain Formation. In scoured floor of the interior basin to the east. The places where the Buckhorn Conglomerate is miss- pebbles and cobbles accumulated on this undulating, sheets of coarse, river-deposited sandstone ing surface as the streams joined to form languid commonly rest above the Morrison-Cedar Moun- rivers that lacked the energy to carry the rubble any tain unconformity. Thus it appears that the Buck- farther. The Buckhorn Conglomerate Member of horn Conglomerate represents a local accumulation the Cedar Mountain Formation originated from the of pebbles and cobbles that was deposited where accumulation of such materials transported from the east-flowing rivers first encountered the flat- the highlands to the west. The smooth and rounded lands. In that area, where the flanks of the Sevier stones of the Buckhorn Conglomerate Member (fig. Orogenic Belt met the interior basin, a moundlike 6.4) clearly show the effects of river transport and alluvial fan complex developed. Beyond this pile of are primarily composed of chert and quartzite that gravel the streams transported smaller sand-sized sometimes have Paleozoic fossils preserved in them. grains across the broad floor of the basin, eventu- Such rock is a perfect match for the layers that were ally depositing them on the eroded outcrops of the involved in the early Cretaceous deformation to the underlying Morrison Formation. Ultimately, as the west as the Sevier Orogenic Belt emerged. In addi- uplift of the Sevier Orogenic Belt subsided (tempo- tion, the orientation of the pebbles in the Buck- rarily), the eroded land in the basin was built up by horn Conglomerate suggests that most of them were the accumulation of layers of sand and gravel, while deposited by streams flowing into central Utah from the rivers cut deeper channels into the highlands to the west or southwest (fig. 6.3). the west. These two factors, erosion in the highlands 148 Chapter 6 and deposition of sediment in the basin (known to Mountain mudstones buried hills carved into Mor- geologists as aggradation), reduced the slope of the rison mudstones. stream channels. In response to the reduced slope of The main body of the Cedar Mountain Forma- the stream beds, the rivers became more lethargic. tion above the Buckhorn Conglomerate Member has As the early Cretaceous progressed, the now- been subdivided into four members (Kirkland and sluggish rivers deposited fine silt and mud on others 1997) (in ascending order): the Yellow Cat top of the coarse sand and gravel dispersed ear- Member, Poison Strip Sandstone, Ruby Ranch Mem- lier across the basin floor. Much of this fine sedi- ber, and Mussentuchit Member (fig. 6.5). All of these ment was deposited across the plain during flood members are named for Utah localities and reflect events when the rivers breached their channels and the varied nature of the mostly fine-grained sedi- spread out laterally over great distances. Thus the ments that were deposited after the Buckhorn Con- upper portions of the Cedar Mountain Formation glomerate was laid down. The distinctions between are composed almost entirely of calcareous mud- these various members of the Cedar Mountain For- stone that accumulated on the floodplains border- mation involve subtle features such as the composi- ing the slow streams. In time even the highest hills tion of the clay minerals, the relative abundance of of the basin were buried under the mud and silt. In volcanic ash, and the amount of carbonaceous mate- such areas the Cedar Mountain Formation would rial in the sediments. A complete discussion of the be relatively thin and would rest directly on fine- various members of the Cedar Mountain Forma- grained mudstones of the Morrison Formation. It tion is beyond our scope here, but many additional would not be easy to find the boundary between details can be found in Kirkland, Cifelli, and others the two formations in these locations, where Cedar (1997) and Kirkland and Madsen (2007).

6.5. Stratigraphy of the Cedar Mountain Formation in east-central Utah, with distribution of some of the newly discovered dinosaurs. The Early Cretaceous 149

Historically the Cedar Mountain Formation the west side of Arches National Park in the 1970s has not been the source of very much information (Galton and Jensen 1979). This quarry is situated a on dinosaurs or other prehistoric creatures. Fos- few meters below the horizon that produced Hopli- sils of any kind are definitely less common in the tosaurus(?), near the base of the Cedar Mountain Cedar Mountain Formation than they are in the Formation. The bones excavated from the Dalton underlying Morrison mudstones. Over the past Well Quarry are still under study, and many more two decades, however, numerous fossil discoveries fossils could potentially be quarried from the site have been made in the Cedar Mountain Formation, in the future. James Jensen described reptilian egg- clearly demonstrating that it is not as “unfossilifer- shell fragments from the Cedar Mountain Forma- ous” as it was often portrayed in the geological lit- tion that were discovered near Castle Dale, Utah, erature of the 1950s and 1960s. It seems that one on the west side of the San Rafael Swell (Jensen reason why this formation has been overlooked for 1970). In the mid-1980s numerous small fossils were so long is that many paleontologists were so dazzled reported from what became known as the Rough by the abundance of dinosaur fossils in the Morri- Road Quarry, located in the northwest San Rafael son Formation that they spent little time prospect- Swell region east of Castle Dale (fig. 6.3). The Rough ing Cedar Mountain outcrops for fossils. Beginning Road Quarry and several other sites nearby have in the 1980s, however, scientists from the Utah produced an amazing variety of small fossils of both Museum of National History, Utah Geological Sur- terrestrial and aquatic vertebrates. Small dinosaur vey, College of Eastern Utah, University of Okla- teeth, crocodilian and turtle fossils, lizard and fish homa, and other institutions have systematically remains, and the teeth of several primitive mam- searched for fossils in the Cedar Mountain Forma- mals have all been recovered from this quarry (Nel- tion. Collectively this work has demonstrated that son and others 1984; Nelson and Crooks 1987; Eaton the formation is in fact rich in fossils. The newly and Nelson 1991). discovered material represents some exciting new The current surge of interest in the dinosaurs of perspectives on the history of dinosaurs in Utah and the Cedar Mountain Formation began in earnest adjacent regions of North America. At the risk of during the late 1980s, when researchers from the overstating things slightly, the Cedar Mountain For- Utah Museum of Natural History discovered a con- mation of Utah has become one of the most excit- centration of bone in Emery County now known ing horizons in contemporary dinosaur research. as the Long Walk Quarry (fig. 6.3). This site, which It reveals a menagerie of dinosaurs quite unlike the produced mostly fragmentary fossil material, is situ- Morrison fauna and provides evidence of some pro- ated in the lower Ruby Ranch Member of the Cedar found changes in the land and life of Utah during Mountain Formation, about 45 feet above the top of the early part of the Cretaceous period. the Morrison Formation. The Long Walk Quarry is thus intermediate in age between the younger (and higher) Rough Road Quarry and the older (and Dinosaur Faunas of the Cedar Mountain Formation lower) Dalton Well Quarry. Utah state paleontolo- The first formal description of a Cedar Mountain gist James Kirkland, Don Burge, and Ken Carpenter dinosaur was published by N. M. Bodily (1969), who (College of Eastern Utah), and their many collabo- tentatively identified Hoplitosaurus(?), a quadru- rators and volunteers have made many subsequent pedal and armored herbivore, from a site about 20 discoveries in east-central Utah including the Gas- miles north of Moab. The Dalton Well Quarry in the ton Quarry, the Crystal Geyser Quarries, and the same region was developed by scientists at Brigham Price River Quarries (fig. 6.3). In addition, Richard Young University, after bones were discovered near Cifelli of the Oklahoma Museum of Natural History 150 Chapter 6

6.6. Falcarius utahensis: A. skeleton; and B. skull. This A odd therizinosaur is the oldest of the new dinosaurs discovered recently in the Cedar Mountain Formation. Scale bar for skeleton = 39 inches (1 m), total length of skull is about 12 inches. Skeletal reconstruction based on Kirkland and others 2005. has reported dinosaur and other reptile remains accompanying the fossils of small mammals that he found in the upper Cedar Mountain Formation at Mussentuchit Wash in southern Emery County (Cifelli 1993). J. G. Eaton and M. E. Nelson (1991) B have reported additional small mammal remains from the Cedar Mountain Formation along the west side of the San Rafael Swell. The “bone rush” to the youngest, emphasizing how dinosaur communities Cedar Mountain beds over the past few years has changed in Utah from about 125 million years ago to resulted in the discovery of abundant fossils from 98 million years ago. several different localities, documenting the presence of many new species of dinosaurs and illumi- The Yellow Cat Fauna: The Basal Assemblage nating what was heretofore a poorly known period in the evolution of Utah’s dinosaurs (Kirkland and The lower portion of the Cedar Mountain Forma- others 2005; Kirkland and Madsen 2007). tion in eastern Utah is known as the Yellow Cat All of this new information allows us to formu- Member, a sequence of mudstone layers interbed- late a much more complete interpretation of Utah’s ded with limestone and sandstone (fig. 6.5). Over- early Cretaceous dinosaur faunas than was possi- lying the Yellow Cat Member in eastern Utah is a ble only a few decades ago. The story of Early Cre- thin pebbly sandstone sequence known as the Poi- taceous dinosaurs in Utah is still unfolding, of son Strip Sandstone. The strata of these two mem- course, and many new types certainly await dis- bers contain the fossils of the earliest Cretaceous covery in the years to come. Nonetheless, we are dinosaur fauna in the Colorado Plateau region. This beginning to recognize several different faunas that fauna is probably around 120–125 million years old, seem to be restricted to certain horizons within some 20 or so million years younger than the dino- the Cedar Mountain Formation. Kirkland and sev- saurs that occur in the Morrison Formation imme- eral colleagues have suggested that at least two, per- diately below. Elements of the basal fauna have thus haps more, distinct faunas can be recognized among far been found primarily in Grand County in places the dinosaur remains excavated from this forma- such as the Gaston Quarry, the Dalton Well Quarry, tion in Utah (Carpenter and others 2002; Kirk- and other localities near Green River. This oldest land 2005). Let’s review the newly discovered fossils assemblage of dinosaurs from the Cedar Mountain from the Cedar Mountain Formation from oldest to Formation has been referred to as the Yellow Cat The Early Cretaceous 151

6.7. Replica of the skeleton of Utahraptor ostrommaysi at the College of Eastern Utah Prehistoric Museum. Photo by Frank DeCourten. fauna (Kirkland, Britt, and others 1997; Kirkland, long. The forelimbs of Falcarius appear to have been Cifelli, and others 1997), contains at least eight dif- extremely flexible and capable of a wide range of ferent dinosaur genera, and may represent two dis- sophisticated movements (Zanno 2006). Most pale- tinct subassemblages (Kirkand and Madsen 2007). ontologists agree that these unique skeletal features The remains of the oldest dinosaur from the Yel- suggest that Falcarius was probably an omnivore low Cat Member were found in western Grand that acquired plant material or animals selectively County and named Falcarius utahensis by Kirk- through the use of its flexible arms and long fingers land, Zanno, and others (2005). Falcarius belongs and claws. Another intriguing aspect of Falcarius is to a group of odd bipedal dinosaurs known as the that its remains were discovered in a bone bed that therizinosaurs. They are classified as maniraptoran includes fossils of perhaps a dozen or more individ- theropods (typified by the “raptors”) but were prob- uals of various sizes. The unexcavated portion of the ably not strict carnivores, unlike other members bone bed may contain bones belonging to hundreds of that group. The leaflike teeth of the therizino- of individual therizinosaurs that died in the same saurs were small and quite unlike the sharp dag- place at the same time. Thus it appears that Falcarius gerlike teeth typical of other theropods. With tiny foraged over the Cedar Mountain basin in herds or denticles along the tooth margins, Falcarius teeth at least gathered in such groups temporarily at spe- would have been equally useful for shredding plant cific places. No one knows exactly why so many Fal- material or for consuming small prey animals. Fur- carius individuals were entombed together, but the thermore, the pubis of Falcarius did not project deposits that contain their fossils could have accu- strongly forward as in most other thropods but was mulated around a dwindling pond during the dry positioned almost vertically (fig. 6.6). This unique season. If so, thirst and starvation were the likely pelvic architecture would have accommodated causes of the mass mortality of so many Falcarius a greater digestive mass, giving the 12-foot-long individuals. (4-meter) Falcarius a somewhat ungainly pot- Also present in the strata that contain the Fal- bellied appearance. carius bone bed is another small predator named Falcarius also had extremely long fingers, tipped Geminiraptor suarezarum by P. Senter and oth- with curving claws 4–5 inches (10–12 centimeters) ers (2010). Geminiraptor is based on a 4-inch 152 Chapter 6

(10-centimeter) fragment of the upper jaw that the flanks or belly of prey animals. The sharp claws shows features unique to the troodontid group of of the hand were also well suited for grasping prey theropods. As we learned in the last chapter, the by stabbing through the hide with a forceful grip. specialized troodontids were present in North The best-known dromaeosaur from North Amer- America during the late Jurassic, so their appear- ica is Deinonychus, originally discovered in the Clo- ance in the form of Geminiraptor in the early Cre- verly Formation along the Wyoming-Montana taceous is not surprising. The significance of the border. Velociraptor, a diminutive late Cretaceous Geminiraptor is that this small (50 pounds or so) dromaeosaur from Asia, evidently preferred smaller birdlike theropod demonstrates that the dinosaur prey but could still attack creatures larger than itself. population in the Cedar Mountain Basin included A partial skeleton of Velociraptor has been found several different predators and omnivores. still clutching the small ceratopsian Protoceratops. Perhaps the best known predator of the Yel- These two occurrences demonstrate that the drom- low Cat fauna is Utahraptor ostrommaysi (Kirk- aeosaurs were capable of utilizing a wide range of land, Burge, and Gaston 1993), the terror of the early prey animals, including relatively large herbivores. Cretaceous (fig. 6.7). Bones from this large thero- As a group the dromaeosaurs were generally pod were first discovered from the Gaston Quarry rather small animals. Few exceeded about 10 feet in 1991 and 1992 from a sequence of rock layers in (3.3 meters) in length, and full-grown adults gen- the higher portion of the Yellow Cat member, about erally weighed less than 200 pounds. For dra- 15 feet below the overlying Poison Strip Sandstone. matic effect the “raptors” of the movie Jurassic Park, Utahraptor was based on fragmentary fossils repre- based on Velociraptor, were greatly exaggerated in senting parts of the skull, a tibia, and claws from the size (but probably not in attitude). Ironically, at foot and hand. This predator is also present at the about the same time that this popular motion pic- Dalton Well Quarry in the lower Cedar Mountain ture was thrilling audiences everywhere, Utahraptor Formation, where additional claws from the hand remains were being excavated in eastern Utah. What and vertebrae from the tail were preserved. Though emerged from the Gaston Quarry was a dromaeo- these remains of Utahraptor are far from complete, saur of Spielbergian dimensions. Measured along they provide a reasonably good basis from which to the outer curve, the preserved claw on the second reconstruct the basic features of a most fascinating toe of Utahraptor is nearly 9 inches (23 centimeters) theropod. long, almost twice as large as that of Deinonychus Utahraptor is clearly a dromaeosaur (family Dromaeosauridae) or “raptor” in the popular dinosaur literature. The dromaeosaurs were fierce bipedal predators with long and powerful legs, a stiff counterbalancing tail, a large skull carrying many razor-sharp teeth, and greatly enlarged sickle- shaped claws on the second toes of the hind feet. These huge foot claws were raised off the ground while the dromaeosaurs ran but were attached via 6.8. Claw of Utahraptor. Note the prominent groove on ligaments to powerful muscles higher in the leg. the right side of this claw from the second toes of the right foot. This groove helped secure the horny sheath When activated, the large foot talon could rotate that covered the bone, forming a talon over a foot long. downward through a wide arc with great force. Cou- Scale bar = 1 inch (25 mm). Based on a drawing by Rick pled with a raking or kicking motion of their hind Adleman in Kirkland and others 1993. limbs, the dromaeosaurs could inflict deep gashes in (fig. 6.8). The Early Cretaceous 153

In life the bony portion of this foot claw was cov- additional food source. In view of the size and spe- ered by a horny sheath that would have formed a cializations for carnivorous habits observed in Utah- sharp talon about 14 inches (36 centimeters) long. raptor, it is difficult to envision any herbivore that The other preserved elements of Utahraptor (cau- would not have been distressed by the approach of dal vertebrae, premaxilla, foot and hand bones) from even one not to mention a hungry group of these Utah sites are also much larger than their coun- swift, snarling raptors. Utahraptor was the terror of terparts in Deinonychus or any other dromaeosaur the early Cretaceous. (Kirkland, Burge, and Gaston 1993). Based on the The Yellow Cat Member of the Cedar Mountain size of recovered bones, Utahraptor was probably Formation contains hints of other types of pred- around 20 feet (6.5 meters) long and weighed per- ators. Nedcolbertia is a small (about 10 feet [3.3 haps 1,000 pounds. This clearly makes Utahraptor the meters] long) dinosaur known primarily from the largest known dromaeosaur in the world. As Kirk- bones of lower hind limb and foot. This small pred- land, Burge, and Gaston (1993) have suggested, com- ator is a very lightly built theropod that may be an paring Utahraptor to Deinonychus is like comparing a early member of the ornithomimids, a group of polar bear to a jackal, at least in terms of size. ostrichlike toothless predators that became much With such a large body, Utahraptor was clearly more abundant in the late Cretaceous period (Kirk- capable of overpowering and subduing relatively land, Britt, and others 1998). Some scrappy remains large prey animals. This dromaeosaur may not have seem to belong to a larger theropod, possibly related been limited to the pack-hunting techniques that to Allosaurus (Kirkland 2005; Kirkland and Mad- were evidently employed by the smaller members of sen 2007). Thus it appears that many different types its family. Moreover, the hand claws of Utahraptor of dinosaur predators existed during the time when are almost as large as the fearsome foot claw and are the earliest sediments of the Cedar Mountain For- significantly narrower than in most other dromaeo- mation were accumulating in east-central Utah. saurs (Kirkland, Burge, and Gaston 1993). This sug- What were they eating? gests that the hands of Utahraptor had sharp-edged Fossils collected elsewhere in the Yellow Cat claws potentially useful for cutting and ripping flesh Member over the past two decades reveal rich from the carcass of a prey animal. Although we assemblages of herbivorous dinosaurs that might cannot rule out the possibility of pack-hunting for have been prey for the diverse predators mentioned Utahraptor, we have no strong evidence for it. This above. Remains of the armored quadrupedal nodo- large dromaeosaur certainly could have functioned saurs, similar to the European Polacanthus and the effectively as a solitary predator. The early Creta- North American form Sauropelta, have been found ceous basin of eastern Utah probably supported a in several different localities. Nodosaurs (family variety of prey animals that could have been the tar- Nodosauridae of the suborder Ankylosauria) were gets of Utahraptor attacks. Many types of herbiv- fascinating large, squat quadrupedal herbivores orous ornithopods and nodosaurs (described in with dermal armor that covered most of the dor- later sections) would certainly have been tempting sal surface (the neck, back, hips, and tail). None of to Utahraptor. The nodosaurs, even with their pro- the nodosaurs had the tail club that characterizes tected dorsal surfaces, might also have suffered from their later and generally larger relatives in the family Utahraptor assaults, particularly if the powerful car- Ankylosauridae, such as the familiar Ankylosaurus. nivores could overturn them to expose the vulner- The ribs in nodosaurs flared out from the spine in a able belly region. As we shall see, several different nearly horizontal fashion before curving downward small sauropods are also known from the Cedar around their barrel-shaped bodies. This feature gave Mountain Formation and could have provided an the nodosaurs very broad and practically flat backs. 154 Chapter 6

Nodosaurs were common worldwide during the early Cretaceous but in most cases are known only from very scrappy material. In the absence of well-preserved and complete skeletons, many different names have been applied to the fragmentary remains of nodosaurs. This uncertainty is reflected in the queried identification (Hoplitosaurus?) given by Bodily (1969) in his report of the first nodosaur discovered from the Cedar Mountain Forma- tion. While no complete skeleton of any nodosaur has ever been found in that formation in Utah, fragmentary remains and partial skeletons are relatively abundant. Hoplitosaurus? was the first armored dinosaur described from the lower Cedar Mountain Forma- tion (Bodily 1969). The identification was based on many armor scutes of various shapes and sizes, numerous tail vertebrae and armor, and a few partial limb elements. Other paleontologists (e.g., Weishampel 1990) have regarded these fragmentary remains as more similar to Sauropelta, a nodosaur known from the Cloverly Formation of Wyoming 6.9. Replica of the skeleton of Gastonia burgei at the and Montana. Kirkland (1991) reported additional College of Eastern Utah Prehistoric Museum. Photo by nodosaur remains from the lower Cedar Mountain Frank DeCourten. Formation that were similar to both Sauropelta and Polacanthus. Some uncertainty about the precise 2002), so a fairly reliable reconstruction of the anat- identity of the lower Cedar Mountain nodosaurs omy of this dinosaur can be developed. Gastonia still remains. For example, J. Pereda-Suberbiola was a medium-sized, quadrupedal herbivore with a (1994) concluded on the basis of the shape of the total length of about 16 feet (about 5 meters), weigh- plates on the tail and the height of the neural spines ing about a ton or so (fig. 6.9). It has a low-slung of the caudal vertebrae that Hoplitosaurus? is prob- stance with a broad back and hip region. The body ably a specimen of Polacanthus, while J. I. Kirk- of Gastonia was protected by rows of armor plates land, B. B. Britt, and others (1997) and J. I. Kirkland, (scutes) and prominent bony spikes, especially in R. L. Cifelli, and others (1997) consider it to be the shoulder region. In the hip region the dermal Sauropelta. armor scutes were fused into a solid plate that must Some of the confusion over the armored dino- have been impervious to the attacks of early Creta- saurs of the Cedar Mountain Formation began to ceous predators. In addition, the flanks of the body clear in 1998 when James Kirkland described Gas- bore triangular plates that projected outward and tonia burgei on the basis of a reasonably complete continued in reduced form along each side of the partial skeleton found in the Yellow Cat Member tail. It is hard to imagine a better-protected herbi- at the Gaston Quarry (Kirkland 1998b). Thousands vore than Gastonia. of bones belonging to this genus have been recov- The small teeth of Gastonia are confined mostly ered, including several skulls (Carpenter and others to the sides of the jaws; they are reminiscent of The Early Cretaceous 155

Stegosaurus teeth and probably functioned in a similar manner to shear tough, low-growing vegetation. Given its squat stature, heavy armor, and massive limbs, Gastonia was probably a slow-moving and dim-witted creature that needed all the armaments it possessed to survive in a world with many specialized predators. Though Gastonia did not possess a tail club as more advanced and younger ankylosaurs did, most paleontologists consider it to be an early member of that family on the basis of several skeletal similarities. Sauropelta, Polacanthus, and Gastonia are not the only herbivorous dinosaurs in the Yellow Cat fauna. Several types of ornithopod dinosaurs have also 6.10. A fragment of the maxilla with two teeth from been identified in the basal Cedar Mountain fauna. Iguanodon ottingeri. Scale bar = 1 inch (25 mm). Redrawn from Galton and Jensen 1979. Recall that the ornithopods are bipedal herbivores such as Camptosaurus or Dryosaurus of the Morri- son Formation. Traditionally Ornithopoda was con- Member of the Cedar Mountain Formation near sidered a suborder of the order Ornithischia and Moab. Iguanodon ottingeri is based on a single frag- included all of the varied bipedal herbivorous dino- ment of the maxilla (upper jaw) with two teeth pre- saurs. The ornithopods were further subdivided into served (fig. 6.10). As the genus name implies, the several groups of various ranks, including the rela- teeth of Iguanodon are very similar to but much tively primitive hypsilophodonts and iguanodontids larger than the teeth of modern iguanas. The broad and the more specialized hadrosaurs (flat-headed teeth had rounded denticles along the margins “duckbills”) and lambeosaurs (crested “duckbills”). and were no doubt very efficient in shredding veg- Most dinosaur paleontologists today prefer the cla- etation. It is not surprising to find the remains distic approach to classification, so the traditional of Iguanodon in the Cedar Mountain Formation, categories of ornithopods have been redefined or because this genus has also been identified in other abandoned completely. For example, Iguanodon- Early Cretaceous strata of western North Amer- tia is now considered an unranked clade of related ica (South Dakota, after Weishampel and Bjork ornithopods rather than an infraorder or family of 1989). As noted in the preceding chapter, the Morri- the suborder Ornithopoda. While these revisions son Formation has also produced fossils tentatively of the taxonomy may seem arcane and trivial, they identified as the remains of iguanodontid ornitho- have resulted in a more meaningful way of arrang- pods. It should be pointed out that some paleontol- ing the variable ornithopods in groups based on ogists have questioned the identification of a new ancestry rather than on superficial similarities. species of Iguanodon on the basis of such fragmen- While a full review of the cladistics of the ornitho- tary material. D. B. Norman and D. B. Weishampel pod dinosaurs is beyond our scope, those known (1990) list Iguanodon ottingeri as a nomen dubium from the Yellow Cat Member of the Cedar Moun- (doubtful name), while D. B. Weishampel and P. B. tain Formation appear to belong to a basal lineage Bjork (1989) assert that the fossil material is too within the iguanodont group. fragmentary to be diagnostic even at the genus level. Galton and Jensen (1979) reported the occur- More recently discovered fossils from the Yel- rence of Iguanodon ottingeri from the Yellow Cat low Cat Member and Poison Strip Sandstone have 156 Chapter 6

6.11. Recovered skeletal elements (A) and life reconstruction (B) of Iguanacolos- sus fortis from the Yellow Cat Member of the Cedar Mountain Formation. Scale bar = 3 feet (1 m). From McDonald and others 2010. provided clear evidence for the presence and diversity of iguanodont ornithopods in the lower Cedar Mountain Formation. T. DiCroce and K. Carpenter (2001) named and described the distinctive ilium (hip blade), some bones of the hind limb, and other isolated elements of Planicoxa venenica from the Poison Strip Sandstone north of Moab. Planicoxa is a medium-sized ornithopod so similar to Camp- tosaurus of the late Jurassic that some scientists have recognized certain Camptosaurus species as belonging to Planicoxa (Carpenter and Wilson 2008 in chapter 4 references). In addition, later work (Gilpin and others 2007) led to the recognition of a larger, more advanced ornithopod named Cedrorestes on 6.12. Lower tooth (A) and upper tooth (B) of Iguanaco- the basis of part of the pelvis found at the top of the lossus fortis. Scale bar = 0.4 inches (10 mm). From Yellow Cat Member. This ornithopod dinosaur had McDonald and others 2010. a large bony ridge near the hip socket that resembles the more highly specialized “duckbills” (hadro- Hippodraco scutodens (fig. 6.11). Both of these spe- saurs) of the late Cretaceous. Some paleontologists cies are based on fossils that represented a rela- (e.g., Kirkland and Madsen 2007) feel that Cedror- tively large portion of the skeleton. As the name estes and Planicoxa may be large and small versions implies, Iguanacolossus was a large animal, approx- of the same animal. Though some of this confusion imately 30 feet (10 meters) long as an adult. Like remains, it is nonetheless clear that several differ- most iguanodontids, it had hundreds of small leaf- ent types of ornithopods were present in the Yellow shaped teeth (fig. 6.12) in its jaw and probably had a Cat fauna. pronounced thumb spike on its hands, though fore- In 2010 a team of paleontologists led by Andrew foot bones were not preserved with the partial skel- McDonald from the University of Pennsylvania eton that was recovered. Hippodraco, whose name described two large iguanodontid ornithopods from from Greek and Latin roots means “horse dragon,” the Yellow Cat Member: Iguanacolossus fortis and was a somewhat smaller animal, perhaps 15 feet (5 The Early Cretaceous 157

6.13. Recovered skeletal elements (A) and life reconstruction (B) of Hippodraco scutodens from the Yellow Cat Member of the Cedar Mountain Formation. Scale bar = 3 feet (1 m). From McDonald and others 2010.

genera were probably rather subtle, and it might have required careful study of them as living animals to recognize the different genera and species. Ornithopods were a significant part of the Yellow Cat fauna and, as relatively large animals, were no doubt attractive as prey animals to theropods such as Utahraptor and its contemporaries. In addition to the dinosaur genera thus far 6.14. Reconstructed skull of Hippodraco scutodens. Scale bar = 2.5 inches (6 cm). From McDonald and oth- described, the Yellow Cat fauna of the Cedar Moun- ers 2010. tain Formation also included several different sauropods, the best known of which is Cedarosaurus meters) long, though the bones recovered may have weiskopfae (Tidwell and others 2001). Cedarosau- been from a juvenile individual (fig. 6.13). Most of rus is a brachiosaurid sauropod, meaning that it the skull of Hippodraco was preserved along with had slightly longer forelimbs than hind limbs, giv- much of the upper forelimb, pelvis, and spinal col- ing it the giraffelike stance that typified Brachiosau- umn. From this evidence it appears that Hippodraco rus of the late Jurassic (fig. 6.15). Cedarosaurus is has an elongated skull, similar to the basic con- somewhat smaller than its Jurassic ancestor, how- struction of most of the iguanodontid dinosaurs ever, standing about 15 feet (5 meters) high at the (fig. 6.14). The teeth were small and shield-shaped shoulder and with a length of about 50 feet (about (inspiring the species name scutodens) as in sev- 15 meters). The skull of Cedarosaurus is not well eral others iguanodontids. The discovery of Igua- known, but other parts of its skeleton provide addi- nacolossus and Hippodraco in the Cedar Mountain tional indications of its relationship to Brachiosau- Formation, along with the previously known iguan- rus. The Yellow Cat Member has also produced odontids, demonstrates that several different types fragmentary fossils of other types of sauropod dino- of ornithopod herbivores were present in Utah saurs that seem to be more closely related to Cama- when the Yellow Cat Member was deposited around rasaurus (Eberth and others 2006) and Titanosaurus 124 million years ago. The differences between these (Britt and others 1997). Just above the Yellow Cat 158 Chapter 6

6.15. Recovered skeletal elements of Ced- arosaurus weiskopfae from the Yellow Cat Member of the Cedar Mountain Forma- tion. Scale bar = 39 inches (1 m). Based on a photograph from Kirkland and Mad- sen 2007.

Member, in the overlying Poison Strip Sandstone, years reported by B. W. Greenhalgh and others fragmentary skeletal remains of the relatively small (2006) derived from uranium-lead dating of zir- sauropod were discovered in 1998 and soon after con crystals deposited in the lower Cedar Mountain described as Venenosaurus dicrocei by W. D. Tidwell Formation. If the basal Cedar Mountain Forma- and others (2001). In general Venenosaurus was tion is Barremian in age, then the unconformity at similar to Cedarosaurus, though somewhat smaller, the top of the Morrison Formation in eastern Utah reaching an adult length of between 30 and 35 feet encompasses about 20 million years of unrecorded (10–12 meters). Venenosaurus and Cedarosaurus time. What type of dinosaurs, if any, existed during appear to closely related but are clearly two distinct this gap in the rock record may never be known. types of sauropod dinosaurs. More complete fossil material, particularly the bones of the skull, will be The Upper Fauna: The Ruby Ranch needed to assess their relationship in detail. None- and Mussentuchit Assemblages theless, the fossils known thus far from the Yellow Cat Member clearly demonstrate the presence of Above the lowermost beds the Cedar Mountain a varied group of large dinosaur herbivores in the Formation is dominated by fine-grained mudstone lower Cedar Mountain Formation. and shale, containing thin interspersed lenses of The age of the basal fauna of the Cedar Moun- limestone and channel-deposited sandstone. These tain Formation can be estimated at about 125–120 fine-grained sediments of the main body of the for- million years ago on the basis of the overall simi- mation are now known as the Ruby Ranch Mem- larity of the dinosaurs identified in the Yellow Cat ber, which is overlain by the more carbonaceous Member and Poison Strip Sandstone and those that Mussentuchit Member (Kirkland, Cifelli, and others occur in rocks of similar age in Europe. The dino- 1997; fig. 6.5). Fossils of any kind were considered saurs thus far documented in the basal fauna seem rare in these members until the late 1980s. Start- to compare best with assemblages from the Weal- ing with the discovery of the Long Walk Quarry in don Marl of southern England and the Lakota For- Emery County in 1987 (DeCourten 1991), a wave mation of South Dakota (Kirkland 2005; Kirkland, of exciting discoveries was made in the upper por- Cifelli, and others 1997). These two formations are tion of the Cedar Mountain Formation by paleon- thought to be of Barremian age (middle early Creta- tologists from several different institutions. Many ceous), about 125 million years old. This age assess- significant dinosaur fossil sites in these strata have ment is consistent with a date of 126 ± 2.5 million now been located along the Price River and south The Early Cretaceous 159

6.17. A spatulate tooth of a Pleurocoelus-like sauropod from the Long Walk Quarry. Total length of the tooth is about 3 inches.

The Long Walk Quarry is situated in the lower portion of the Ruby Ranch Member. Fossils from this site are dominated by the remains of small sauropods, both adults and juveniles, possibly of the same species (fig. 6.16). The presence of a juvenile specimen is known from dorsal vertebrae that have lost the unfused neural spines (fig. 6.16B) and jaw 6.16. Dorsal vertebra of a adult (A) and juvenile (B) sau- fragments with small teeth, some of which are still ropod from the Long Walk Quarry. These fossils are unerupted from the bone. Though the remains of both very similar to the small sauropod Pleurocoelus. Not the deep lateral pockets (pleurocoels) on both ver- the sauropods from the Long Walk Quarry are frag- tebrae. Scale bars in centimeters. mentary, they bear a strong resemblance to the fossils of Pleurocoelus, a small sauropod previously of Interstate 70 in the San Rafael Swell region, along known from Maryland (Marsh 1888; Lucas 1904), the Colorado River corridor in east-central Utah, Montana (Ostrom 1970), and Texas (Gallup 1974, and in Dinosaur National Monument. So many fos- 1989; Langston 1974). The teeth of the Long Walk sils have surfaced in recent years that it is now very Quarry sauropod (fig. 6.17) are likewise very simi- clear that the upper two members of the Cedar lar to those of Pleurocoelus from the Cloverly For- Mountain Formation yield a dinosaur assemblage mation of Montana (Ostrom 1970) and suggest that that is quite distinct from the Yellow Cat/Poison its diet consisted of leafy vegetation. On the basis Strip fauna that preceded it. The differences between of fossils found in Texas W. Langston (1974) recon- the lower Yellow Cat fauna and the fossil assem- structed Pleurocoelus as a small sauropod about 20 blages from the Ruby Ranch and Mussentuchit feet (6.5 meters) long (fig. 6.18), and it is likely that Members indicate some significant and intriguing the sauropod from the Long Walk Quarry was very changes in the character of Utah’s early Cretaceous similar in appearance and size. The juvenile sau- dinosaur communities. ropod may have been only about 9–12 feet (3–4 160 Chapter 6

6.18. Skeletal reconstruction of the 20-foot-long sauropod Pleurocoelus. Modified from Langston 1974.

6.19. Skull of Abydosaurus seen from the left and right side. Scale bar = 2.5 inches (6 cm). From Chure and others 2010. meters) long and weighed a mere 500 pounds, while fossilization process very well. But four different the adults most likely weighed between 1 and 2 tons. skulls of Abydosaurus were discovered at Dinosaur Exceptionally complete and well-preserved fos- National Monument in a layer of sandstone in the sils of at least four individuals of the same sauro- Mussentuchit Member, one of them almost entirely pod species were recently discovered in the upper complete (fig. 6.19). part of the Cedar Mountain Formation at Dino- Abydosaurus was a sauropod similar to Brachio- saur National Monument (Chure and others 2010). saurus of the late Jurassic and is probably related to Among the fossils recovered was one of the most it. The 18-inch-long (0.5-meter) skull has the high complete sauropod skulls ever discovered, which and enlarged nostrils and short muzzle typical of was used to define the new genus and species Aby- the brachiosaurid sauropods (fig. 6.20). The long dosaurus mcintoshi. In general the skulls of sauro- neck of Abydosaurus may have been as much as 50 pods are very rare because they tend to be lightly feet (about 15 meters) long in adults based on the constructed of thin struts and plates of bones and cervical vertebrae that are preserved along with the are, of course, supported on the end of a very skulls at Dinosaur National Monument. The teeth long neck. Typically, sauropod skulls are quickly of Abydosaurus are a bit more slender than the teeth detached from the neck after death, and the rela- of Brachiosaurus and less flattened than the Pleuro- tively delicate bones do not normally endure the coulus-like teeth from the Long Walk Quarry. Only The Early Cretaceous 161

15–18 feet (5–6 meters) long but was built rather low to the ground, with massive limbs to support the weight of an armored body. Its head, nearly 2 feet (0.6 meter) long, was broad and relatively flat, was tipped with a squarish toothless beak, and included powerful jaws that bore teeth designed to process tough vegetation. Little of the bony armor that probably covered much of the body was preserved with the skeletal remains, so no one can be sure just how well protected from predators Peloroplites was. It is clear, however, that Peloroplites was a massive, slow-moving herbivore that probably fed on 6.20. Reconstruction of the skull and neck vertebrae of tough, low-growing vegetation. In the presence of Abydosaurus. Based on reconstruction by Chure and others 2010. the predators of early Cretaceous Utah such a creature would most likely have carried substantial der- portions of the postcranial skeleton of Abydosaurus mal armor. are known, so it is not yet clear if this early Creta- In addition to Peloroplites, two other species of ceous sauropod had a giraffelike posture like its bra- nodosaurid ankylosaurs are known from the upper chiosaurid relatives and exactly how long the entire Cedar Mountain Formation: Animantarx (Car- body might have been. The four individuals whose penter and others 1999) and Cedarpelta (Carpen- remains are preserved in the Mussentuchit Member ter, Miles, and Cloward 2001). Animantarx was a may be part of an Abydosaurus herd that perished relatively small animal, reaching an average length about 105 million years ago while crossing a stream of some 10 feet (3.3 meters), with a skull (fig. 6.21) bed. Future excavations at the site may reveal many barely a foot long. It was well armored, with rows more details about this new species of early Creta- of keel-shaped bony knobs covering its back and ceous sauropod. prominent spikes protecting its neck and flanks In addition, the upper members of the Cedar (fig. 6.22). Cedarpelta appears to have been a some- Mountain Formation have yielded the remains of what larger nodosaurid, attaining a typical adult many other kinds of dinosaur herbivores. Most body length of 25 feet (8 meters) or more. The skull notable are the fossils that document the pres- of Cedarpelta was about 2 feet (0.6 meter) long and, ence of several taxa belonging to the large family of as in most other nodosaurids, was armored with armored quadrupedal herbivores known as ankylo- numerous plates and small knobs. In addition to saurs. In particular the nodosaurids (a subset of the Peloroplites, Animantarx, and Cedarpelta, other fos- ankylosaurs that lack the famous tail club) are well sils collected from the upper Cedar Mountain For- represented. Collectively the ankylosaurs from the mation appear to belong to one or perhaps several upper portions of the Cedar Mountain Formation other species of armored dinosaurs such as Sau- constitute one of the richest assemblages of armored ropelta (fig. 6.23). The skeletal anatomy of Sauro- dinosaurs in the world (Carpenter and others 2008) pelta is well known from the abundant remains of and include at least three different genera, proba- this nodosaurid found in early Cretaceous strata in bly more. One of the larger of these ankylosaurs is Wyoming and Montana. Sauropelta is a good model Peloroplites cedarimontanus (Carpenter and oth- for the general appearance of the armored dinosaurs ers 2008), whose species name is a reflection of the in the Cedar Mountain Formation, though the fos- formation that preserves its fossils. Peloroplites was sil evidence clearly indicates several variations on 162 Chapter 6 this morphological theme. The armored dinosaurs In addition to the armored dinosaur herbivores known from the Mussentuchit and Ruby Ranch from the upper Cedar Mountain members, at least Members thus suggest a much more diverse assem- one type of relatively advanced ornithopod foraged blage of these creatures than was present in preced- with them in the forests of the early Cretaceous. In ing Yellow Cat fauna. 1992 the remains of a bipedal herbivore were discovered from the same strata near Castle Dale that produced fossils of Animantarx. On the basis of these fossils, James Kirkland later described Eolambia caroljonesa as an advanced ornithopod, possibly related to the hadrosaurs or “duck-billed dinosaurs” of the later Cretaceous (Kirkland 1998a). Additional Eol- ambia fossils, including the remains of several juveniles, have been identified from quarries in the Mussentuchit Member in the southern San Rafael Swell (Garrison and others 2007). Eolambia was a large ornithopod that reached adult lengths of per- 6.21. Reconstructed skull of Animantarx displayed at haps 20–30 feet (7–10 meters) though none of the the College of Eastern Utah Prehistoric Museum. Total length of the skull is slightly less than 1 foot. Photo by juvenile specimens would have been that long (fig. Frank DeCourten. 6.24). This ornithopod had a broad snout, though it was not as well developed as the shovel-snouts of the hadrosaurs that lived in Utah later in the Cre- taceous period. Other skeletal details suggest that Eolambia was somewhat more advanced and specialized than the iguanodontid ornithopods of the lower Cedar Mountain Formation. Though it was for a time considered the earliest hadrosaur or “duckbill,” the most recent analyses of the skeletal features of Eolambia suggest that it was a specialized iguanodontid, a descendant of the more primitive members of this group known from the Yellow Cat 6.22. Skeletal mount of Animantarx at the College of Member and Poison Strip Sandstone (Head 2001). Eastern Utah Prehistoric Museum. Total length of skele- Nonetheless, Eolambia was a large herbivore and ton is approximately 10 feet. Photo by Frank DeCourten.

6.23. Reconstruction of Sauropelta, a 16-foot-long nodosaurid similar in general appearance to the armored dinosaurs known from the Cedar Mountain Formation. Based on Car- penter 1984. The Early Cretaceous 163

6.24. Reconstruction of the skeleton of a juvenile Eolambia caroljonesa from the Mussentuchit Member of the Cedar Mountain Formation. The body length of this juvenile was about 15 feet. Based on Garrison and others 2007.

6.25. Tenontosaurus skeleton based on specimens found in Texas, Oklahoma, and Montana. The total length of skeleton is about 20 feet. Adapted from Langston 1974.

more highly specialized for browsing on leafy vege- Lockley and others 1997). Other herbivorous dino- tation than any of its predecessors. saurs documented on the basis of rather scrappy In addition, it appears that Eolambia was not fossil material from the upper Cedar Mountain the only bipedal herbivore on the scene: teeth and Formation include a small nodosaurid similar to other remains have been recovered from the upper Pawpawsaurus, a primitive ceratopsian or horned Cedar Mountain beds that appear to belong to a dinosaur known only from teeth (Kirkland, Britt, large Iguanodon-like herbivore known as Tenonto- and others 1997; Kirkland, Cirelli, and others 1997; saurus (Kirkland and Madsen 2007). Tenontosau- Kirkland and Madsen 2007), and an unknown small rus was a fairly large Iguanodon-like ornithopod sauropod that shed small isolated teeth more or less 15–20 feet (5–7 meters) long, with a deep and nar- similar to those of Pleurocoelus. row skull that was nearly rectangular when viewed With such a diverse assemblage of herbivorous from the side (fig. 6.25). Tenontosaurus was a slow- dinosaurs in the upper Cedar Mountain Formation, moving browser that probably used a quadrupe- it is no surprise that the remains of several different dal posture when feeding among the low-growing theropod predators are also known. Large curving shrubs, but it could also walk or run bipedally when foot claws (fig. 6.27A) known from several localities necessary. Further evidence of a Tenontosaurus-like demonstrate the presence of dromaeosaurs or “rap- ornithopod in the upper fauna comes from foot- tors.” Dromaeosaur remains from the upper Cedar prints discovered in the Mussentuchit Member in Mountain typically indicate animals much smaller Emery County (fig. 6.26) that have been identified than Utahraptor. These later dromaeosaurids were as “iguanodontid” tracks (Lockley and Hunt 1995; probably much like carnivores such as Deinonychus, 164 Chapter 6

6.27. Theropod remains from the upper Cedar Mountain Formation: A. a claw from the foot of Dei- nonychus, very similar to those from the Ruby 6.26. A large “iguanodontian” footprint from the upper Ranch member; scale bar Cedar Mountain Formation in Emery County. Scale bar = = 2 inches (5 cm); B. large 2 inches (5 cm). Photo by Frank DeCourten. theropod tooth from the upper Cedar Moun- tain Formation as it was a raptor from the roughly contemporaneous Clov- found in the rock matrix; ery Formation of Montana, which was about 12 feet the total tooth length (4 meters) long when full grown. Until more com- nearly 4 inches. plete dromaeosaur material is found, we cannot be sure about which, and how many, small raptors from those of other Cretaceous theropods. The terrorized the herbivores from the upper fauna of appearance of perhaps several different troodon- the Cedar Mountain Formation. In addition, teeth tids in the upper Cedar Mountain fauna is one of from the specialized predators known as troodon- its most characteristic features. Other small thero- tids have been recovered from the upper Cedar pod teeth from the Musserntuchit Member have Mountain Formation. As pointed out in our discus- been referred to as Paronychodon and Richardoes- sion of Koparion from the Morrison Formation, the tesia (Kirkland, Britt, and others 1997), but little is troodontids are of interest because these small pred- known about the skeletons and the overall morphol- ators were probably the most intelligent of all dino- ogy of these teeth-based genera. Collectively the saurs. They were also swift and agile, with excellent small theropod teeth of the upper Cedar Mountain stereoscopic vision. The teeth of troodontids are Fauna suggest a diverse array of petite dinosaur car- very unusual in that the denticles along the cut- nivores, none weighing much more than about 50 ting edge are large with respect to the tooth size and pounds, scurrying through the lush forests in pur- tend to curve toward the tip. The slots between the suit of rodent-sized mammals, lizards, turtles, fish, denticles expand into circular depressions, known eggs and hatchlings, and possibly birds. as blood pits, at the base. These (and other) features It is clear, however, that the raptors and troodon- make it easy to distinguish the teeth of troodontids tids were not the only threat to herbivores: the Ruby The Early Cretaceous 165

Ranch Member has also produced fossil teeth and isolated bones that clearly indicate the presence of much larger and completely different types of theropods (DeCourten 1991; Kirkland and Parrish 1995; fig. 6.27B). Large, bladelike teeth up to 4 inches (10 cm) long, with prominent serrations on the front and back edges, probably came from a fearsome predator perhaps similar to Acrocanthosaurus, known from early Cretaceous deposits in Texas and Oklahoma (Stovall and Langston 1950). Some of the teeth known from the upper Cedar Mountain strata are larger than those of an average Acrocanthosau- rus, however, indicating that the dinosaurs that possessed them may have been as large as Allosaurus of the late Jurassic. Because it is rarely possible to make a precise identification of early Cretaceous theropods from the teeth alone, we can’t be sure exactly what genus and species is represented by these large teeth from the Ruby Ranch Member. We do know, however, that they were big! All of the dromaeosaurs would have been dwarfed by the multiton carnivores that left the huge daggerlike teeth of the upper Cedar Mountain Formation. Some of the nondinosaur fossils from the upper parts of the Cedar Mountain Formation shed addi- 6.28. A fossil quarry in the Mussentuchit Member of tional light on the changes in land and life that the Cedar Mountain Formation in the San Rafael Swell region. The gray carbonaceous mudstones of this occurred during early Cretaceous time in Utah. The quarry have produced a great variety of small fossils. Mussentuchit is the youngest member of the Cedar Photo by Frank DeCourten. Mountain Formation, and much of it is composed of gray carbon-rich mudstones that have produced have revealed the presence of many different types many intriguing fossils. The carbonaceous matter in of conifers, cycads, ferns, and the flowering plants the Mussentuchit Member consists mostly of small (angiosperms). bits of carbonized wood and microscopic masses of The advent of the angiosperms in the early Cre- organic residues. This material, mixed with clay and taceous was a major event in the history of the ter- carbonate minerals in the mudstones, creates a gen- restrial biota because these plants would soon erally darker gray color in the upper beds (fig. 6.28), dominate the global flora, a distinction they hold to as opposed to the pastel purples and lighter grays the modern day. The highly efficient mode of repro- that typify the lower portions of the formation. duction used by the angiosperms, coupled with Accompanying this increase in organic material is the variety of tissues each possesses, created new a rather sudden increase in the abundance of plant food sources for herbivorous animals of all types. fossils of all sizes in the uppermost Cedar Mountain After the early Cretaceous plant-eating vertebrates Formation. Studies of the pollen recovered from the could take advantage of new nutritional resources, Mussentuchit Member (Tschudy and others 1984) such as fruit and flowers, that only the angiosperms 166 Chapter 6

6.29. The winding ribbon of sandstone (middle distance) in the upper Cedar Mountain Formation in Emery County represents an ancient stream channel that became filled with sand and gravel. Such “paleochannels” allow geologists to reconstruct the size, direction, and speed of early Cretaceous streams of central Utah. Photo by Frank DeCourten. produce. The evolution of every group of herbiv- pavement that litters the surface. In places large orous creatures, from the dinosaurs to the insects, trunks of Tempskya are found still in vertical growth was strongly affected by the development of the position: a genuine petrified forest of giant ferns! flowering plants. The dramatic increase in the abundance of plant Even though the angiosperms became estab- fossils suggests that the forested areas were expand- lished in central Utah during the time when the ing and the vegetation was becoming more dense Mussentuchit Member of the Cedar Mountain For- during late Cedar Mountain time. The Mussen- mation was being deposited, they were still small tuchit Member even contains a few thin coal seams and by no means the dominant plants of the time. that indicate profuse vegetation (Tidwell and oth- In Utah the fossils of more primitive coniferous ers 1983). This proliferation of trees and shrubs trees are abundant at many outcrops of the upper may signify a greater supply of water and gener- Cedar Mountain beds (Thayn and others 1983; ally less arid conditions across the central Utah in Thayn and Tidwell 1984). Perhaps the most char- late Cedar Mountain time. Recall that Tempskya acteristic element of the Mussentuchit flora, how- is a fern, albeit an unusually large one, and there- ever, was the giant fern Tempskya (Tidwell and fore probably required a moist and humid habitat. Hebbert 1976). The distinctive dark-colored and Its great abundance in the upper Cedar Mountain fibrous wood of this tree-sized fern is so common Formation is a further indication of damp environ- in the uppermost Cedar Mountain Formation that ments. Such a notable shift in the patterns of climate petrified fragments of it sometimes form a loose The Early Cretaceous 167 and vegetation would be interesting by itself, but the early Cretaceous seas did just that; as the advanc- story has an even more intriguing aspect. ing sea crept ever closer to Utah from the northeast The carbonaceous nature of the sediments in the and south, the rivers began to decelerate in response upper Cedar Mountain Formation seems to sug- to the rising base level. The encroaching sea never gest more sluggish rivers and a more stagnant drain- reached central Utah during the early Cretaceous, age system. If the rivers were flowing swiftly, much but it came close enough to cause a reduction in the of the accumulated plant litter would have been velocity of stream flow (fig. 6.3). With less vigor- washed downstream or would have been decom- ous rivers, less plant litter was flushed downstream posed in the well-oxygenated water of ponds fed by and more organic matter began to accumulate in the the streams. Studies of the ribbons of sandstone left sediments deposited in central Utah. The proximity by rivers (the “paleochannels”) in the upper Cedar of the advancing ocean may also be responsible for Mountain Formation (Harris 1980) suggest low-gra- the increased moisture that is insinuated by the con- dient channels with winding patterns that are typ- spicuous increase in the abundance of plant fossils ical of sluggish streams in the modern world (fig. in the carbonaceous sediments. Coastal regions are 6.29). At first glance, however, the deduction of lan- generally wetter than regions farther inland because guid rivers seems to be at odds with our interpre- the air moving onshore is more heavily laden with tation of wetter climatic conditions. More plentiful moisture evaporated from the surface of the nearby water would seem to increase the velocity of stream- sea. Central Utah was becoming more “coastal” near flow rather than reduce it. The resolution of this the end of early Cretaceous time as the sea advanced interesting paradox involves an oceanic event that to the west from the interior lowland of North was occurring on a global scale near the end of the America. early Cretaceous. Very good geological evidence Thus by the time the sediments of the Mussen- indicates that at this time sea level began to rise tuchit Member were deposited it appears that the everywhere on earth. This was just the beginning landscape of central Utah had experienced a sig- of a process that would continue in even more dra- nificant change. Water was more plentiful in the matic fashion into the Late Cretaceous. As sea level swampy lowland, and plant growth was much more rose, the ancient Gulf of Mexico crept north into luxuriant than had been the case on the semi- central North America while the ancestral Arctic arid plains during the earlier stages of the Creta- ocean penetrated south, submerging the lowlands ceous. Optimal dinosaur habitats developed under of modern Manitoba and Saskatchewan. Eventually these “improved” conditions. This verdant terrain these two encroaching arms of the sea would meet also sustained large populations of other terres- to form the Western Interior Seaway of the Late trial and semiaquatic vertebrates. A rich assemblage Cretaceous, splitting North America into two island of lizards, semiaquatic reptiles such as croco- continents. diles and turtles, amphibians, and several differ- Near the end of the early Cretaceous this oceanic ent types of primitive mammals is documented advance or transgression was just beginning. One by small fossils found in the Mussentuchit Mem- way to slow a river down is to raise its base level, ber. The Mussentuchit mammals are a very inter- the elevation of its mouth. The ultimate base level esting assemblage (fig. 6.30), including the world’s for nearly all the world’s rivers is sea level. If the oldest marsupial (Cifelli 1993; Kirkland and Mad- seas rise, then the ultimate base level rises as well. sen 2007). The nondinosaur reptiles are dominated This in turn decreases the elevation drop between by semiaquatic crocodiles and turtles (Nelson and the headwaters and the mouth of the river, causing Crooks 1987) that thrived in the numerous streams it to flow with less energy. The transgression of the and ponds in the swampy forests. Amphibians 168 Chapter 6

in the upper Cedar Mountain Formation (Jensen 1970). Some of these shell fragments may be from dinosaur nests, but we can only speculate about what creatures laid the eggs until someone finds an embryo preserved inside—and there are many good candidates in the upper Cedar Mountain fauna. Imagine what central Utah must have been like around 100 million years ago when the upper layers of the Cedar Mountain were deposited. Herds of several different types of ornithopods ambled slowly through the undergrowth of the shadowy wood- lands, grazing on the leaves of ferns, angiosperms, and other types of plants. They would occasionally have passed low-browsing armored nodosaurs in the underbrush, who probably took little notice of their presence. Meanwhile the leafy vegetation of the higher forest canopy was nipped by migrant sauropods moving across the landscape in rhythm with the seasons. Packs of stealthy raptors were a constant threat to the herbivorous dinosaurs and probably congregated along migration routes or bodies of water, awaiting unwary prey. Large menacing theropods, fewer in number than the raptors, would move about as solitary individuals or in small groups, waiting for the opportunity to subdue 6.30. Mammal fossils from the upper Cedar Mountain weak, isolated, or incapacitated sauropods and orni- Formation of Utah: A. a jaw fragment from Kokopelia thopods. The insects, reveling in the arrival of the juddi, the world’s oldest marsupial; B. a multituberculate angiosperms, would have buzzed through the heavy tooth; C. a mammal tooth with three cusps. Scale bar = 0.04 inch (1 mm) in all sketches. A: redrawn from Cife- moist air searching for nectar among the world’s lli 1993; B: based on photograph by Eaton and Nelson earliest flowers. The swampy thickets would liter- 1991; C: adapted from Nelson and Crooks 1987. ally have fluttered with the movement of smaller creatures such as lizards and birds, while primitive such as salamanders were plentiful (Gardner 1995); crocodiles cruised the streams crossing the region. because they cannot survive or reproduce outside Much of central Utah during the time represented of moist habitats, they provide further evidence of by the upper Cedar Mountain Formation proba- marshy conditions in the uppermost Cedar Moun- bly looked, sounded, and felt a bit like the modern tain Formation. A diverse assemblage of lizards also Everglades of Florida. prowled through the undergrowth of the lush Cedar Periodically, under the erratic climate of the early Mountain forests, including a large active preda- Cretaceous, droughts would sweep across the land- tor that was probably close to 3 feet (1 meter) long scape. The rivers would wither, and the lush forests (Cifelli and Nydam 1995; Nydam 1995). With so would turn brown. Plant-eaters of all types would be many egg-laying reptiles around, it is little wonder attracted to the dwindling bodies of water; in their that many eggshell fragments have also been found weakened condition, they became easy targets for The Early Cretaceous 169 predators. Even if they avoided the raptors and large theropods, the dry conditions limited the growth of their food. Death by starvation was always a threat during prolonged droughts. In such instances the skeletons of several individuals from a herd might be preserved as fossils in close proximity to each other. At other times, during wet climate cycles or as hurricanes and tropical storms moved inland, the seawater was too abundant. Floods may have raged across the region, transporting sand, gravel, and mud that would eventually settle out as layers of sediment in the lowlands. As the interlaced rivers rose and breached their banks, many dinosaurs and other creatures were swept to their death, their remains concentrated where the floodwaters ponded. The result would have been the several bone beds in the upper Cedar Mountain Formation that produce the disarticulated fossils of many different kinds of animals.

The Early Cretaceous Faunal Transition

While all the repetitive cycles in seasons, climate, 6.31. Global geography during the life, and death were transpiring across the central time when the Utah landscape, changes in global geography were members of the underway in the early Cretaceous that had profound Cedar Mountain influences on North American dinosaur faunas. Formation were deposited in cen- As we have seen, the dinosaur assemblages known tral Utah. Modi- from the upper and lower portions of the Cedar fied from Kirkland Mountain Formation are notably different. These 2005. differences are summarized in figure 6.5. The lower Yellow Cat Member and Poison Strip Mountain dinosaur fauna has improved over the Sandstone produce an assemblage dominated by a past two decades, paleontologists have noted an diverse array of large and relatively primitive orni- overall similarity between this array and early Cre- thopods (such as Planicoxa and Iguanodocolossus), taceous dinosaur communities that lived in Europe a few nodosaurs (Gastonia), large raptors (Utahrap- at the same time (Kirkland, Carpenter, and oth- tor), some small predators (Nedcolbertia), therizi- ers 1998; Carpenter and others 2002; Kirkland and nosaurs (Falcarius), and several different types of Madsen 2007). Reconstructions of global paleo- sauropods (Cedarosaurus, Venenosaurus). Not all of geography (fig. 6.31) suggest that North America these dinosaurs lived at exactly the same time, but and Europe were joined at this time, allowing free collectively they demonstrate the overall charac- migration of dinosaurs between the two continents. ter of Utah’s dinosaur communities about 120 mil- This faunal interchange may be the basis for the lion years ago. As our knowledge of the lower Cedar 170 Chapter 6 similarity between North American and European Sandstone rests on the Cedar Mountain Formation dinosaur fauna. above a prominent unconformity, indicating a brief By the time the upper members of the Cedar period of erosion after the deposition of the sed- Mountain Formation were deposited around 100 iments producing the upper dinosaur fauna. The million years ago, North America had become lower and middle horizons of the Dakota Formation largely separated from Europe by the opening of the have yielded the remains of small terrestrial and north Atlantic Ocean basin. At about this same time aquatic vertebrate such as mammals, fish, croco- a land connection was established between Asia and diles, turtles, and dinosaurs (Eaton 1993). The sparse North America in the region surrounding modern dinosaur fossils from the Dakota Formation have Alaska and Siberia (fig. 6.31). The dinosaur fauna not been studied in detail, so little is known about from the upper members of the Cedar Mountain the nature of the dinosaur communities that they Formation reflects this change in global geography. represent. These animals evidently lived in an envi- The exceptionally diverse array consists of quadru- ronment much like the one in which the uppermost pedal armored nodosaurids such as Cedarpelta and Cedar Mountain sediments accumulated. The upper Animantarx, several kinds large sauropods such as layers of the Dakota Formation, however, yield a Abydosaurus and Pleurocoelus, a unique array of completely different assemblage of fossils, domi- ornithopods including Eolambia and Tenontosaurus, nated by marine molluscs such as oysters and clams large predators similar to Acrocanthosaurus, smaller (am Ende 1991; Eaton 1993). From this evidence it is predatory raptors, and at least a half-dozen differ- clear that the Dakota Formation records the steady ent kinds of small furry mammals. The overall char- incursion of the sea into south-central Utah from acter of this assemblage is similar to coeval dinosaur the east. The transgression of the Western Interior communities known from Asia (Kirkland 1996; Seaway into central Utah following the deposition Kirkland and Madsen 2007). Thus it appears that of the Cedar Mountain Formation submerged most migration of dinosaurs from different continents of the dinosaur habitat that was formerly occupied may have played a significant role in the evolution by the creatures of the Cedar Mountain faunas. This of Utah’s dinosaur communities between about 125 mid-Cretaceous transgression is part of the Green- million years ago and about 100 million years ago. horn Cycle, the earliest and greatest of several epi- The difference between the upper and lower fau- sodes of oceanic inundation that affected the Rocky nas known from the Cedar Mountain Formation Mountain region in the late Cretaceous (Weimer may also reflect changes in climate, landscape, and 1983). The Greenhorn transgression ultimately flora that occurred during this same interval. Pale- resulted in a linear seaway that extended from ontologists continue to study this important transi- northern Canada to the ancestral Gulf of Mexico, a tion because (as we will see in the next chapter) the distance of almost 6,000 miles. The Greenhorn sea- dinosaurs that arrived in Utah during the early Cre- way was about 1,000 miles wide, stretching from the taceous were the earliest immigrants of lineages that foothills of the Sevier Orogenic Belt in western Utah would come to dominate North American faunas in as far east as Kansas and Iowa. later portions of the Cretaceous period. The development of the great Western Inte- rior Seaway, initiated during the Greenhorn Cycle, The Dakota Formation ended the Early Cretaceous chapter of dinosaur his- In east-central Utah the Cedar Mountain For- tory in Utah by eliminating much of the prime hab- mation is capped by the Dakota Sandstone, a thin itat that these reptiles required. The dinosaurs that sequence of pebbly conglomerate, sandstone, lived in Utah as the Greenhorn sea advanced either shale, and siltstone. In most locations the Dakota migrated to other areas beyond the region that were The Early Cretaceous 171 less affected by the encroachment or withdrew to a narrow strip of land between the Sevier Orogenic higher terrain in the Sevier Orogenic Belt, where Belt and the receding shoreline. The dinosaurs even- their remains were not preserved. However effective tually returned to this low coastal plain. When they the Greenhorn transgression was in clearing Utah did, the array of Late Cretaceous dinosaurs was of dinosaurs, it was a temporary event. After about strikingly different from any of the faunas that had 90 million years ago, in Late Cretaceous time, the preceded them—yet another fascinating twist in the seas withdrew a short distance to the east, exposing story of land and life in Mesozoic Utah. Chapter 7 The Late Cretaceous 07The Beasts of the Bayous Utah State Highway 10, extending south from Price friction after they have absorbed water. When trav- to I-70, follows Castle Valley, a low strip of land eling along the dirt roads of Castle Valley, it’s wise between the eastern escarpment of the Wasatch Pla- to keep one eye trained on the weather. A surprise teau on the west and the rolling incline of the San rain shower can quickly turn a dusty road to a quag- Rafael Swell rising to the east. The highway rises mire of sticky mud. If you should become stranded and falls gently as it passes through Huntington, in this manner in Castle Valley someday, the best Castle Dale, Ferron, Emery, and the barren low- way to kill time while you’re waiting for the mud to lands that separate the towns. The land along the dry out is to crack open the hard nodules of lime- shoulders of the highway is a bleak expanse of gray stone that occur more or less randomly in the shale. soil, mantled here and there by a white mineral Chances are very good that you’ll find a fossil of a crust that supports only a sparse cover of vegeta- Late Cretaceous ammonite or a clamlike bivalve in tion (fig. 7.1). Farming doesn’t pay very well in Cas- the nodule (fig. 7.2). Such molluscan creatures were tle Valley, except where the streams falling from the very common inhabitants of the Late Cretaceous mountainous plateau have washed better soil over sea in Utah, and you’ve become mired in the muddy the infertile gray dirt. The massive blue-gray shale sediment that accumulated on its floor in Castle exposed in the low roadcuts along the highway, cou- Valley. These ancient sea-floor deposits are known pled with lack of moisture in this desert region, is as the Mancos Shale. to blame for the failure of productive agriculture here. This shale is composed mostly of clay, heav- The Mancos Sea ily mineralized with alkaline salts. The minerals are drawn upward from the shale by water evaporat- The Mancos Shale is an extremely thick and wide- ing at the surface to leave the thin white crusts that spread accumulation of mostly fine-grained marine mottle the gray hummocks. Some of the minerals in sediments. In the Castle Valley region it is over the shale, most notably selenium, have toxic effects 5,000 feet thick and includes many subdivisions on most plants and serve to enhance the sterility of or members. Along the eastern escarpment of the the soil. Few grasses or shrubs can tolerate such a Wasatch Plateau the thick Mancos Shale forms a noxious soil chemistry, even if they could withstand smooth slope that rises upward from the floor of the aridity. The clay in the “blue mud” has another Castle Valley to meet the ragged vertical cliffs hun- interesting property: it swells whenever water is dreds of feet above. A similar slope is formed by applied to it. When wet, the clay becomes imper- the Mancos Shale at the base of the Book Cliffs, meable: any additional water will flow over the sur- which extend east from Price. This enormous mass face rather than seeping in. As the clay expands in of Late Cretaceous mud and silt extends eastward the rain, the gray soils of Castle Valley can become into western Colorado, where the name for such unbelievably slick. This is because the sheetlike clay outcrops originated in the vicinity of the small molecules can slide on one another with virtually no town of Mancos. To the south, in the area around

172 The Late Cretaceous 173

7.1. The Mancos Shale (lower gray slopes) and the Mesaverde Group (upper cliffs) exposed along the east side of the Wasatch Plateau in the Castle Valley area. Courtesy John Telford.

Bryce Canyon, similar offshore marine deposits are known as the Tropic Shale. Siltstone and shale very similar to the Mancos Shale extends north to Wyo- ming, where it is known variously as the Aspen, Mowry, and Hilliard Shale (along with other formations between them). In fact deposits like the Mancos Shale accumulated over the entire area flooded by the Greenhorn and other transgressions of the Late Cretaceous, from Canada to Mexico. All of these formations represent offshore, relatively deep-water marine environments (fig. 7.5). Collec- 7.2. Pycnodonte newberryi, an oysterlike bivalve (left), tively they document over 20 million years of oce- and Scaphites (right), an ammonite cephalopod from the Mancos Shale of Utah. These fossil molluscs are anic submersion in western North America. typical of the invertebrates that lived in the open marine Because dinosaurs were strictly terrestrial ani- environment of central Utah during the late Cretaceous. mals, the Mancos Shale and the other late Cretaceous Scale bar = 1 inch (25 mm). 174 Chapter 7

7.3. Pliosaurs were predatory marine reptiles with relatively short necks and elongated heads. The pliosaurs known from the Mancos Shale and Tropic Shale of Utah were 20–35 feet long as adults. offshore marine deposits of Utah have not produced many dinosaur fossils. In addition to the abundant invertebrate fossils that they contain, however, these sea-floor sediments occasionally yield the remains of sharks, fish, and marine reptiles. Very rarely the bones of animals that died near the shore are also preserved in the Mancos Shale, presumably as a consequence of their carcasses drifting offshore after death. Among the fossils of marine reptiles, those of 7.4. Paddlelike the plesiosaurs are the most abundant in the Man- hind limbs of cos Shale and its equivalents in western North Amer- Utah’s Cretaceous ica. The plesiosaurs were large (up to 40 or 50 feet pliosaurs: Eopoly- cotylus (left) and [13–17 meters] long) seagoing reptiles with paddle- Palmulasaurus like appendages and serpentine necks. The legendary (right). Scale bar Loch Ness monster, though it is a completely mythi- = 2 inches (5 cm). cal beast, was inspired by the plesiosaurs, the real sea Based on Albright and others 2007. monsters of the Mesozoic. Plesiosaur remains have been found in the open marine deposits of the Man- cos Shale and its equivalents across western North that helped to stabilize them in water and allowed America, including Wyoming, Colorado, and New some maneuverability as they pursued prey. The Mexico (Wells 1952; Breithaupt 1985; Lucas and oth- narrow jaws were lined with many sharp, conical ers 1988). teeth. The pliosaurs probably preyed primarily on In the Utah region relatively short-necked plesio- fish and ammonites, both of which were abundant saurs, known as pliosaurs, are known from remains in the Mancos-Tropic sea. recovered from the Mancos Shale (Carter 1991) and In addition to the plesiosaurs, the Late Creta- in the Tropic Shale of southern Utah (Albright and ceous seas of North America also contained turtles, others 2007). Fossils representing at least four dif- sharks, huge marine lizards known as mosasaurs, ferent types of pliosaurs have been found in the and crocodilians (Nicholls and Russell 1990). Shark Tropic Shale, including Brachauchenia, Palmulasau- teeth and fish fossils can sometimes be found locally rus, and Eopolycotylus (Albright and others 2007). in Utah exposures of the Mancos and related sed- The pliosaurs (fig. 7.3) were excellent swimmers, iments (e.g., Stewart and others 1994), such as the with a compact and streamlined body, primarily Mowry Shale and the Tropic Shale. Due to the close propelled by a powerful tail. The limbs of pliosaurs proximity of the western edge of the great inland were modified into paddlelike appendages (fig. 7.4) sea to the mountainous Sevier Orogenic Belt (fig. The Late Cretaceous 175

7.6. Ichthyornis, a ternlike shorebird about 8 inches high known from the Mancos Shale.

7.5. The Mancos-Tropic sea of Utah was part of a larger terrain immediately west of the central Utah shore- seaway that submerged much of central and western North America during the late Cretaceous period. line. Good geological and paleontological evidence Reconstruction from Ronald Blakey/Colorado Plateau indicates that the environmental conditions (such Geosystems, Inc. Used with permission. as turbidity, temperature, and salinity) in this large seaway were anything but uniform (Kauffman 1977), 7.5), the influx of sediment was much greater in the giving rise to distinctive and endemic fauna in dif- Utah portion of the seaway than it was farther off- ferent parts of the ocean basin. shore. The water that covered eastern Utah during Even though the fossil assemblage from the Man- the Late Cretaceous was probably muddy and tur- cos Shale and Tropic Shale is dominated by marine bid, as tiny silt grains, suspended in the water col- creatures, the remains of terrestrial animals are umn, sank very slowly toward the bottom. Thus occasionally encountered. Such fossils provide some the fauna of marine reptiles in Utah was proba- clues about the life that populated the shore of the bly well adapted to the local nearshore conditions Mancos-Tropic sea. We know that seabirds inhab- that prevailed in the region. Farther east, in Kansas ited the edges of the Mancos seashore, but they were and Colorado, a different array of mosasaurs, fish, different from the avian fauna of today. S. G. Lucas and turtles populated the shallow, clear water that and R. M. Sullivan (1982) discovered the partial existed in that part of the seaway. Because the sea remains of Ichthyornis in the Mancos Shale of north- covered literally millions of square miles and had western New Mexico, not far from Utah. Ichthyornis an enormous north-south reach, climatic factors was a small bird, only about 8 inches (20 centime- may also have controlled the distribution of ver- ters) high, and appears to have been a strong flier tebrates in the Western Interior Seaway. The shal- by virtue of its expanded sternum, L-shaped ribs, low water of the Mancos Seaway in Utah might have and modified fingers (fig. 7.6). In these features Ich- been slightly fresher (lower in salinity) than the thyornis closely resembles the modern gulls and water farther offshore. This is due to the high rate terns that are capable of flying great distances over of freshwater runoff from the elevated mountainous land and water in coastal regions. Unlike its avian 7.7. Ichthyornis feeding along the beach of the late Cretaceous Mancos sea. Illustration by Carel Brest van Kempen. The Late Cretaceous 177 descendants, though, Ichthyornis had many small of the nasal chamber. Almost certainly more than and sharply pointed teeth lining its elongated jaws. a single hadrosaur roamed along the edges of the Because the remains of Ichthyornis throughout the Mancos sea in the Utah region, because the low West are found in marine deposits (the best spec- coastal plain was covered by dense jungles that imens occur in Kansas), it is regarded as a seabird could have supported many such herbivores (see the that inhabited the margins of the Western Interior discussion later in this chapter). Their remains are Seaway, feeding on fish and other marine organ- usually preserved in the sediment deposited on the isms that it captured on flights over the water. Other adjacent coastal plain, however, not in muck that birds known from the strata that accumulated in accumulated on the floor of the open ocean. The this seaway include Hesperornis, a large loonlike Colorado locality probably represents a rare event diving bird, and Baptornis, its smaller relative. in which a hadrosaur carcass was washed out to sea, While most of what we know about the birds of eventually sinking to the bottom to become buried the Mancos sea is based on fossils found in the cen- under Mancos mud. Such events would have been ter or eastern parts of the basin, it is plausible to uncommon, because the rivers that flushed this car- imagine that the Utah shores were populated by cass offshore would normally accelerate its destruc- great numbers of shorebirds (fig. 7.7). If we could tion by rolling and tumbling the putrefying corpse. have strolled along the beaches of central Utah in Even if the body or a part of it reached the sea, the the late Cretaceous, we probably would have noticed sharks, predaceous fish, plesiosaurs, and mosasaurs great flocks of reptilelike birds soaring overhead of the Mancos were voracious carnivores. It would and bobbing in the surf. Occasionally a pterosaur not have taken these meat-eaters long to find the might have drifted by as well. Pterosaur remains remains and consume them. are plentiful in the ooze deposited in Kansas at the One of the most remarkable fossil specimens same time when parts of the Mancos Shale were laid known from the Mancos-Tropic Shale interval was down. Though no well-preserved pterosaur fossils discovered by Merle Graffam in 2000 during the are known from the Mancos Shale, at least some of excavation of a large plesiosaur skeleton near Big them probably lived along the western fringe of the Water, Utah. Scientists from the Museum of North- seaway. The “bird”-watching would have been great ern Arizona eventually recovered an amazingly in Late Cretaceous Utah, but our feathered friends complete (fig. 7.8), though mostly crushed, skele- would have had a distinctly reptilian look. ton of a primitive theropod dinosaur that was later Very rarely the Mancos Shale affords a glimpse named Nothronychus graffami (Gillette 2007; Zanno of the larger creatures that lived along the coastal and others 2009). The remains of this therizino- plain near the shore. In western Colorado amaz- saur somehow survived the scavenging marine rep- ingly complete remains of a hadrosaur have been tiles and processes of postmortem decomposition found in the concretions like those that often pro- to arrive more or less intact on the seafloor some duce ammonite and bivalve fossils (Wolny and oth- 50 miles from the nearest land. It was buried in the ers 1990). The hadrosaurs, as we will see later in murky depths of the ocean in mud that later hard- this chapter, were highly specialized bipedal dino- ened into the Tropic Shale. Nothronychus was an saurs (the “duckbills”) that were extremely success- odd animal, much larger than its relative Falcarius ful almost everywhere in North America during the known from the Cedar Mountain Formation, with late Cretaceous. The hadrosaur discovered in the large sicklelike claws on its hands (fig. 7.9). These Mancos Shale of western Colorado appears to be claws are reminiscent of the slashing sabers on the most similar to Kritosaurus, a duckbill with a prom- feet of the raptors but were carried on the hands inent bump on its nose formed by the expansion and probably used for acquiring and handling food. 178 Chapter 7

7.8. Skeleton of Nothronychus graffami from the Tropic Shale of southern Utah. Scale bar = 1 foot (30 cm). Based on reconstruction by V. O. Leshyk in Zanno and others 2009.

7.9. Sketch of the manus (hand) of Nothronychus graffami. Scale bar = 4 inches (10 cm).

In life Nothronychus must have had an ungainly, neck bearing a small skull. Paleontologists are not almost comical appearance. It stood about 12 feet certain if Nothronychus was a strict herbivore or (4 meters) tall on its stout hind legs but appears to was omnivorous, consuming animal remains occa- have held the 20-foot-long (7-meter) body in a more sionally. In either case, though, it lacks the extreme upright bipedal stance than other theropods. The specializations for meat-eating that typify its rela- deep abdominal cavity gave it a pot-bellied look, tives within the theropod clade. It is easy to imagine and the short tail and heavy legs suggest a waddling Nothronychus waddling through the coastal jungles sort of movement rather than the swift and grace- of central Utah 90 million years ago, pulling down ful running styles of other bipedal dinosaurs. A long branches of trees with its large claws to reach the neck and small head added another gawky aspect foliage, fruit, seeds, or cones. Nothronychus was one to this 1-ton reptilian troll. The name Nothronychus of the earliest theropods in Utah to develop adap- means “sloth-claw,” and indeed this strange dino- tations for plant-eating and in many ways was an saur may have been the Cretaceous equivalent of the evolutionary pioneer: the omnivorous theropods slow-moving sloths of the modern world. become much more common a few million years In fact there is likely another similarity between later toward the end of the Cretaceous. Nothronychus and modern sloths: they probably had similar dietary preferences. In a fascinating evolu- The Mountains Tremble: tionary transformation, Nothronychus appears to The Main Phase of the Sevier Orogeny have been mostly herbivorous, even though it is classified as a theropod dinosaur, a group other- As the waters of the Mancos Sea lapped quietly wise consisting exclusively of predators. Evidence against the shore in central Utah, the mountains ris- of plant-eating in Nothronychus includes the prob- ing to the west were rumbling with intensified geo- able toothless beak (presumed because the skull is logical activity. In the late Cretaceous the main unknown but nonetheless likely based on similarity phase of the Sevier Orogeny occurred, an event to other therizinosaurs), a pelvis designed to accom- that brought dramatic changes to the mountain- modate a large digestive mass, and a long flexible ous terrain of western Utah and eastern Nevada. The Late Cretaceous 179

The effects of the Sevier Orogeny are well displayed in a north-south trending belt that extends from the Mojave Desert region of southeastern Cali- fornia, through southeastern Nevada and western Utah, all the way to the area around Yellowstone National Park in Wyoming. Throughout this region, known as the Sevier Orogenic Belt, the earth’s crust was intensely deformed several times during the late Cretaceous as compressive forces crumpled and splintered rocks of pre-Cretaceous age. This great geological disturbance was named for the Sevier Desert of Utah, where its effects are particularly striking (Armstrong 1968). Elsewhere along the belt in Utah tortured rock strata that yielded to the powerful geological forces of the Sevier Orog- eny are exposed in the Wasatch Mountains (Bruhn and others 1983; Yonkee 1992), northwest Utah (Jor- dan 1981), central Utah (Lawton 1985), and the Bear River Range–Crawford Mountains region in the extreme northeast corner of the state (Royse and 7.10. Paleogeography of the Utah area about 70 mil- others 1975). lion years ago. Mountainous terrain in the western part of the state is the Sevier Orogenic Belt. Reconstruction All along the Sevier Orogenic Belt pre-Creta- from Ronald Blakey/Colorado Plateau Geosystems, Inc. ceous rocks were subjected to extreme compres- Used with permission. sion during the late Cretaceous. As we have seen, the deformation probably began on a much smaller western Utah and eastern Nevada; but as the slabs scale as early as late Jurassic time. But in the late above them were driven to the east, they eventu- Cretaceous great folds formed in the rock strata as ally met the crustal buttress in central Utah. Here, the squeezing forces became amplified. The folds along the trend of the present-day Wasatch Moun- piled higher and higher upon one another, much tains, the slabs of contorted rock piled up like shin- as a small rug would behave if you slid it across a gles on a roof. As the great thrust sheets were forced slick floor, jamming it against a wall. The “back- over each other, and as the rocks in each slab were stop” for the east-sliding slabs of rock was evi- bent and crumpled, the land surface rose higher and dently the ancient edge of thick continental crust, higher. In time a majestic mountain range devel- mostly Precambrian in age, that runs almost north- oped in central Utah, with peaks reaching an eleva- south through central Utah (Pilcha 1986). At times tion of 15,000–20,000 feet and slopes that extended the compressive forces also produced enormous from Emery County to eastern Nevada. This ele- low-angle fractures that allowed slabs of rock to vated terrain has been referred to as Laramidia move over each other like playing cards in a deck. (Sampson, Gates, and others 2010) and developed as These nearly horizontal fractures, referred to as a consequence of the geologic disturbances defining thrust faults (or simply “thrusts”), further compli- the Sevier Orogenic Belt (fig. 7.10). cate the already bewildering pattern of folding seen The source of the compression that fueled the in the rocks affected by the Sevier Orogeny. The Sevier Orogeny was the convergence of tectonic thrusts originated several miles below the surface in plates along the western edge of North America, 180 Chapter 7 situated in central California during the late Cre- from the west to form the ragged peaks of Lar- taceous. As the North American plate was forced amidia, Utah’s most magnificent Mesozoic moun- to the west over sinking oceanic plates, compres- tain system. sion was transmitted inland, where it wrought the geological havoc so obvious in the pre-Cretaceous The Sevier Foreland Basin: rocks of central Utah. But the deformation in the Home of Utah’s Late Cretaceous Dinosaurs Sevier Orogenic Belt was not a continuous process throughout the Late Cretaceous. At least four The Sevier Orogenic Belt is a classic example of a pulses of deformation affected the crust of west- fold-thrust belt, the type of mountain system that ern and central Utah from about 90 million years evolves whenever the compressive forces gener- ago to about 60 million years ago (DeCelles and ated by plate convergence are sufficiently power- Mitra 1995). These episodes of deformation in the ful and long-lived. The ascent of the Sevier belt in Sevier belt may have been the consequence of peri- the late Cretaceous steepened the gradient of rivers odic changes in the rate of convergence of the plates, draining the elevated land and initiated vigorous the thickness of the plates, the angle of convergence, erosion of the rising land. Even though the Sevier and the friction between the subducting oceanic system rose faster than it was being worn down, a plates and the overriding North American plate. We prodigious amount of sediment was shed from its do know that the subduction along the west edge of core during each pulse of uplift. The sediment was North America during the Mesozoic was not a con- washed through the rugged canyons and flushed out tinuous and uniform process but occurred in several onto the lower land adjacent to the mountain front. spurts and cycles (Ward 1995). It seems plausible In the low ground of south-central Utah, immedi- that the cyclicity in the subduction process might be ately east of the Sevier Orogenic Belt, thick layers of responsible for the episodic nature of Sevier defor- sand, gravel, and mud piled up. The low area adja- mation, but this concept has not yet been verified. cent to a developing fold-thrust belt that receives In any case the rise of Laramidia in western Utah the erosional refuse from it is known as the fore- was clearly a sequential event. A period of rapid land basin. The Sevier foreland basin was an elon- uplift via folding and faulting would elevate the land gated trough that extended in a southwest-northeast for a few million years, followed by a period of qui- direction through central Utah, parallel to and just escence. Later the compressive forces were intensi- east of the mountain system to which it was linked. fied again: earthquakes would shake the region once During each pulse of uplift in the Sevier belt, a flood more as the mountains heaved skyward. During the of debris spread out to the east, forcing the Western brief lulls between the stages of active uplift, ero- Interior (Mancos) Sea back toward Colorado. The sion would reduce the elevation of the mountains wedge-shaped masses of sediment that were depos- slightly as sediment was shed into the lower terrain ited in response to the episodic uplift gradually built to the east. But whatever elevation was lost during up a gently sloping coastal plain between the peaks the erosional interludes would be reclaimed as soon to the west and the open sea to the east (fig. 7.10). as the powerful compressional forces returned to lift As each pulse of folding and thrusting in the the peaks to even loftier heights. When the Sevier Sevier Orogenic Belt lifted the mountains higher, Orogeny finally ended in the eastern Great Basin additional sediment was shed into the foreland region, near the close of the Cretaceous, the earth’s basin, adding weight to the surface of coastal low- crust had been shortened by about 60 miles through lands. In response to the increased sediment load the combination of the folding and thrusting. An produced by the combination of uplift and erosion immense amount of rock had been transported in the Sevier Orogenic Belt, the western edge of the The Late Cretaceous 181

7.11. Late Cretaceous sediments of the foreland basin in central Utah. Cycles of uplift in the Sevier Oro- genic Belt and subsidence in the foreland basin produced a complex interfingering of marine and terrestrial deposits. Late Cretaceous strata are thickest near the mountain belt and thin noticeably to the east, where the foreland basin subsided less. foreland basin in Utah would periodically subside as the earth’s crust sunk under the weight of the additional geological litter. Farther east from the Sevier belt, in the middle of the Western Interior Seaway, less subsidence took place in the foreland basin because there was less loading of the earth’s crust through deformation and sediment accumulation. As the western edge of the foreland basin subsided, eventually the sea crept back to the west over the sinking land, sometimes reaching as far as the foothills of the Sevier range. For at least the last 30 mil- 7.12. Synorogenic conglomerate in Spanish Fork Can- lion years of the Cretaceous, this back-and-forth yon represents rock rubble shed east from the late battle between land and sea persisted. Several east- Cretaceous Sevier Orogenic Belt. Photo by Frank ward withdrawals (regressions) of the Western Inte- DeCourten. rior Seaway were followed by westward advances (transgressions). The regressions were linked to the the sea invading from the east. The record of these cycles of uplift, while the transgressions peaked at events is a thick and complex sequence of Late Cre- times of geological tranquillity in the Sevier Oro- taceous sediments that accumulated along the west- genic Belt. ern edge of the foreland basin (fig. 7.11). Each period The coastal plain, that strip of nearly flat land of uplift in the mountains generated a great pile between the rugged slopes of the Sevier belt and of gravelly rubble that was transported by streams the open ocean, varied in width in rhythm with the down the eastern slopes of the Sevier belt. These cycles of transgression and regression. At times of gravelly deposits are known as synorogenic con- peak regression (following a pulse of uplift) it was glomerates (fig. 7.12) because their deposition is several hundred miles wide. During transgressions linked to episodes of mountain-building (techni- much of the coastal plain was submerged by the cally known as an orogeny) to the west. Farther east advancing sea. In some places, at certain times, it these coarse sediments grade into thinner tongues may have been as narrow as only a few miles. Thus of finer-grained sandstone and mudstone depos- the Late Cretaceous coastal plain of central Utah ited by rivers on the coastal plains. Along the west- was constantly changing. It was alternately buried ern edge of the Western Interior (Mancos) Seaway by sediment from the west and submerged under shoreline deposits included beach sand, deltaic mud 182 Chapter 7

7.13. The Mancos Shale of central Utah represents the offshore deposits that accumulated in the late Cretaceous foreland basin. Courtesy John Telford. and coal, and lagoonal silt. The nearshore sediments the nearby Sevier Orogenic Belt and the in-and-out extend as thin fingers to the east, where they even- oscillations of the Mancos Seaway. Marine deposits, tually pinch out into thick sequences of the open such as the Mancos Shale and Tropic Shale (fig. 7.13), marine deposits such as the Mancos Shale (fig. interfinger with nonmarine sediments in a compli- 7.11). The Late Cretaceous sediments that accumu- cated pattern that has taken geologists decades to lated in the Sevier foreland basin are thickest near- unscramble. est to their source and thin dramatically toward the In spite of its continual modulation, the coastal east. In central Utah, just east of the Sevier Orogenic plain was still an excellent habitat for dinosaurs. The Belt, the aggregate thickness of these sediments high Sevier Orogenic Belt was a superb watershed can exceed 18,000 feet. In Kansas, in the middle and provided the moisture to support a lush jun- of the Western Interior Seaway, where subsidence gle of trees and shrubs on the coastal plain. The cli- was much less and the sediment source more dis- mate appears to have been warm and humid, due in tant, the Late Cretaceous sediments are usually only part to the proximity of the sea. There was probably around 1,000 feet thick. The thick late Cretaceous a year-round growing season, ensuring a stable sup- rock record of central Utah is also extremely het- ply of food to sustain the terrestrial ecosystem. Cen- erogeneous and complex due to the active uplift in tral Utah was a warm, lush, and flourishing garden The Late Cretaceous 183

7.14. Late Cretaceous sedimentary rocks of southwest Utah (right) and central Utah (left). The Tropic Shale and Mancos Shale represent the maximum stage of the earliest transgression of the West- ern Interior Seaway into Utah. Coastal plain sediments that contain dinosaur remains compose portions of the Mesaverde Group in central Utah and the Straight Cliffs–Kaiparowits interval to the southwest. during the Late Cretaceous, a virtual paradise for a Blackhawk, Castlegate, and Price River Formations great variety of aquatic and terrestrial vertebrates, (fig. 7.14). Farther east, in the Book Cliffs north- including dinosaurs. The abundant life on the east of Green River, the Mesaverde Group consists coastal plain, coupled with the extremely high rate of as many as ten different rock units, including the of sediment accumulation, left a rich fossil record of Sunnyside Sandstone, the Sego Sandstone, and the the dinosaurs that thrived in this environment. Neslen Formation, among others. The sediments of the heterogenous Mesaverde Group in central Utah were derived from the Sevier Orogenic Belt and The Mesaverde Group and Equivalent Strata deposited in a variety of nonmarine and marginal Late Cretaceous sediments accumulated on the marine environments such as floodplains, braided coastal plain portion of the foreland basin every- stream systems, deltas, swamps, river channels, and where east of the Sevier Orogenic Belt. But two tidal basins (Van Wagoner 1995; Yoshida and oth- sequences of rock in Utah have produced most of ers 1996). the fossils that document the dinosaur faunas of Farther south, in the Kaiparowits Plateau region the time. In central Utah the strata that rest above between Lake Powell and Bryce Canyon, sedi- the Mancos Shale are known collectively as the ments of approximately the same age and type as Mesaverde Group. This package of rock layers is the Mesaverde Group represent the Straight Cliffs, thick, up to 3,000 feet or more in some places, and Wahweap, and Kaiparowits Formations (fig. 7.14). In is subdivided into several different formations. The these southern equivalents of the Mesaverde Group principal formations of the Mesaverde Group in the sediments originated from the southern por- the area around Price are (in ascending order) the tion of the Sevier Orogenic Belt and also from the 184 Chapter 7

7.15. A coal mine in late Cretaceous strata near Helper, Utah. The mine portals in the lower part of the photograph are in the gray, coal-bearing beds of the Blackhawk Formation. The massive cliffs along the skyline are exposures of the Castlegate Sandstone. Courtesy John Telford.

Mogollon highlands to the south, in central Ari- Both the Mesaverde Group and the Kaiparow- zona. The Kaiparowits sequence is over 6,000 feet its sequence contain coal deposits that formed in thick and consists mostly of river-deposited sedi- swampy environments near the western shore of the ment, with less common deltaic, lagoonal, and off- late Cretaceous seaway (fig. 7.15). Carbon County is shore sand and mud deposits (Eaton 1991). the heartland of Utah’s coal industry, and the chief The Late Cretaceous 185 producer of coal in this area is the Blackhawk For- modern analogues for the types of environments mation, a deltaic formation within the Mesaverde that must have existed on the narrow coastal plain Group. Coal is also found in central Utah in the Fer- of central Utah during the Late Cretaceous. Plant ron Sandstone, an older deltaic wedge that extends fossils indicate that a lush forest of sequoialike trees, into the Mancos Shale. In the Kaiparowits region magnolias, cypress trees, and palms rose above a the coal occurs primarily in the Straight Cliffs For- floor carpeted with ferns and sphagnum moss on mation, though it is also present in the older Dakota the ancient coastal plain of Utah (Nichols 1995). Formation. The coal of the Kaiparowits Plateau The jungles that thrived on the swampland run- region has not been mined as extensively as have ning through central Utah were populated by a rich the Mesaverde deposits of central Utah, but several fauna of vertebrates, including birds, turtles, fish, mining ventures have been proposed for the area primitive mammals, and, of course, dinosaurs. that target the billions of tons of coal still buried The presence of coal, an increasingly important beneath the surface. fossil fuel, has promoted the intense study of Utah’s Coal is the result of the accumulation of plant Late Cretaceous rock sequences by geologists (e.g., debris (such as leaves, twigs, and bark) in a stag- Peterson 1969; Doelling, 1972, 1975; Franczyk and nant body of water. Containing little oxygen and Pitman 1989; Olsen and others 1995). Recent stud- with an acidic chemistry resulting from the genera- ies (Eaton 1991; Nichols 1995; Olsen and others 1995) tion of humic acids by decaying vegetation, swamp have placed the age of both the Mesaverde Group water is like Mother Nature’s pickling solution. The and the Kaiparowits sequence in the range of 90–70 complete decomposition of the plant litter that falls million years. This corresponds to the Turonian into a swamp is prevented by the biologically hos- through Campanian ages of the Cretaceous. In both tile chemical environment. The layer of plant matter areas overlying formations such as the Canaan Peak on the bottom of a swamp gets thicker and thicker and the North Horn are younger: they record the with time. Eventually these organic residues become end of the Cretaceous period and, correspondingly, buried under sand and mud, when, for example, a the end of the age of dinosaurs. We will return to nearby stream floods or shifts its course. The bur- the issue of dinosaur extinction in the next chapter, ied plant debris underground can be compressed but first let’s examine the dinosaur fauna of the late and altered over millions of years into hard, black, Cretaceous coastal plain. These were the beasts of combustible coal. The formation of coal therefore the bayous. requires three conditions: (1) abundant vegetation, (2) standing bodies of stagnant water on a poorly Dinosaurs of the Mesaverde Group drained, nearly flat surface, and (3) eventual burial under additional layers of sediment. All three of Dinosaur bones are extremely uncommon in the these conditions existed on the narrow coastal plain formations of the Mesaverde Group. The Castlegate in central Utah during the Late Cretaceous, as indi- Sandstone produces an occasional scrap of bone, cated by the abundance of thick coal layers in the along with mostly isolated footprints and fossil Mesaverde Group and the Kaiparowits sequence. In wood (Yoshida and others 1996). But dinosaur foot- the modern world we find similar conditions along prints are sometimes remarkably abundant in the the Gulf Coast of Louisiana and Mississippi, where sandstones that are associated with layers of coal in the climate is warm, the vegetation is thick and jun- the Blackhawk Formation of the Mesaverde Group. glelike, and the swampy land lies close to the ocean Many footprints have been recovered from the (Gulf of Mexico). The swamps and bayous of the working coal mines in Carbon and Emery Coun- modern Mississippi delta are probably very good ties, where they are most commonly encountered 186 Chapter 7 on the bottoms of sandstone layers that buried the coal. After the coal is removed, the lower surface of the rock layer above is exposed as the ceiling of the mine. The overhead surface can be decorated with hundreds of footprints that hang precariously from the ceiling. I have heard several accounts of coal miners being injured by footprints that break away from the ceiling and fall to the floor of the mine. In addition, M. G. Lockley and A. P. Hunt (1995) document the hazards posed to coal miners from dinosaur footprints, including a 1969 fatality in western Colorado that resulted from injuries sustained when a miner struck his head on an overhead track. If the stories are true, then I suppose that we can consider such injuries to be rare cases of human-dinosaur interaction. Even though the dinosaurs and the human miners are separated by at least 75 million years, the activity of the dinosaur was undeniably linked to the human injuries. Dinosaurs smashing people is a popular theme in science fiction, but it evidently has actually happened in the mines of central Utah, albeit in a delayed manner. We refer to the objects on a coal mine ceiling as footprints, but in fact they are not. In most cases the actual footprint was impressed into the organic matter (peat) and mud on the bottom of the ancient swamps. This depression was later filled with sand or mud deposited by rivers that flowed into the bog. Eventually, the track-filling sediment hardened into the layer of sandstone or mudstone that rests above 7.16. Formation of dinosaur tracks in the coal swamps of the Mesaverde Group. Open depres- the coal (fig. 7.16). The “footprints” from Utah’s coal sions were left by dinosaurs walking through mines are actually the inverted replicas or casts of the peat layers in the swamps (top). These the original footprints made in the underlying coal. depressions were later filled with sand that was washed into the swamp. Millions of years later, In any event the cast can provide information on when the coal was mined from beneath the the gross foot morphology of its maker. In addi- sandstone, the “footprint” appeared on the roof tion, when numerous footprints are preserved as of the mine (bottom). a trackway on a coal mine ceiling, they record the movement of dinosaurs as they waded through the locomotion of some of the dinosaurs in the swamp swamp. Through the analysis of these footprint casts on the basis of footprint evidence. we can formulate some idea of the kinds of dino- The most common trackways and individual saurs and other creatures that lived in the swamps footprints from the Mesaverde Group are those evi- and their relative abundances. In addition, we can dently made by bipedal hadrosaurian dinosaurs that make some generalizations about the behavior and had a three-toed foot with blunt, hooflike claws (fig. The Late Cretaceous 187

leaving the deep prints in which the casting sediment later accumulated. In some places the density of hadrosaurian tracks in the Mesaverde sediments is so great (Parker and Balsley 1986; Lockley and Hunt 1995) as to suggest the movement of groups of dinosaur herbivores through the swamps. Among the larger hadrosaur footprints from Utah coal mines, tiny tracks less than 3 inches (7.5 cm) long and commonly oriented in a preferred direction are occasionally found (Carpenter 1992). These observations suggest that herds of hadrosaurs consisting of both juveniles and adults were moving about the swampy lowland, possibly migrating north and south, parallel to the late Cretaceous shoreline (Carpenter 1992). The stride length of individual prints in the trackways does not indicate rapid running but instead implies a lazy saunter through the boggy ponds. Some of these trackways veer around the petrified remains of tree stumps and occasion- 7.17. Dinosaur and other tracks from the Blackhawk For- ally reveal pauses or “resting stops” in the form mation (Mesaverde Group) of central Utah: A–B. large three-toed hadrosaur tracks; scale bar = 20 inches (0.5 of side-by-side hind foot prints that are unusu- m); C. a bird track, about 3 inches (8 cm) long; D. tiny ally deep (Parker and Balsley 1986). We infer from frog tracks, each a little less than an inch long; E. a four- this evidence that the hadrosaurs that left the coal toed track, probably made by a ceratopsian dinosaur, mine trackways were moving slowly together in about 16 inches long; F. a small theropod track with sharp claw impressions, about 11 inches long. A, D, E, herds of perhaps several dozen individuals. Tram- and F: based on photographs in Parker and Balsley pling through the swamps, they periodically paused 1986; B and C: after Lockley and Hunt 1995. to browse on the dense vegetation that must have grown all around them. 7.17A, B; Lockley and Hunt 1995; Parker and Row- Another clue to the identity of these track-mak- ley 1989). The tracks are most numerous in the coal- ing hadrosaurs was discovered recently in the form rich Blackhawk Formation but are known from of skin impressions associated with fragmentary other horizons in the Mesaverde Group as well. skeletal remains preserved in the Neslen Forma- These presumed hadrosaur tracks range in size from tion of the Mesaverde Group (Anderson and others tiny prints, less than an inch long, to gigantic tracks 1999). The skin of the hadrosaur was covered by tiny nearly 3 feet (1 meter) in length. The larger hadro- tubercles or bumps around 0.1 inch (2–3 mm) in saur tracks signify the presence of some very large diameter, with larger rounded tubercles, up to about herbivores: they must have been made by an animal half an inch, located on the dorsal surface. Thus that weighed over 10 tons! The large feet of the had- the skin appears to have had a bumpy, beaded tex- rosaurs, with three broad and widely splayed toes, ture distinct from the folded, leathery skins of mod- were well suited for supporting such massive ani- ern mammals such as hippos that occupy similar mals on the soft, spongy bottom of the coal swamps. habitats and ecological niches. The identity of the Nonetheless, these herbivores still sank into the peat large Mesaverde hadrosaurs has not yet been estab- and mud as much as 2 feet as they walked along, lished with certainty, but they were probably similar 188 Chapter 7

7.18. A dinosaur trackway in the Ferron Sandstone Member of the Mancos Shale near Moore, Emery County. The trackway is exposed on the bottom of a sandstone block that has fallen from the cliffs in the distance. The tracks were made by an unknown dinosaur walking along the edge of the late Cretaceous seaway in central Utah. Courtesy John Telford. to Gryposaurus or Parasaurolophus, both of which environments adjacent to the coal swamps, includ- occur in strata of about the same age in southern ing beach and deltaic sands (fig. 7.18) and river- Utah, Montana, New Mexico, and western Can- deposited sand in southwest Utah (Milner and ada (see below). But neither of those hadrosaurs are others 2006). commonly as large as the animals indicated by the biggest tracks from the Mesaverde Group of cen- Late Cretaceous Dinosaurs of Southern Utah: tral Utah. More complete skeletal material will be A Spectacular Array required before we can we sure which hadrosaurs left the tracks preserved in the coal swamp sedi- Until about fifteen years ago little was known about ments of Utah. Ornithopod dinosaurs evidently the late Cretaceous dinosaur faunas of southern and were continually on the move along the late Cre- southwest Utah. Scrappy remains had been discov- taceous coastal plain of central Utah. Tracks likely ered that documented the presence of large Orni- made by hadrosaurs are relatively common in sedi- thopods (Weishampel and Jensen 1979) and small mentary rocks representing a variety of depositional birdlike predators (DeCourten and Russell 1985), The Late Cretaceous 189

7.19. Map of the Grand Staircase–Escalante National Monument with outcrops of the late Cretaceous Wah- weap Formation indicated. Other late Cretaceous formations, such as the Kaip- arowits Formation and Straight Cliffs Forma- tion, are also widely exposed in this region. From Kirkland 2001. but few other well-preserved dinosaur fossils were of dinosaurs have been named from the late Cre- known from the Straight Cliffs, Wahweap, and Kaip- taceous strata of the GSENM since intensive sur- arowits Formations. That situation changed dramat- veying began; many more will undoubtedly be ically in 1996, when President Bill Clinton set aside identified in the years to come. nearly 2 million acres of wilderness and adjacent lands as the Grand Staircase–Escalante National Dinosaurs of the Straight Cliffs–Wahweap– Monument (GSENM). Much of the land between Kaiparowits Sequence Bryce Canyon and Lake Powell lies within the boundaries of the GSENM (fig. 7.19) and is remote In southern Utah strata approximately equiva- wilderness, difficult to access and far from popu- lent in age to the Mesaverde Group of central Utah lation centers. Prior to the creation of the national comprise the Straight Cliffs, Wahweap, and Kaip- monument paleontologists only infrequently vis- arowits Formations (fig. 7.14). These rock units con- ited the vast exposures of late Cretaceous strata in sist of sandstone, mudstone, shale, and coal that the magnificent but secluded wildlands. Since 1996, were deposited by rivers, in swamps and lagoons, however, scientists from a variety of organizations, and along the shore of the Western Interior seaway including the Utah Museum of Natural History, the between about 80 and 75 million years ago (Lawton Bureau of Land Management, and the Utah Geo- and Bradford 2011). During most of the Late Creta- logical Survey, have been systematically surveying ceous the coastal plain was relatively wide in south- the lands within the GSENM for vertebrate fossils. ern Utah, and the dinosaurs and other terrestrial What they have discovered in recent years is noth- creatures had more prime habitat to occupy than ing less than stunning: a dinosaur fauna so rich and was the case in central Utah. All three of the for- diverse that the GSENM can now be considered mations in the late Cretaceous sequence have pro- one of the most important regions in the world for duced the remains of dinosaurs. The abundant and dinosaur paleontology. At least a dozen new species diverse dinosaur fossils collected from these strata 190 Chapter 7 are accompanied by the remains of many other vertebrates that shared the coastal plain habitat during the late Cretaceous. The Straight Cliffs Formation has yielded the fossils of turtles, crocodilians, dinosaurs, and mammals, along with marine invertebrates in the portions of the formation that were deposited in estuaries, lagoons, and bays near the coast (Eaton 1991; Eaton and others 1999). Plant fossils of gymnosperms, ferns, mosses, and angiosperms are also common, especially microscopic grains of pollen (Nichols 1995). The small primitive mammals of the Straight Cliffs Formation have been extensively studied (Eaton and Cifelli 1988; Cifelli 1990a, 1990b; Eaton 1995) because their tiny fossils are relatively abundant and mammal remains of the same age are very rare elsewhere in the world. The mammal fauna includes many varieties of small, ratlike creatures, such as symmetrodonts, multituberculates, and marsupials (Cifelli 1990b; Eaton 1995). Hordes of these rodentlike mammals must have lived in the mossy forests and beneath the fern thickets of the wide coastal plains. The dinosaur remains from the Straight Cliffs Formation have not 7.20. Skull of Diabloceratops eatoni from the Wahweap been as intensely studied and are very fragmentary, Formation of southern Utah. Scale bar = 20 inches (50 consisting mainly of small, isolated teeth. Even from cm). Based on Kirkland and DeBlieux 2010. these meager data, however, it has been established that hadrosaurs and several types of theropods were from the isolated and fragmentary fossils produced present in southern Utah and were accompanied by the Straight Cliffs Formation (Parrish 1991). In by the armored ankylosaurs (Parrish 1991). In com- more recent years, however, several exciting dis- parison to the abundant fossils found in the over- coveries of partial skeletons in the Wahweap For- lying Wahweap and Kaiparowits Formations, the mation of the GSENM region have revealed the remains from the Straight Cliffs Formation are presence of several types of horned dinosaurs (cera- rather scrappy. We can form a much more detailed topsians) that had never been seen before (Kirkland picture of the late Cretaceous dinosaur communi- 2001; Kirkland and DeBlieux, 2007, 2010). Cera- ties in Utah on the basis of fossils found in the sand- topsians are familiar to many people because the stone and mudstone layers above the Straight Cliffs best-known genus, Triceratops, commonly has been Formation. Let’s have a look. featured in movies, books, toys, and posters. Tric- eratops (“three horn face”) is a good model for the general body plan of all of the dinosaurs that belong Dinosaurs of the Wahweap Formation the clade Ceratopsia, though with considerable vari- In the 1990s the dinosaurs of the Wahweap Forma- ations on this theme, as we will soon see. Triceratops tion seemed to be similar to the aggregate known had two prominent brow horns, an upward curving The Late Cretaceous 191

evokes an image of the mulching machines that arborists use to turn tree branches into wood chips. In addition, the teeth of the ceratopsians are recessed inward, forming prominent cheek pockets on either side of the mouth. In life the cheek pockets of ceratopsians were probably stuffed with plant matter that was forced through the bladelike dental batteries. It would have been fascinating to watch a ceratopsian feed: swollen cheeks packed with stiff and stringy fodder, jaw muscles swelling at the base of the frill, and the beak continuously shearing off fronds and branches to replace the swallowed chop- pings. Thus the ceratopsians seem to have been well adapted to processing tough and/or fibrous vegetation, while the hadrosaurs (or “duckbills”) might 7.21. Jaw mechanics of the ceratopsian dinosaurs. have preferred softer, leafy food. The nostrils of ceratopsians were very large and nose horn, and a broad frill extending over the neck housed in a deep pocket just behind the beak. The from the back of the skull. While these features are paired nasal bones that form the upper part of the typical of the Ceratopsia, many other distinctive nostrils are usually fused, and a hump of bone that traits define this clade of ornithischian dinosaurs. supported the nose horn sheath projected upward. Unique to the ceratopsians is a beaklike bone, the The nose horn cores were as long as 2 feet (0.6 rostral, which joins the premaxilla at the tip of the meter) in some species of ceratopsians (the actual snout (fig. 7.20). The surface of the rostrum is wrin- horns would have been even longer in life), but they kled and rough, indicating that a horny sheath cov- are barely noticeable in others. The brow horns are ered the bone in life. The snout of ceratopsians was also variously developed in ceratopsians, although tipped with a vicious, sharp-edged beak that would all arise from the bones that form the upper border have been extremely effective in chopping vegeta- of the orbit (eye socket). The jugal (cheek) bones on tion. Except for the closely related psittacosaurs, no the sides of the skull below the eye had a spikelike other group of dinosaurs possessed such a parrot- process that projected out and down, giving cera- like snout. topsians two additional hornlike protuberances on The teeth of ceratopsians were arranged in verti- the head. cal rows that were locked together to form a contin- The characteristic head frill of ceratopsians was uous cutting blade along the edge of the jaws. The formed mainly by the highly elongated squamo- upper teeth passed just outside of the lower teeth sal and parietal bones. In other dinosaurs these (fig. 7.21) each time the massive jaws were closed two bones normally make up portions of the top by powerful muscles anchored near the back of the and back of the skull. Thus the frills of ceratop- head and on the frill. As the hard enamel edges of sians developed as the back of the skull “grew” out the teeth sheared past each other, vegetation was over the neck. The frills may be nearly circular, chopped into small pieces. Coupled with the beak at heart-shaped, or triangular and in some genera are the snout, ceratopsian jaws were no doubt capable decorated with knobs of bone or spikes arranged of chopping even the toughest vegetation. Contem- around the periphery. In addition, many ceratop- plating the beak, teeth, and jaws of the ceratopsians sians had circular or elliptical openings in the frills 192 Chapter 7 that probably served for the attachment of jaw mus- weighing a ton or more. Its skull was more than 4 cles. The frills, horns, and massive skull bones gave feet (a little over a meter) long from the tip of the the ceratopsians the largest heads of any land ani- snout to the back of the bony frill (fig. 7.20). Two mal that ever lived. The skulls were as long as 9 feet large curving horns projected upward and outward (3 meters) in the largest ceratopsians, almost the size from the back of the frill, giving Diabloceratops a of a small car! devilish appearance and providing the basis for the The vertebral column and limbs of the ceratop- genus name. The frill also had two large openings, sians are well designed to support a large quadrupe- and its border was decorated by numerous knobs dal animal. The cervical (neck) vertebrae are large and blunt spikes of bone. The larger ceratopsian and partially fused to support the gigantic head. The dinosaurs like Diabloceratops belong to the family backbone was arched upward and braced through Ceratopsidae, which is traditionally subdivided into the hip region by a network of bony rods. The tail two distinct subfamilies: the Centrosaurinae and the of ceratopsians is relative short and not particu- Chasmosaurinae (Lehman 1990; Dodson and Cur- larly massive. The limbs are very robust and solidly rie 1990). The Centrosaurinae are the smaller and attached to the pelvis and shoulder girdle. The hind presumably more primitive ceratopsids, with a rel- limbs are massive columns that were positioned atively short frill in which the squamosal bone does vertically beneath the body; but some controversy not reach to the back edge. In addition, the Cen- has arisen about the positioning of the forelimbs. trosaurinae usually have a nose horn that is larger Some paleontologists (e.g., Johnson and Ostrom than their brow horns and ornate frill margins. Cen- 1991) argue that the forelimbs of the ceratopsians trosaurus, with its single large nose horn, and the were splayed outward from the midline, while oth- spiky-frilled Styracosaurus are good examples of the ers assert that they were placed vertically beneath Centrosaurinae. The familiar Triceratops exhibits the body, similar to the hind limbs (Paul 1991; Lock- the features that characterize the Chasmosaurinae: a ley and Hunt 1995). The feet were very broad, with long, relatively smooth-bordered, frill in which the widely splayed toes tipped by large hooflike claws. squamosal bones reach the back edge, brow horns Overall the skeletal architecture of the ceratopsians larger than the nose horn, and a large body size. In seems better designed for weight-bearing than for describing Diabloceratops, Kirkland and DeBlieux speed. Nonetheless, the ceratopsians could proba- (2010) noted a primitive pattern of openings in the bly move quite effectively over land. Mass accumu- skull, along with some other details of cranial bones, lations of ceratopsian remains, representing scores that suggested a relationship to the centrosaurids, a of juveniles and adults, are not uncommon in the group that would become much more abundant and late Cretaceous bone beds of Montana and Alberta diverse in the later Cretaceous. (Currie and Dodson 1984). Such bone beds sug- Recent and ongoing work by paleontologists in gest strong herding behavior among the ceratop- the Wahweap Formation is continuing to reveal the sians, but whether they moved at a slow walk like presence of a diverse dinosaur fauna in southern elephants or galloped along like rhinos is still debat- Utah approximately 78–79 million years ago. T. A. able. Altogether the ceratopsians are a remarkable Gates and others (2011) recently described the skull group of highly specialized ornithischians. of Acristavus gagslarsoni, a large hadrosaur with The best known of the Wahweap ceratopsians a smooth, unadorned skull (fig. 7.22). Though the is Diabloceratops eatoni, named by J. I. Kirkland postcranial skeleton is unknown, Acristavus must and D. D. DeBlieux (2010) on the basis of a nearly have been one of the larger herbivores roaming the complete skull. Diabloceratops was a large animal, coastal plain of southern Utah, with a total length of probably some 20 feet (about 7 meters) long and 25–30 feet (8–10 meters). Small teeth have also been The Late Cretaceous 193

limbs and feet tipped with the size and type of claw that could have made the digging marks.

Dinosaurs of the Kaiparowits Formation

Dinosaur fossils are much more abundant in the Kaiparowits Formation than in any other late Creta- ceous formation in southern Utah. Consequently we know much more about the dinosaur faunas of this formation than of the communities preserved in the Straight Cliffs and Wahweap Formations. The Kaip- 7.22. Skull of Acristavus gagslarsoni, a hadrosaur or “duckbill” dinosaur from the Wahweap Formation of arowits Formation is up to 2,800 feet thick and con- southern Utah. The skull was probably about 28 inches sists mostly of gray mudstone and weakly cemented, long. Based on figures from Gates and others 2011. fine-grained sandstone. These deposits accumulated on the floodplains of the broad coastal plains found in the Wahweap Formation that suggest the and to a lesser degree on the boggy surfaces of del- presence of at least several different theropods of tas near the shoreline of the seaway. Where they are modest size along with many different types of small exposed, the soft sediments of the Kaiparowits For- ratlike mammals (Kirkland 2001; Eaton and others mation weather into blue-gray badlands that are a 1999). Some of these small dinosaurs may have had fossil hunter’s paradise. Many well-preserved dino- a very specialized method for preying on the small saur fossils have been collected in the area known as mammals that lived in ground burrows beneath the “The Blues,” along Utah Highway 12 between Tropic underbrush. E. L. Simpson and others (2010) have and Escalante (fig. 7.23). In addition, the remains of described round structures in the Wahweap Sand- turtles, crocodiles, primitive mammals, and many stone that seem to be subsurface cavities that were kinds of plants occur in the Kaiparowits Formation, later filled with sediment. The cavities appear to sometimes in great abundance (Boyd and others have been connected by tunnels, suggesting that 2009; see also Gregory 1951; Lohrengel 1969; Cife- they were excavated by digging animals that exca- lli 1990a; Eaton 1991; Titus and Anderson 2011). The vated underground dens, similar to those of many probable age of the Kaiparowits Formation is about modern ground-dwelling rodents. Most intriguing, 74–76 million years (Lawton and Bradford 2011; though, are the downward-arching grooves that are Roberts and others 2005). commonly found in or near the underground cavities. These grooves may well have been made by Ceratopsians of the Kaiparowits Formation small theropod dinosaurs digging into the ground Several types of ceratopsian dinosaurs are known to reach their food—the terrified mammals hiding from the Kaiparowits Formation. Two of the best in their underground pockets. Simpson and others known are Utahceratops gettyi and Kosmoceratops (2010) make a compelling argument that these trace richardsoni, both first described by paleontologists fossils provide rare evidence of dinosaurs digging in 2010 (Sampson, Loewen, and others 2010) on the for prey. The most likely candidates for the digging basis of fossil material representing several individ- dinosaurs are the relatively small ornithomimid and uals of each species. Utahceratops was the larger of troodontid predators that are known from other the two, reaching about 20 feet (7 meters) in total horizons within the Wahweap-Kaiparowits interval. length, including 7 feet (about 2 meters) for its mas- Both types of small theropods had powerful hind sive skull (figs. 7.24, 7.25). The short horns over 194 Chapter 7

7.23. Outcrops of the Kaiparowits Formation in “The Blues” in the Grand Staircase–Escalante National Monument. Photo by Frank DeCourten.

7.24. Reconstructions of the skeletons of the ceratopsian dinosaurs Utahceratops gettyi (A, left) and Kosmocera- tops richardsoni (B, right) from the Kaiparowits Formation of southern Utah. Scale bar = 3 feet (1 m). From Sampson, Loewen, and others 2010. the eyes of Utahceratops projected laterally rather of the skull of Kosmoceratops was proportionately than forward as in Triceratops (fig. 7.25). Kosmocer- smaller than in Utahceratops, and the paired open- atops was smaller, about 14 feet (4.5 meters) long, ings were less pronounced and located farther back with a somewhat more slender build than Utah- on the frill. Fifteen horns or hornlike projections ceratops. The bony shield extending from the back decorated the skull and frill of Kosmoceratops, a The Late Cretaceous 195

7.25. Reconstruction of the complete skull of Utahcera- tops gettyi seen from the top (A, dorsal view) and from 7.26. Reconstruction of the complete skull of Kosmocer- the side (B). Scale bar = 3 feet (1 m). From Sampson, atops richardsoni seen from the top (A, dorsal view) and Loewen, and others 2010. from the side (B). Scale bar = 3 feet (1 m). From Samp- son, Loewen, and others 2010. number unequaled by any other known ceratopsian dinosaur (fig. 7.26). Oddly, eight of these horns were rather fragmentary, consisting mostly of sin- at the back of the skull curve forward to overlie the gle bones, short vertebral series, skull fragments, two small openings in the frill, while the two horns and (rarely) a few articulated bones. For many years on either side curve outward. The nose horn of Kos- Parasaurolophus was the only genus clearly doc- moceratops was not prominent and was somewhat umented by diagnostic but scrappy fossil mate- flattened from side to side so that it more closely rial that included portions of its distinctive curving resembled a blade than a spike. Utahceratops and crest (Weishampel and Jensen 1979). More recently, Kosmoceratops clearly were two distinct species of however, new fossil material collected from the ceratopsian dinosaurs; it would have been easy to GSENM region has revealed the existence of a sev- recognize their differences as they prowled the Kai- eral different ornithischian dinosaurs in the Kaip- parowits coastal plain during the late Cretaceous. arowits fauna, including several duckbills previously However striking the contrasts between these two unknown in this part of Utah (Gates and Sampson species may have been, both ceratopsians were rela- 2007). In addition, the discovery of “bone beds” in tives within the subfamily Chasmosaurinae. the Kaiparowits Formation that consist entirely of the remains of hadrosaurs (Jinnah and others 2009) Hadrosaurs of the Kaiparowits Formation suggests that these large herbivores roamed about Judging from the abundance of their fossils, had- the coastal plain in sizable herds. rosaurs (duck-billed dinosaurs) were the fairly com- The remains of Parasaurolophus thus far col- mon dinosaur herbivores of the Kaiparowits fauna. lected from the Kaiparowits Formation are very Until recently, however, the remains of hadrosaurs scrappy, consisting of a few pieces of at least two 196 Chapter 7

and old of the same species. If so, it would have been easy to distinguish males from females (or young from adults) in a herd of Parasaurolophus on the basis of the inferred sexual dimorphism of their crests: the longer crests probably signified males, while the shorter, bowed crests indicated females. If the development of the crest was a secondary sexual trait, then the juveniles probably had very small crests that developed variously, depending on gender, as the animals grew to maturity (Dodson 1975). Whatever its size or shape, the tubular bony crest on the skull of Parasaurolophus is the most peculiar and distinctive characteristic of the genus. This crest was formed from the grossly modified premaxillary and nasal bones that extend backward, project- 7.27. Skulls of two species of Parasaurolophus. The ing over the top of the head by as much as 3 feet (1 long snorkel-like crest was formed from the premaxil- meter) in some species. In addition, these bones are lary and nasal bones that extended far behind the head. P. walkeri (bottom) had a longer and straighter crest curved into a tubular form that surrounds a spa- than P. cyrtocristatus (top). Scale bar = 2.5 inches (6 cm). cious nasal cavity inside. The function of the odd After Weishampel and Horner 1990. crests on the skulls of Parasaurolophus and other lambeosaurs has been a subject of great discus- skulls, a few vertebrae, rib fragments, and other iso- sion among paleontologists for many years. These lated material such as teeth. Fortunately the skull crests have been interpreted as defensive weap- elements reported by D. B. Weishampel and J. A. ons, humidifiers, foliage deflectors, and accessory Jensen (1979) included a portion of the very dis- breathing devices for underwater feeding. For a tinctive crest that adorned the head of Parasauro- variety of good reasons none of these ideas for the lophus (fig. 7.27) and its relatives in the subfamily primary function of the crests are currently favored Lambeosaurinae, a group of specialized duckbills by the majority of paleontologists. Instead the crests with elaborate cranial ornamentation. The original are now generally regarded to have served primar- species Parasaurolophus walkeri was first identified ily for communication between individual lambeo- from fossils collected in Alberta. This species had an saurs in a group. The crest of Parasaurolophus was enormous elongated crest that made the skull over 5 probably used for both visual and auditory signaling feet (1.5 meters) long. The partial skulls of Parasau- (Weishampel 1981; see also Hopson 1975). rolophus from Utah appear to have been more sim- Because the size and shape of the crest in vari- ilar to a distinct species, P. cyrtocristatus, that had ous types of lambeosaurs are unique to each species, a smaller and more strongly curved crest. P. c y r- its form would allow these dinosaurs to recognize tocristatus was first identified on the basis of fos- members of their own genus and species. A stray sils found in New Mexico, so it makes sense that the Parasaurolophus could easily have distinguished Utah specimens appear to be more similar to it than the graceful, snorkel-crest of its own kind from, for to the larger specimens recovered far to the north. example, the circular plate that decorated the heads It is possible that these two species of Parasaurolo- of Corythosaurus, a lambeosaur relative. Within a phus (along with a third one, also known from New group of Parasaurolophus individuals, communi- Mexico) may represent males and females or young cation might also have included sounds that were The Late Cretaceous 197 generated within the hollow tubes of their crests. Weishampel (1981) has shown that the hollow tubes in the crest formed a pathway for air brought in and exhaled out through the nose. By shunting air into different portions of the tubes and controlling the rate of airflow, Parasaurolophus could have generated deep bellows and resonating calls. A trombone works on the same principle to create a variety of sounds. Perhaps different sounds were used to sig- nal danger, to attract mates, to announce feeding opportunities, and to communicate with juveniles in a herd. Given the striking differences in the size and shape of the crests in P. walkeri and P. cyrtocristatus, the sounds and sights emanating produced by these structures were no doubt very distinctive to the members of each species. 7.28. Cross-sectional view of hadrosaur teeth and jaws. The teeth in the upper jaws could slide outward over the Parasaurolophus was a large animal, up to about teeth of the lower jaws, shredding and mashing plant 35 feet (about 12 meters) long as an adult. It was also matter held in the cheek pouches. heavily built, with a massive shoulder and pelvic girdle. The forelimbs were smaller than the hind limbs, surfaces formed by the lower tooth rows (fig. 7.28). but only modestly so, and the hands were tipped Deep cheek pockets allowed the hadrosaurs to hold with blunt, hooflike claws. These observations sug- a large mass of vegetation in their mouths as it was gest that Parasaurolophus was a habitual quadruped being pulverized. This motion, coupled with the but could easily rear up on its hind legs as well. As unique arrangement of teeth, gave hadrosaurs the in other hadrosaurs, the stiff tail of Parasaurolophus ability to turn virtually any plant material into a was flattened from side to side and seems well suited highly digestible pulp. This efficient way of process- for propelling the animal through water. Parasau- ing plant food probably evolved in response to the rolophus was a masterful plant-eater, with elaborate increasing dominance and diversification of angio- dental batteries anchored to massive jaws that were sperms in the global flora of the Cretaceous. In the powered by huge jaw muscles. The toothless bill of heavily forested swamplands of the late Cretaceous Parasaurolophus was expanded but not quite as wide in central Utah the success of such specialized her- and “ducklike” as in the noncrested hadrosaurs. Like bivores is certainly no mystery. other hadrosaurs, Parasaurolophus had a highly It is also no surprise that several different types specialized dentition and a broad, expanded, and of hadrosaurs occupied the broad coastal plain of toothless snout that is the basis for the term “duck- the late Cretaceous. Gryposaurus monumentensis is bill” applied to such dinosaurs. Behind their bills another hadrosaur that has been identified from the the jaws contained hundreds of teeth arranged in late Cretaceous strata in the GSENM, as the spe- side-by-side rows that formed very effective grind- cies name suggests (Gates and Sampson 2007). Gry- ing surfaces. Each long, curving tooth in the den- posaurus is also known from Canada and Montana, tal battery had a layer of hard enamel on one side where its remains were first described in the early that created many small ridges on the grinding sur- 1900s. The Utah specimens appear to have pos- face. As hadrosaurs chewed their plant food, the sessed a boxier and somewhat heavier skull, how- upper jaws could slide outward over the grinding ever, with a more robust “duckbill” than its relatives 198 Chapter 7

7.30. Skull of Gryposaurus monumentensis, about 3 feet long, at the Utah Museum of Natural History. Photo by Frank DeCourten.

without the flamboyant crests and blades of hadrosaurs such as Parasaurolophus. Most of the hadrosaurines had a broad, vertically flattened tail that might have assisted their movement through swamps and ponds (fig. 7.31). Though the forelimbs of the hadrosaurines were much smaller than the hind limbs, the “fingers” 7.29. Skulls of Utah’s Gryposaurus monumentensis (top) bore small hooflike claws that indicate their use in and Gryposaurus notabilis from Canada (bottom). Scale bar in both = 2.5 inches (6 cm). Based on reconstruc- locomotion and imply at least occasional quadru- tions by Gates and Sampson 2007. pedal habits. Such hadrosaurs have often been portrayed as semiaquatic dinosaurs that spent most of to the north (fig. 7.29; Gates and Sampson 2007). their time in water, feeding on soft aquatic plants. Gryposaurus had a pronounced “bump” on its nose This image might be a bit exaggerated: Gryposau- above and slightly in back of the nostrils (fig. 7.30). rus probably generated a powerful bite, which, along This hooked nose is similar to the hadrosaur Kri- with its battery of shredding teeth, could easily have tosaurus, known from New Mexico and possibly processed even the toughest nonaquatic vegetation. Montana as well. In fact Gryposaurus and Kritosau- Thus it is reasonable to envision Gryposaurus herds rus are so similar that confusion between these two wandering continuously through the damp jun- genera among paleontologists lingers to the present gle in small groups, feeding as they went, walking time and has been a continuous challenge in con- over the spongy forest floor while wading or swim- structing the hadrosaur family tree. While much of ming through the bayous of southern Utah 75 mil- the postcranial skeleton of the Utah specimens of lion years ago. Gryposaurus remains unknown, both Gryposaurus In addition to the skeletal remains of Parasauro- and Kritosaurus appear to have been large animals, lophus and Gryposaurus, paleontologists have dis- 25–30 feet (8–10 meters) long and weighing between covered many other fossils of hadrosaurid dinosaurs 1 and 2 tons (fig. 7.31). Gyposaurus lacks any cra- in the late Cretaceous strata of southern Utah that nial decorations (other than the arching nose) and are too fragmentary to identify to genus or species therefore belongs to the Hadrosaurinae, the subset level. Some of these fossils include skin impressions of duckbills that included the smooth-headed types left in the enclosing sediment that preserves the The Late Cretaceous 199

7.31. Skeleton of Kritosau- rus, a large hadrosaur very similar to Gryposaurus. The larger individuals of such herbivorous dinosaurs might have weighed as much as 2 tons in life and exceeded 30 feet in length. pattern of the scaly integument possessed by these species were indeed very large bipedal dinosaurs. dinosaurs (Herrero and Farke 2010). These fossils Though we cannot be sure which hadrosaur left any suggest that duckbills known from the Kaiparowits particular footprint, the size of the preserved tracks Formation had thick skin armored with small scales is consistent with a large adult Gryposaurus or Para- and polygonal tubercules as large as about 0.2 inch saurolophus. Perhaps the hadrosaurs were moving to (5 mm). The skin is sometimes deeply folded, as is breeding grounds and nesting areas or possibly they common in mammals such as elephants and rhi- migrated seasonally in search of food. In either case noceroses that also have a thick hide. The skin of the it would have been an amazing sight to watch herds large hadrosaurs may have borne a pattern of stripes of these thunderous reptiles marching across the of spots that afford some concealment via camou- coastal plain and through the jungles of late Cre- flage (fig. 7.32). Also, many footprints and trackways taceous Utah. Imagine the sights and sounds that in the Kaiparowits and coeval rocks suggest herd- we might have witnessed during the Parasaurolo- ing and migratory behavior of the hadrosaurs that phus mating season or a Gryposaurus herd migrat- lived on the coastal plain and in the coal swamps ing from its nesting grounds on the Kaiparowits of southern Utah. The hind feet of most hadro- coastal plain. The bellowing males might have been saurs left fairly distinctive footprints, with three seen with crests ablaze with color, cavorting through broad toe impressions with blunt imprints of hoof- the herd while sparring with their 2-ton competitors like claws (fig. 7.17A, B). The forelimbs and hands or confronting predators with their bulk and their of hadrosaurs rarely touched the ground in these calls. The females may have prodded their young mostly bipedal animals, and preserved tracks of to keep up with the herd, using screeching wails to the fore feet are much less common. Based on the stop those who wandered too far afield. It would abundance and distribution of hadrosaur tracks in have been impossible not to notice a passing herd of the late Cretaceous strata of central and southern duckbills! Utah, a lot of north-south duckbill traffic occurred Along with the many hadrosaur tracks, the on the broad coastal plain. It also appears that some Mesaverde sediments of central Utah have produced of the hadrosaurs occasionally migrated west, away less abundant footprints that reveal the presence of from the coast, into the upland areas at the base of many other types of vertebrates in the Late Creta- the Sevier Orogenic Belt (Milner and others 2006). ceous coal swamps (fig. 7.17C–F). Birds lived among Some of the hadrosaur tracks approach 3 feet (1 trees in the dense jungles, while frogs thrived in the meter) in length, indicating that some of these ponds and peat bogs (fig. 7.17C–D; Robison 1991). 200 Chapter 7

7.32. Parasaurolophus in the dense Kaiparowits jungle, with Avisaurus, a primitive bird, perched on the tree limbs in the background. Illustration by Carel Brest van Kempen. The Late Cretaceous 201

Rarely, four-toed impressions are found (fig. 7.17E), probably made by quadrupedal horned ceratopsian dinosaurs. Some of the smaller three-toed dinosaur tracks have very narrow toe impressions that end in sharp tips (fig. 7.17F). These were almost certainly made by small theropods that stalked the hadrosaur herds and other prey animals through the swamps. With so many herbivorous creatures to prey upon, many types of predators must have lived in southern Utah during the late Cretaceous. Until recently, however, the remains of predatory dinosaurs were virtually unknown from the Kaiparowits Forma- 7.33. Foot of Ornitho- tion. Exciting new discoveries made over the past mimus velox from the twenty-five years are now beginning to provide a Kaiparowits Forma- tion of southern Utah. glimpse into a spectacularly diverse array of carniv- The metatarsals of the orous dinosaurs that pursued the ceratopsians, had- middle foot are highly rosaurs, and other prey animals across the coastal elongated, as in an ostrich, giving this small plain. theropod a long stride. Scale bar = 2.5 inches Dinosaur Predators of the Kaiparowits Formation (5 cm). Ornithomimus Until 1985 only a few isolated theropod teeth, that make this group of dinosaur predators very foot and tail bones, and vertebrae were known from interesting. the Kaiparowits Formation (Gregory 1951). The Ornithomimus is the namesake genus for the first Kaiparowits theropod identified to the genus family Ornithomimidae, a remarkably birdlike and species level was Ornithomimus velox, identi- group of small theropods. The ornithomimids were fied in 1985 on the basis of a nearly compete hind small to medium-sized dinosaurs, with long slender limb, partial pelvis, and several caudal vertebrae legs, a lightly built skeleton, and a graceful neck that (DeCourten and Russell 1985; fig. 7.33). Though supported a small skull (fig. 7.34). In their general some paleontologists have questioned the spe- proportions the ornithomimids bore an extraordi- cies-level identification of this material (Zanno and nary resemblance to the modern ratite birds, such others 2010), additional fossils discovered more as ostriches, emus, and rheas. But most paleontol- recently in the Kaiparowits Formation clearly docu- ogists consider the ornithomimid dinosaurs an off- ment the existence of the genus Ornithomimus, or at shoot of the main evolutionary branch of dinosaurs least dinosaurs very much like it, in southern Utah (the Maniraptora) that leads directly to modern 75 million years ago. While no complete skeletons birds. Nonetheless, the ornithomimids were broadly have yet been discovered, the abundant isolated fos- related to birds, even if they are not their direct sils of ornithomimid dinosaurs suggest that several ancestors. different types of birdlike predators may have pop- The snout of Ornithomimus was formed by a ulated the Kaiparowits coastal plain. However many toothless beak, with sharp edges of bone where the species of this genus existed in Utah, they probably teeth would normally be. The absence of teeth in all shared the same set of basic anatomical features Ornithomimus, coupled with the flexibility of the 202 Chapter 7

7.34. Skeleton of an ornithomimid dinosaur, Struthiomimus, from the late Cretaceous of western Canada. Ornithomimus from the Kaiparowits Formation in Utah was very similar in size and appearance to this 12-foot-long predator.

beak, has led some paleontologists to conclude that Kaiparowits Formation of Utah. Closer to Utah it was probably an omnivore rather than a strict Ornithomimus is known from the late Cretaceous predator, as might be implied by its classification of New Mexico (Lucas 1993), Colorado (DeCour- as a theropod. This is a reasonable interpretation, ten and Russell 1985), Wyoming (Estes 1964), and because Ornithomimus also had well-developed Canada (Russell 1972). These little theropods were forelimbs and a hand that could grasp and manip- probably quite numerous in Utah and seem to have ulate small objects. It had large eyes and, relative to been perfectly adapted for their role as opportunis- its size, a very large brain. Furthermore, the elon- tic omnivores. But we might not have seen Orni- gated feet, ankles, and limbs of Ornithomimus (fig. thomimus at all if we took a safari to southern Utah 7.33) were designed for speed and mobility. This all during the late Cretaceous. It was probably a timid suggests that Ornithomimus was a swift, stealthy and secretive animal, perhaps even nocturnal, that animal that could exploit many different sources would have detected us long before we noticed it. A of food. The Kaiparowits ecosystem would have muted screech and the rustle of foliage might have afforded a varied menu to a quick-moving, crafty been our only hint of its presence in the jungles omnivore like Ornithomimus. Lizards, insects, prim- around us. itive mammals, the fruit of angiosperms, carrion, Hagryphus turtles, fish, and perhaps even the eggs and juveniles As a birdlike dinosaur predator, Ornithomimus of dinosaurs may all have been included in the diet appears to have had some company of the Kaip- of these versatile creatures. Conversely, it is difficult arowits coastal plain. In 2005 paleontologists from to imagine Ornithomimus, only about 10 feet (3.3 the University of Utah named a birdlike preda- meters) long and weighing some 200 pounds, over- tory dinosaur Hagryphus giganteus on the basis powering a large, living prey animal such as a had- of hand and foot bones found in the Kaiparowits rosaur or ceratopsian dinosaur. Formation (Zanno and Sampson 2005). As dino- The ornithomimids were incredibly successful in saurs go, Hagryphus was a relatively small animal the late Cretaceous. Their remains have been found (about 10 feet [3.3 meters] long) but was one of the all over North America and throughout much of largest North American members of a specialized Asia in sediments of roughly the same age as the group of theropods known as the oviraptorosaurs. The Late Cretaceous 203

7.35. Reconstruction of Hagry- phus giganteus from the Kaip- arowits Formation of southern Utah. Scale bar = 3 inches (1 m).

Oviraptorosaurs are best known from Asia, where it to scurry through the dense Late Cretaceous for- many different species have been identified in late ests with ease and agility. Like its oviraptorosaur rel- Cretaceous rocks. These odd predators have short atives to the north, it may have been an omnivore, skulls that terminate in a parrotlike toothless beak. using its dexterous hands to capture small prey such The skulls of some oviraptorosaurs were decorated as lizards, frogs, birds, and mammals. But Hagry- by prominent bony crests, while in others the skulls phus was substantial larger (probably about 30–40 were smooth. The skulls were lightened by several percent heavier) than any of its known North Amer- relatively large openings in the bone of the lower ican relatives. and upper jaws. Strong evidence indicates that the Talos bodies of Asian oviraptorosaurs were feathered, and As birdlike as Ornithomimus and Hagryphus may their overall skeleton is very birdlike. In fact ovi- have been, another dinosaur predator recently dis- raptorosaurs are placed in the clade Maniraptora, covered from the Kaiparowits Formation may be an which includes the most birdlike theropod dino- even closer relative of the modern hawks and eagles. saurs as well as the living birds. While the ornitho- In 2011 Talos sampsoni was named by paleontolo- mimids are related to birds, the oviraptorosaurs are gists on the basis of a partial skeleton discovered in even more birdlike and therefore are considered to 2008 from the Kaiparowits outcrops in the GSENM be part of the evolutionary lineage leading to mod- (Zanno and others 2011). Talos was a troodontid ern birds. theropod, a group of relatively small but highly spe- Though the skull and most of the skeleton of cialized predators known primarily from Asia that Hagryphus are unknown, its hands and feet are had a number of striking birdlike characteristics. clearly those of an oviraptorosaur, with long fingers, The troodontids had very lightly constructed skel- tipped with prominent curving claws, and muscu- etons, with thin-walled bones, long legs, and short lar forelimbs. While it is not certain that Hagryphus forelimbs. The skulls of the troodontids were very had a bony crest on its skull, this feature is fairly delicate, with large, forward-directed eyes and a rel- common among oviraptorosaurs in Asia. Ovirapto- atively large brain case. The ear region of the skull rosaurs are also known from Montana and Alberta, was very specialized in most troodontids, suggest- where Chirostenotes is one of the most abundant ing that their keen stereo vision was coupled with and best known. A general idea of the appearance acute hearing. Overall the troodontids appear to of Hagryphus can be formulated based on this ovi- have been small, swift, and brainy little predators. raptorosaur (fig. 7.35). Hagryphus was a stealthy ani- Though only a portion of the skeleton of Talos mal, which possessed strong hind limbs for swift is known from the GSENM (fig. 7.36), the pre- running and a relatively short tail that would allow served bones suggest that it was a speedy and 204 Chapter 7

7.36. Reconstruction of the skeleton of Talos sampsoni, with the known portions of the skeleton in red. Total length of the skeleton is about 6 feet. From Zanno and others 2011.

7.37. Foot of Talos samp- mechanical leverage and swift running. This small soni from the Kaiparow- dinosaur was only about 3 feet (1 meter) high, with its Formation of southern Utah. DI–DIV indicate the a body perhaps twice as long, and weighed an esti- toes, while the bones of the mated 80 pounds (Zanno and others 2011). The mid-foot (metatarsals) are preferred prey of Talos was no doubt the smaller labeled MTI–MTIV. Scale creatures that Ornithomimus and Hagryphus also bar = approximately 0.5 inch (10 mm). From Zanno dined on but may have included insects, small birds, and others 2011. and reptile hatchlings located with its sharp vision and keen hearing. Avisaurus: Bird or Dinosaur? In 1985 a portion of a small birdlike theropod foot found in the Late Cretaceous sediments of Montana was named Avisaurus archibaldi, and a new family was proposed to accommodate the new genus (Brett-Surman and Paul 1985). The specimen is only about 3 inches (7.5 cm) long and consists of three metatarsals (middle foot bones), fused together toward the proximal (upper) end (fig. 7.38). This fossil exhibits several features that are unusual in Late Cretaceous theropods, including a middle metatarsal (III) that is not concealed or pinched between the other two, a prominent bump on the second metatarsal, and a very thin fourth metatarsal. These features are similar to those com- 7.38. The middle foot of Avisaurus. Similar bones from monly seen in some (but not all) bird fossils from the Kaiparowits Formation suggest that this animal was the late Cretaceous. As is often the case when such a medium-sized perching bird, not a dinosaur. Scale bar limited fossil material is used to establish a new = 1 inch (2.5 cm). After Brett-Surman and Paul 1985. genus (not to mention a whole new family), paleontologists have vigorously debated the nature and stealthy predator like other troodontids. The feet validity of Avisaurus. Is it a bird, a dinosaur, or and hind limbs (fig. 7.37) were highly elongated as in something in between? If it is a dinosaur, then how other birdlike dinosaurs, an adaptation for greater is it related to other birdlike theropods of the Late The Late Cretaceous 205

Cretaceous? What were its habits? What ecological Daspletosaurus and Gorgosaurus, close kin to the niche did it fill? infamous predator Tyrannosaurus. In New Mexico The Avisaurus controversy came to Utah in an equally imposing tyrannosaurid known as Bis- 1993 when a much more complete specimen was tahieversor was recently described from sediments described from the Kaiparowits Formation (Hutchi- that accumulated at the same time as those in the son 1993). The Kaiparowits specimen was disar- GSENM area (Carr and Williamson 2010). These ticulated and incomplete, but enough of it was large and terrifying predators are all related in the recovered to determine that Avisaurus had a deep family Tyrannosauridae and must have been one of keel on its sternum, a well-developed furcula (the the most fearsome sights in nature 75 million years “wishbone”), specialized wing-supporting hands ago in North America. with sharp claws, and caudal vertebrae compressed The identity of the large theropods that inhab- into a birdlike structure known as a pygostyle ited the Kaiparowits coastal plain was a mystery (Hutchison 1993). The Kaiparowits specimen clearly until very recently. Isolated and fragmentary fos- demonstrates that Avisaurus is a bird, probably sils of the large predators had been recovered, but related to the land birds known as the enantiorni- they were too scrappy or insufficiently diagnostic to thines that flourished on several different continents allow them to be clearly associated with any known during the Late Cretaceous. genus and species from adjacent regions. All that Avisaurus was a good flier but evidently lacked could be established was that something similar to the endurance of modern birds. It probably spent the monstrous predators of New Mexico, Montana, a great deal of time on the ground or perching in and Alberta terrorized the smaller prey animals in trees, flying only when necessary to escape pred- southwest Utah during the time when the Kaip- ators or to catch prey. We assume that Avisaurus arowits sediments were deposited. In 2011 scientists was a predator, but it may have been a scaveng- established the identity of at least one of the large ing bird similar to a vulture or an omnivore like a tyrannosaurids as Teratophoneus curriei, based on raven. Unfortunately, no one knows what the skull disarticulated skull bones found in the Kaiparowits of Avisaurus was like because this part of the skele- Formation in the GSENM. Teratophoneus was noth- ton has never been found. Someday the rocks of the ing like the small birdlike dinosaur predators that Kaiparowits Formation may yield additional fos- lived in southern Utah. It was a menacing beast that sils that will allow us to gain a better understand- deserves its name: the “monstrous murderer” of the ing of this interesting bird. One thing is certain, Kaiparowits coastal plain. however: given the prevalence of birdlike dinosaurs Teratophoneus was identified on the basis of sev- such as Ornithomimus, Hagryphus, and Talos, along eral bones of the skull and a few elements of the with primitive birds such as Avisaurus, the forested skeleton (fig. 7.39). The recovered bones clearly floodplains and bayous of southern Utah were gar- establish this predator as a member of the fam- nished with feathers in the Late Cretaceous. ily Tyrannosauridae, though the details of its skel- Teratophoneus eton remain mostly unknown. It appears that the All of the dinosaur predators from the Kaip- skull of Teratophoneus was a bit shorter and box- arowits Formation described thus far are relatively ier than the skulls of Tyrannosaurus and Alberto- small animals. Most of them probably weighed 100 saurus and probably had fewer teeth. Teratophoneus pounds or less when full grown. To the north, in was smaller than Tyrannosaurus, with a body about Montana and Alberta, sediments of the same age 20 feet (about 7 meters) long that weighed about a as the Kaiparowits Formation have produced the ton. The larger tyrannosaurs of North America were remains of large and fearsome predators such as nearly twice the size of Teratophoneus. The fossil 206 Chapter 7

suggests that other large tyrannosaurid predators may have been prowling the southern Utah coastal plain. Some frightening hunters stalked and terrorized the herbivorous dinosaurs and smaller animals living in Utah’s prehistoric jungles. But the largest and most menacing predator of them all may not even have been a dinosaur. Lurking in the rivers and ponds of the Kaiparowits coastal plain was something even more frightening than Teratophoneus. Deinosuchus In 2007 paleontologists discovered a partial skull and armor plates of what was probably the larg- 7.39. Skull bones from Teratophoneus curriei, with the outline of the entire skull indicated by the dashed line. est predator of the Kaiparowits ecosystem (Titus Scale bar = 20 inches (50 cm). Redrawn from Carr and and others 2008). These remains belonged to a truly others 2011. gigantic crocodilian known previously from several late Cretaceous localities in North America as material used to define Teratophoneus may have Deinosuchus. Though only a portion of the skele- been the remains of a subadult individual, so per- ton was preserved in the Kaiparowits Formation at haps a full-grown specimen might have been larger. the GSENM site, the skull bones clearly belonged to Though most of the postcranial skeleton of Ter- this large crocodile, best known from fossil material atophoneus is unknown, the overall similarities found in Texas. It is hard to overstate the enormity between its skull and those of other tyrannosaurids of this gigantic crocodile: Deinosuchus possessed a suggest that it shared the reduced forelimbs, mas- skull more than 6 feet (2 meters) long attached to a sive hind limbs, and a long stiff tail common in this body more than 30 feet (10 meters) long (fig. 7.40). family of theropods. The large, serrated, and robust Along the massive upper and lower jaws were some teeth were clearly designed to shred flesh and crush eighty robust teeth, most of which were 2 inches bones, a feeding habit that is probably characteris- (5 centimeters) or more in diameter. The posterior tic of all tyrannosaurids. Even though it was smaller teeth of Deinosuchus are low and knobby, while the than some of its tyrannosaur relatives, Teratopho- teeth in front tend to be larger and more sharply neus was still the largest theropod known from pointed. These teeth appear to have been designed the Kaiparowits Formation and no doubt created to seize large and struggling prey animals with panic among the herds of hadrosaurs whenever it the snout and crush their bones and/or protective appeared on the scene in the late Cretaceous. armor in the back of the mouth. In addition to Teratophoneus, fossil material cur- The broadened tail and stubby limbs of Deinosu- rently emerging from the Kaiparowits Formation chus indicate that it was a primarily aquatic animal,

7.40. Body outline of the enormous crocodile Deinosuchus known from the Kaiparowits Formation, compared with an average-sized human. Vertical scale bar = 3 feet (1 m); horizontal scale bar = 16 feet (5 m). The Late Cretaceous 207 as are most of its much smaller living relatives. The rivers, swamps, and lakes of the Kaiparowits coastal plain probably contained a variety of prey animals for these large crocodiles. Fish were almost certainly a part of the Deinosuchus diet, but such a large animal was probably not restricted to eating relatively small fish. Isolated turtle bones and some partial skeletons are relatively abundant in the Kaip- arowits Formation. As many as six different kinds of turtles may have lived in the Kaiparowits rivers and ponds (Sampson, Gates, and others 2010). The teeth of Deinosuchus could easily have crushed the shells of even the largest of them. Most intriguing, though, is the strong possibility that Deinosuchus may also have preyed on dinosaurs, using ambush tactics similar to the way in which modern crocodiles seize large prey animals that venture too close to the water’s edge. Considering that dinosaurs in the Kaiparowits ecosystem were so abundant and 7.41. Paleogeography of the Western Interior Seaway varied, a large aquatic predator like Deinosuchus and Laramidia during late Campanian time, showing the distribution of ceratopsian dinosaurs. From Sampson, would have many opportunities to attack whenever Loewen, and others 2010. these animals came to the water to drink or crossed streams during migrations. With a body more than plain that extended north well into what is now 30 feet (10 meters) long and weighing some 5 tons Canada and Montana (fig. 7.41). To the east of this or more, Deinosuchus could have overpowered coastal plain the Western interior Seaway separated most of the dinosaurs that it might have ambushed America into an eastern land mass and western one from the water. Not even the fearsome Teratopho- known as Laramidia. Late Cretaceous dinosaurs neus would have been safe from the enormous jaws are known from the eastern United States, but our and powerful body of Deinosuchus, launching itself knowledge of the overall dinosaur fauna in that area from the shallow water toward an unsuspecting vic- is limited by the low abundance of fossils from areas tim. What an amazing sight the struggle between an on the east side of the Western Interior Seaway. On attacking Deinosuchus and a dinosaur victim would the west side of the seaway, where sediment derived have been: tons of reptilian flesh twisting and turn- from the uplands of Laramidia accumulated contin- ing in the water, frantic bellows and screams of the uously during the late Cretaceous, we have a much doomed prey, and a frenzied stampede of other ani- better record of the dinosaur communities that lived mals from the riverbank to the safety of the sur- on the broad coastal plain. Abundant dinosaur fos- rounding forest. sils of late Campanian age have been collected for more than a century in Alberta, Montana, Wyo- The Kaiparowits Fauna Province ming, New Mexico, and Colorado. We can now add We learned earlier that during the time recorded southern Utah to the list of the most notable Cam- by the sediments of the Kaiparowits Formation (late panian dinosaur localities in North America due the Campanian age of the Cretaceous period) south- recent and ongoing discoveries made in and around central Utah was situated along a broad coastal the Grand Staircase–Escalante National Monument. 208 Chapter 7

Collectively the Campanian vertebrate fauna It is still not clear what kept the dinosaurs liv- of Utah was a varied and highly diverse array of ing on the northern and southern parts of the animals that included hadrosaurs, ceratopsians, Laramidia coastal plain separate. No geological evi- ankylosaurs, ornithomimids, oviraptorosaurs, dence indicates the presence of a topographic bar- troodontids, tyrannosaurs, turtles, crocodiles, liz- rier that could have isolated the two dinosaur ards, birds, and small mammals. The dinosaurs in populations. It is reasonable, however, that the cli- this assemblage are in aggregate much different mate of the two regions may have been signifi- from the array of nodosaurs, sauropods, dromaeo- cantly different, given the far northern latitude of saurs, therizinosaurs, and carnosaurs that pre- the coastal plain in Montana and Alberta. Perhaps ceded them in the early Cretaceous. The distinction a cooler climate in the north resulted in a distinc- between the early Cretaceous and late Cretaceous tive flora that favored feeding adaptations for dino- dinosaur faunas is probably the reflection of at least saur herbivores that would be less successful to the two factors: (1) the shift to more swampy condi- south, where different plants were available. The tions in the late Cretaceous as the Western Interior pattern, timing, and severity of seasons would also Seaway encroached from the east, and (2) the pro- have been as different in the late Cretaceous as they gressive evolution within the various dinosaur (and are today in Alberta and Utah. Other factors, such bird) lineages. as the terrain, availability of water, or currents in the Though we will certainly discover additional Western Interior Seaway, might have induced addi- late Campanian dinosaurs in Utah in the com- tional environmental differences between the north ing years, the fauna of this time is now known well and south coastal plains. Scientists have recently enough to allow some comparison between it and linked the patterns of evolution in ceratopsian and contemporary arrays of dinosaurs that lived on the hadrosaurian dinosaurs to the changes in land- same coastal plain farther north in Montana, Wyo- scapes that accompanied mountain building in ming, and Alberta. Several paleontological stud- Campanian and later times (Gates and others 2012). ies have suggested that the Utah assemblage of late Whatever caused the endemism of dinosaur com- Campanian dinosaurs was unique and consisted munities, it remains evident that the dinosaurs liv- of many species that were endemic to the southern ing in southern Utah during the late Campanian age coastal plain of Laramidia (Lehman 2001; Sampson, were a distinctive array that evolved in response to Loewen, and others 2010; Gates and others 2010). conditions unique to the local habitat and environ- The ceratopsian dinosaurs are one of the groups ment. We still have much to learn about the patterns that best show this north-south endemism. Differ- of distribution and the evolutionary history of the ent species of large herbivorous dinosaurs lived on beasts of the bayous. the northern coastal plain of Montana and Alberta About 70 million years ago, during the ter- than those that dwelled to the south in Utah and minal age of the Cretaceous known as the Maas- New Mexico (Sampson, Loewen, and others 2010; trichtian, renewed geological activity in the Sevier fig. 7.41). Kosmoceratops and Utahceratops from the Orogenic Belt coupled with new disturbances far- Kaiparowits had ceratopsian relatives to north; but ther east began to affect the landscapes of central they belonged to different species, and there was and eastern Utah. The uplift that began at this time evidently little intermingling between the two com- ultimately led to the complete withdrawal or regres- munities. Other dinosaurs such as the hadrosaurids sion of the Western Interior Seaway from Utah. (Fricke and others 2009) also show this north-south The sea drained away into Colorado and Wyoming, endemism and restricted patterns of distribution on and the coastal environment—the broad flood- the coastal plain of Laramidia. plains, the swamps, the lagoons, the bays, and the The Late Cretaceous 209 bayous—vanished with it. The rising land in and or became extinct. Thus a new chapter in the story of near Utah induced climatic changes affecting the Utah dinosaurs began in Maastrichtian or latest Cre- land, even as the geological remodeling was in prog- taceous time. It was unlike any of the preceding epi- ress. Life responded to these changes, as it always sodes in this remarkable pageant of Mesozoic life, has. New plant communities developed in response however: this was the final act of a 140-million-year to the changing conditions, and new types of ani- natural drama. At the end of Maastrichtian time the mals appeared to replace those that either migrated dinosaurs disappeared—completely and forever. Chapter 8 The Curtain Falls 08The Dinosaurs of the North Horn Formation The final sliver of Mesozoic time, the last gasp of CENOZOICOld Quaternary the dinosaurs, is known as the Maastrichtian age “Quarternary” sub-era Period of the Cretaceous period. The Maastrichtian began 2.6 m.y. approximately 70 million years ago and ended about 65 million years ago. Its end coincides with the closing of the last period of the Mesozoic, the Neogene Period Cretaceous, and the beginning of the first period

of the Cenozoic, the Paleogene. Over the past sev- Old 23 m.y. “Tertiary” eral decades the formal subdivisions of the Ceno- sub-era

zoic era have undergone substantial revision by ERA the International Commission on Stratigraphy. Paleogene Older terms such as “Quaternary” and “Tertiary” Period have been redefined as informal suberas of Ceno- zoic time, and new period names such as the Paleo- 65 m.y. gene and the Neogene were formally defined (fig. 8.1). The reasons for these revisions are a bit tech- Cretaceous Period nical and beyond the scope of this study of Utah 8.1. Subdivisions of the Cenozoic era. The last 65 million dinosaurs, but they were established to remedy years of geological time are the Paleogene, Neogene, some long-standing problems and uncertainties and Quaternary periods. in the way Cenozoic time was subdivided. What is relevant to our quest is that many of these revi- time, we will use that abbreviation to designate the sions of the Cenozoic time scale were formalized boundary between the Mesozoic and Cenozoic eras, as recently as 2009. Some of the older terms par- even though K-Pg is more consistent with the cur- ticularly the “Tertiary” (as the earliest “period” of rent terminology used by geologists. the Cenozoic) still linger in both older literature Once the Maastrichtian age of the Cretaceous and current discussion. The transition from Meso- period was over, the dinosaurs vanished completely. zoic to Cenozoic time is traditionally known as the No dinosaur fossils, except for some probably K-T interval (“K” = Cretaceous; “T” = the old “Ter- reworked scraps, have ever been found in sediments tiary”), named for the periods that embrace it. Tech- of early Paleogene age. Because the Maastrichtian nically the transition should now be identified as represents the last episode in such a grand story of the K-Pg (Cretaceous-Paleogene) interval, and sev- vertebrate evolution, its deposits have been intensely eral recent studies have begun to use that designa- studied on a global scale. Wherever the K-T bound- tion (e.g., Belcher 2009). Because “K-T” is so firmly ary is recorded in the rock record, geologists and entrenched in the literature and popular discussion paleontologists have swarmed like a pack of hun- of the events that accompanied the end of Mesozoic gry raptors, searching for clues to the mystery of

210 The Curtain Falls 211 the extinction of the dinosaurs and the events that occurred during their final days. From Italy to Den- mark, from Spain to Montana, from New Mexico to Antarctica, and even in deposits from the deep ocean floor, scientists have scrutinized the K-T transition in great detail. Collectively they have documented the shifts in the fossil fauna and flora, analyzed the changes in sediment type and chemistry, and established the timing of the great transition with uncommon if not perfect precision. The K-T interval is without doubt one of the most ardently studied phases in the 4.6 billion–year history of our planet. Yet we still have no universally accepted explanation for what caused the end of the era of dinosaurs. To be sure, many hypotheses on the extinction of the dinosaurs have been proposed. But the data from the K-T interval, despite their prodigious volume, are still not sufficient to “prove” any one of the hypotheses to the satisfaction of all scientists. We will return to the issue of dinosaur 8.2. Paleogeography of the Utah region at the beginning extinction later in this chapter, but first let’s examine of the Maastrichtian age of the late Cretaceous. Recon- the K-T sediments in Utah and get acquainted with struction from Ronald Blakey/Colorado Plateau Geosys- the last dinosaurs to live in the Beehive State. tems, Inc. Used with permission.

end. As the swamps and bayous declined, the prime The K-T Boundary in Utah dinosaur habitat diminished as well. The hadro- Unlike some of the earlier phases of dinosaur his- saur-ceratopsian dinosaur community could no lon- tory, Utah localities have not provided a wealth of ger thrive in Utah without swampy forests, at least information on the K-T transition. There is a good to the degree that it had during the Campanian age. for reason this: during the Maastrichtian most of To the north, in Wyoming, Montana, and Alberta, the Utah landscape was in the midst of geologi- where swampy coastal conditions persisted into the cal changes that did not favor either the continuous Maastrichtian, this assemblage of dinosaurs contin- deposition of sediment or the preservation of dino- ued to flourish and diversify until the very end of saur fossils. By the beginning of Maastrichtian time the Cretaceous. the great Western Interior Seaway had regressed Perhaps the Maastrichtian dinosaur communities far to the east and north. The former coastal low- of this northern region included the descendants of lands of central Utah were now far inland from the Utah emigrants that migrated north, tracking the shrinking seaway, which had withdrawn to Colo- habitats to which they were so well adapted. When rado, Wyoming, and adjacent regions (fig. 8.2). The the seaside swamps withdrew from Utah, many great swamps dried out as water drained toward the of the dinosaurs evidently followed them east and distant, receding sea. Much of the lush vegetation north. The regression of the Western Interior Sea- that cloaked the former coastal plain withered, and way in North America was not a local phenome- the great era of coal deposition in Utah came to an non: similar widespread regressions were occurring 212 Chapter 8 at the same time on a global scale. Dry land had appeared everywhere in the world in continental lowlands that were formerly submerged by the great inland seas. By the end of the Maastrichtian the distribution of land and sea began to look similar, though still not identical, to the pattern that we see in the modern world. As the great regressions modified the patterns of land and sea, changes in climate were initiated on both the global and local scales (Royer 2006). Far from the moderating effects of the withdrawn sea, the climate in Utah probably became a little less humid and also possibly cooler. This climatic shift is just one of the many profound environmental changes that began near the end of the Cretaceous. In Utah the draining of the swamps linked to the regression of the sea was accelerated by at least two important geological disturbances. In fact 70 million years ago, as Maastrichtian time was just beginning, Utah landscapes experienced what was 8.3. Paleogeography of the Utah region at the end of the probably the most significant period of upheaval Maastrichtian age of the late Cretaceous. The mountainous Sevier Orogeny Belt stood some 10,000 feet high, of the entire Mesozoic. The Sevier Orogenic Belt in while the early stages of the Laramide Orogeny were western Utah was in its final stages of deformation elevating areas to the east. Reconstruction from Ron- and went out with a bang! The last pulse of uplift ald Blakey/Colorado Plateau Geosystems, Inc. Used with in the Sevier belt in Utah created the structures permission. now known as the Gunnison thrust system in central Utah and the Absaroka thrust system in north- to heave upward. The ascent of these areas east of ern Utah (Wiltschko and Dorr 1983; DeCelles and the Sevier Belt was subtle at first but accelerated others 1995; DeCelles and Coogan 2006). In addi- steadily throughout latest Cretaceous to early Paleo- tion to initiating these thrust faults, the intensi- gene time. This uplift signified the beginning of fied compressive forces of early Maastrichtian time the Laramide Orogeny, the widespread episode of also reactivated some of the older thrusts and crum- mountain building that ultimately raised the mod- pled rock layers into large folds (Talling and others ern Rocky Mountains. After its beginning in the 1995). This early Maastrichtian deformation elevated latest Cretaceous, Laramide deformation contin- the mountainous Sevier Orogenic Belt one last time, ued across the Rocky Mountain region for at least to heights of about 10,000 feet, and invigorated the 30 million years, well into the Eocene epoch of the rivers that drained east into the foreland basin. Paleogene period. Even as the earth was shaking from the pow- The Sevier Orogeny and the Laramide Orog- erful forces that thrust the Sevier belt skyward, eny are generally separated in both time and space new disturbances began to affect the land farther throughout the Rocky Mountain–Great Basin east during the Maastrichtian age. The land sur- region. The Sevier Orogeny primarily affected face in the Uinta Mountains, the San Rafael Region, the eastern Great Basin region from Late Jurassic and the Circle Cliffs area near Capitol Reef began through Cretaceous time. The Laramide Orogeny The Curtain Falls 213 followed the Sevier disturbance, affecting the Rocky These factors make it difficult to locate the “golden Mountain area to the east during the latest Creta- spike” that separates Cretaceous strata from Tertiary ceous and early Cenozoic (Paleocene and Eocene deposits in most Utah rock successions that span epochs). In central Utah, however, the final stages the Mesozoic-Cenozoic boundary. No sediment at of the Sevier Orogeny and the beginning of the all was deposited in many places at this time, and Laramide Orogeny overlap both temporally and only unconformities mark the threshold of the geographically. The overlap of these two orogenies Cenozoic. In other localities we can only approxi- was most conspicuous during Maastrichtian time. mate the position of the boundary in the complex, Uplift in the Sevier belt accompanied mountain- unconformity-ridden, and sparsely fossiliferous suc- building related to the beginning of the Laramide cessions of conglomerate, sandstone, and mudstone. Orogeny across a broad area of central Utah, from Elsewhere in the Rocky Mountain region, with the Wasatch-Uinta Mountains area to the high pla- less geological chaos in progress, the K-T bound- teaus in the southwest corner of the state. The net ary is less difficult to locate (but still not always effect of this geological ruckus was to transform the easy). This is the case in New Mexico, Wyoming, Sevier foreland basin of the earlier Cretaceous into a and Montana. It comes as no surprise that much of complicated terrain consisting of many rising uplifts the research on the K-T transition has focused on separated by relatively small interior basins by the rocks exposed in those areas. But recent research end of Maastrichtian time (fig. 8.3). has suggested that the K-T boundary is preserved The rock record of these events is a rather com- within at least three Utah rock sequences: the North plicated heap of conglomerates shed from the ris- Horn Formation of central Utah (Difley and Ekdale ing uplifts (both Sevier and Laramide), sandstones 2002a, 2002b; Difley and others 2004), the Canaan deposited by rivers flowing into the evolving inte- Peak and Grapevine Wash Formations of southwest rior basins, and fine-grained siltstone and mudstone Utah (Fillmore 1991; Schmidt and others 1991), the that accumulated on floodplains and lake bottoms. Evanston Formation of the Wasatch-Uinta Moun- In the uplifted areas, such as the San Rafael Swell tains region (Mullens 1971; Ryer 1976), and perhaps and the Uinta Mountain regions, the K-T transition a few other less thoroughly studied rock units. Of is marked only by unconformities as rock was worn these rock sequences, only the North Horn Forma- away from the rising land surfaces. It was only in tion has produced more than a few scraps of fossil the interior basins that developed east of the Sevier bone. To glimpse the Maastrichtian dinosaur fauna Belt and between the ascending Laramide struc- of Utah, scientists have looked primarily to the tures that sediment was deposited more or less con- exposures of the North Horn Formation on the high tinuously during the K-T interval. Even the interior Wasatch Plateau of central Utah. These rocks are basins experienced periodic times of erosion or our only source of abundant fossil material docu- nondeposition that created small unconformities menting the last participants in the 140-million-year in the basin-filling rock sequences (Fouch and oth- cavalcade of Utah dinosaurs. ers 1983; Hintze 1988; Goldstrand and others 1993). In addition, the strata that record the K-T transition The North Horn Formation in Utah are not always fossiliferous and commonly lack minerals that can be radiometrically dated. The The North Horn Formation was named for expo- K-T boundary is most clearly expressed by the dis- sures on North Horn Mountain, not far from Joe’s tinct fossil assemblages before and after the fau- Valley on the Wasatch Plateau of central Utah nal transition, so it is next to impossible to locate (Spieker and Reeside 1925; Spieker 1946). In this the precise K-T boundary without abundant fossils. area the North Horn Formation consists of about 214 Chapter 8

1,500 feet of soft red and gray siltstone and mudstone interlayered with less abundant sandstone and limestone. In the Wasatch Plateau region the North Horn Formation rests on the underlying Price River Formation (of the Mesaverde Group), the last strata deposited in the Sevier Foreland basin prior to its disruption during the Laramide Orogeny. In the San Pitch Mountains west of the Wasatch Pla- teau the North Horn Formation is over 3,000 feet thick and contains thick sandstone units and great wedge-shaped masses of conglomerate along with finer-grained sediments typical of the exposures on the Wasatch Plateau (Talling and others 1995). Core samples from oil wells in the western Uinta Basin indicate that the North Horn Formation extends in the subsurface north from the Wasatch Plateau into 8.4. The North Horn Formation basin, 65 to 70 mil- that area, where it is up to 2,500 feet thick. To the lion years ago. The elongated interior basin was situ- south the North Horn Formation can be traced at ated between the Sevier Orogenic Belt to the west and least to the Capitol Reef National Park area, beyond the San Rafael Swell and Circle Cliffs uplifts to the east. which it becomes buried under younger volcanic Rivers drained into the basin from both directions. rocks that cover the Boulder Mountains and other high plateaus. Sediments typical of the North Horn the Maastrichtian. Maastrichtian sediments accu- interval cannot be recognized in the Bryce Can- mulated elsewhere in Utah in other small basins yon region. The K-T boundary in the southern area located between the Sevier and Laramide Uplifts, lies within the Canaan Peak Formation, which con- but these deposits either were later eroded or are sists almost entirely of massive pebble and boulder nonfossiliferous. conglomerate. The Canaan Peak rubble probably The sediments of the North Horn Formation represents the coarse sediments flushed from high- were deposited by streams that drained the uplands lands around the southern end of the interior basin adjacent to the basin and in lakes that formed from in which the North Horn sediments accumulated. the water impounded within the enclosed lowland The North Horn Formation has not been identi- (Lawton 1986; Olsen 1995). Conglomerates in the fied east of the San Rafael Swell or in western Utah. North Horn Formation around the periphery of the The known extent of the North Horn Formation basin suggest swift rivers flowing across steep allu- thus defines an elongated basin of sediment accu- vial aprons that descended toward the lower part mulation that stretched diagonally through central of the basin. In the middle of the basin the rivers Utah (fig. 8.4; Franczyk and Pitman 1991; Franczyk became more sluggish and deposited finer sand in and others 1992). This interior basin was some 130 the channels and spread mud and silt across the miles long as it ran along parallel to and just east basin floor during flood events. The silty limestone of the Sevier Orogenic Belt, from the Uinta Moun- layers of the North Horn Formation record the peri- tains to the southern High Plateaus. The North odic development of ponds and lakes, some quite Horn basin was only about 40 miles wide, bounded large, in the central portion of the basin. The pres- on the east by the San Rafael Swell and Circle Cliffs ence of many fragmentary fossils of fish similar to Uplift, both of which were actively rising during gar pikes as well as fossils of turtles and crocodiles The Curtain Falls 215 verifies the ubiquity of aquatic habitats in the North Horn basin. In addition, fossils of freshwater clams and snails are abundant in many parts of the North Horn Formation, particularly in the lake-deposited limestones. For reasons that are not yet clear, plant macrofossils are not especially abundant in the North Horn Formation, but thin coal seams in these strata suggest that reasonably lush vegetation grew across the basin floor, at least at certain times in certain places. The terrestrial environment of central Utah during the K-T transition was probably a well-watered lowland, nestled between rugged mountains to the west and hilly uplands to the east, north, and south. The basin floor was dotted with lakes and ponds, especially during the rainy seasons. Isolated clumps of vegetation developed wherever water was sufficient to support trees and shrubs. The climate of the Maastrichtian–early Tertiary appears to have been warm and temperate to subtropical (Robison 1986). Lizard fossils, including some spectacularly well-preserved specimens, are quite abundant in the North Horn Formation (Gilmore 1942a, 1942b, 1943). Among the lizards, the 3-foot-long (1-meter) 8.5. Polyglyphanodon, a large herbivorous lizard from herbivore Polyglyphanodon was particularly com- the North Horn Formation of Utah. This genus was rep- mon (fig. 8.5). At least four different species of resented by more than a dozen articulated skeletons turtles are also known from the North Horn For- similar to the one shown in the sketch. Scale bar= 1 inch (25 mm). Based on a photograph from Gilmore 1942b. mation, including the large tortoiselike Basilemys (Gilmore 1946). The abundance of reptiles supports the concept of generally warm climatic conditions parts of the North Horn Formation (Olsen 1995) during the time represented by the North Horn For- provides additional evidence for dry periods during mation. Impressions of palm fronds in the dino- the time represented by these sediments. saur-bearing part of the North Horn Formation Soon after the North Horn Formation was first (Zawiskie 1983) are also consistent with warm, sub- described, it attracted the attention of paleontolo- tropical conditions in the Maastrichtian floodplains gists because the lower portions of the formation of central Utah. Traces and casts of plant roots in contain many dinosaur fossils and the upper part soils preserved in the North Horn sediments indi- produces abundant remains of a diverse mammal cate that some of the shrubs possessed long “tap fauna. Dinosaur remains disappear from the rock roots,” suggesting a low or fluctuating water table succession above the lower beds and do not occur (Bracken and Picard 1984). This in turn indicates with the mammal fossils found in the upper part that the climate of the Maastrichtian in central Utah of the formation. Moreover, mammal fossils from may have been strongly seasonal. The presence of the upper North Horn Formation, such as Oxyclae- nodular caliche and red-colored soil horizons in nus, Promioclaenus, and many others, indicate a 216 Chapter 8

found in the lower beds (deposited during the final portion of Maastrichtian time) reveal a fauna much different from anything that preceded it.

Dinosaurs of the North Horn Formation

Dinosaur remains were first reported from the North Horn Formation from the Wasatch Plateau in the late 1930s and 1940s (Gilmore 1938, 1946; Spieker 1946), after a series of paleontological expeditions to the area by the Smithsonian Institution beginning in 1937. During the Smithsonian expeditions of the late 1930s interest was directed primarily toward the Paleocene mammal remains in the upper part of the formation (Gazin 1938, 1939, 1941). The mam-

8.6. Paleocene mammal fossils from the North Horn For- mal fossils and the stratigraphy of the rocks they mation: A. a portion of the jaw of Oxyclaenus pugnax, are found in have continued to attract a great deal about 0.75 inch long; B. molar tooth of Promioclaenus of interest in more recent years (Tomida and But- acotylus, about 0.125 inch tall. These small mammals ler 1980; Robison 1986; as well as others). Until very are among dozens of genera that indicate an early Ceno- zoic age for the upper part of the North Horn Formation. recently few additional dinosaur fossils had been Based on photographs from Robison 1986. discovered from the North Horn Formation since these early paleontological explorations. Jensen Paleocene age, which was the earliest epoch of the (1966) described eggshell fragments from the for- Paleogene period (fig. 8.6; Gazin 1938, 1939, 1941; mation that were attributed to dinosaurs, but little Archibald and others 1983; Robison 1986). So the else surfaced until the late 1990s, when several new distribution of dinosaur and mammal fossils in fossil-producing localities were reported (Difley and the North Horn Formation suggests that the K-T Ekdale 1999; Sampson and Loewen 2005). Though boundary lies somewhere in the middle of this thick we still have much to learn about Utah’s last dino- rock succession. The pattern of magnetic field rever- saurs, and the search for additional clues continues sals recorded in the sediments of the North Horn every summer high on the Wasatch Plateau, pale- Formation reveals that it spans the interval about ontologists are beginning to glimpse an intriguing 74–51 million years ago (Talling and others 1994, array of creatures that populated the North Horn 1995). These dates confirm that the K-T bound- basin immediately before the K-T extinction event. ary, which occurred about 65 million years ago, Alamosaurus is recorded somewhere in the middle of this rock The best-represented dinosaur in the North Horn sequence. In 2004 scientists from Brigham Young Formation is the sauropod Alamosaurus sanjuanen- University finally succeeded in precisely identify- sis, first identified from Maastrichtian deposits near ing the K-T boundary in the North Horn Formation Ojo Alamo, New Mexico, by C. W. Gilmore in 1922 about 625 feet above the base of the formation on (Gilmore 1922, 1946). During the Smithsonian expe- the basis of a shift in the plant species represented ditions many Alamosaurus fossils were excavated by fossil pollen (Difley and others 2004). For dino- from the North Horn Formation, including thirty saur enthusiasts, the North Horn Formation is an articulated caudal vertebrae (representing nearly all especially intriguing rock unit because the remains of the tail), twenty-five chevron bones, portions of The Curtain Falls 217 the pelvis and shoulder, an almost complete fore- the sauropods seem to have had a nasty habit of los- limb, and large sternal plates. Even though the skull, ing their heads soon after they died. Alamosaurus is neck, main portion of the backbone, and most of merely one of many “headless” sauropods. Like the the limbs were missing, the North Horn specimen others Alamosaurus was certainly a browsing her- is still one of the best ever found for Alamosaurus. bivore, but whether it fed on low growing shrubs or In terms of its overall appearance, Alamosaurus was tall trees remains unclear. probably similar to the sauropods of the late Juras- The caudal vertebrae of Alamosaurus are very sic but was not as large as some of them. Its forelimb distinctive, which is fortunate for paleontologists was about 9–10 feet (3–3.3 meters) long and its total studying the North Horn specimen, with a nearly length probably not much more than about 35 feet complete series of tail bones. The first caudal ver- (about 11 meters). The long forelimb, with an elon- tebra, located at the base of the tail immediately gated humerus, suggests a posture reminiscent of behind the rump, was of biconvex form (rounded Brachiosaurus, in which the shoulders were higher on both ends). All other caudal vertebrae have a than the hips. Alamosaurus also seems to have been ball-like knob on the rear surface and a deep socket a heavy-bodied sauropod, however, perhaps some- on the front end (fig. 8.7). Vertebrae with such ball- what like the husky Camarasaurus from the Juras- and-socket joints, with the socket facing forward, sic. In particular the sternal plates (or “breast bones”) were massive and heavy. Along with the robust forelimb bones, this suggests that the Utah Alamosaurus probably had bulky limbs and shoulders, had an overall stocky build, and may have weighed in at 25–30 tons. Recent discoveries of substantially larger Alamosaurus bones in New Mex- ico have suggested that this sauropod could have attained a body exceeding 65 tons, making it one of the largest dinosaurs known (Fowler and Sullivan 2011). No one knows what the neck of Alamosau- rus was like, but the hefty proportions of its skeleton suggest that it might have been relatively short and thick. Although Alamosaurus was of modest size compared to the sauropod giants of the Jurassic, it was clearly the largest dinosaur of its time in North America. No other Maastrichtian dinosaur, including the fearsome Tyrannosaurus rex, came close to matching its bulk. No skull of Alamosaurus has ever been discov- 8.7. Alamosaurus caudal vertebrae (from right to left): 1, ered, but a few fragmentary teeth have been found 2, and 3 from the North Horn Formation of central Utah in association with bones of this genus in New Mex- in lateral view (top) and anterior view (bottom). Note the ico (Kues and others 1980). The teeth are small and biconvex form of the first caudal vertebra (upper right) cylindrical, similar in a general way to the peg- and the hollow sockets on the front ends of the second and third vertebrae. The upward projecting neural like teeth of Diplodocus. In the absence of a skull we spines are situated on the forward half of the main body cannot be certain about the placement of the nos- (or centrum) of each vertebrae. Scale bar = 6 inches (15 trils or other details of the head. As we have seen, cm). Based on photographs from Gilmore 1946. 218 Chapter 8 are described by the term “procoelous.” In addi- less common hypsilophodonts, nodosaurs, and early tion, the caudal vertebrae of Alamosaurus have neu- ceratopsians. For at least 30 million years, until late ral spines that are consistently located on the front Maastrichtian time, no sauropods appear to have half of the main portion of the bone (centrum). lived anywhere in North America. This interval has Another unique feature of Alamosaurus is the com- been called the “sauropod hiatus” (Lucas and Hunt plete absence of the deep pockets (pleurocoels) on 1989). Some paleontologists (e.g., Mannion and the sides of the vertebral centra. The pleurocoels are Upchurch 2011) have attributed this apparent disap- variously developed in other sauropods, but they all pearance of sauropods to the uneven preservation have them. Among the sauropods, procoelous cau- and discovery of coastal (as opposed to inland) sau- dal vertebrae (lacking pleurocoels) with anteriorly ropod dinosaurs. If so, it is puzzling that the non- placed neural spines are very peculiar features that sauropod dinosaurs do not show the same sampling in part characterize the family Titanosauridae of the discrepancy during the sauropod hiatus. In any suborder Sauropodamorpha. Even though much event the occurrence of Alamosaurus in the North of the anatomy of Alamosaurus is still unknown, Horn Formation is significant because it signals the the caudal vertebrae of the North Horn speci- reappearance of the sauropods in the fossil record of men clearly indicate that this sauropod belongs to North America after a lengthy absence. This absence the Titanosauridae, a family of dinosaurs not pres- may be due to sampling inadequacies or may reflect ent in North America prior to the Maastrichtian. It a local extinction followed by the reintroduction of is interesting that a new family of sauropods sud- sauropods millions of years later. denly appears in North America at the time when It is even more interesting that Alamosaurus the North Horn sediments were deposited, but the appears at about the same time in New Mexico intrigue grows if we consider the broader patterns (Gilmore 1922; Lozinsky and others 1984), Texas of sauropod history on this continent. (Lucas and Hunt 1989), Wyoming (Lucas 1981), We have seen that the late Jurassic was the and Utah. Thus the sauropods reenter the fossil “Golden Age of Sauropods” in North America, a record of North America after the hiatus in strata time when these gigantic herbivores were the dom- of nearly identical age in several different places in inant plant-eaters. In early Cretaceous time the sau- the Southwest. This pattern suggests that Alamo- ropods declined dramatically, perhaps as a result saurus either evolved in or migrated into Maas- of climatic variations, evolutionary changes among trichtian habitats that had previously excluded the plants, and competition from rapidly evolv- sauropods. Furthermore, no sauropod remains are ing ornithischians such as nodosaurs and ornitho- known from the rich Maastrichtian bone beds of pods. Only a few sauropods, such as Pleurocoelus, Alberta and Montana, suggesting that Alamosaurus Venenosaurus, and Cedarosaurus, seem to have never spread north of Wyoming. Assuming that the been widespread and relatively common in North simultaneous appearance of Alamosaurus bones in America during the early Cretaceous. About 95 the latest Cretaceous strata of the Southwest marks million years ago, just as the last half of the Creta- the reappearance of sauropods in portions of North ceous began, the sauropods appear to have suffered America, some obvious questions emerge. Did the a striking reduction in numbers and diversity in Maastrichtian sauropods “reevolve” there from North America. No sauropod fossils have ever been some other ancestor? Did they migrate to North found anywhere in North America in rocks equiva- America, and if so from where? What caused the lent in age to the Mesaverde Group of Utah. Instead disappearance of sauropods after the early Cre- the large herbivore niche was evidently filled dur- taceous? What factors led to their return in the ing this time by the hadrosaurs, accompanied by Maastrichtian? The Curtain Falls 219

8.8. An Alamosaurus herd moves along the edge of a large late Cretaceous lake in central Utah. Illustration by Carel Brest van Kempen.

Most paleontologists agree that Alamosau- Argentinosaurus, Futalognkosaurus, and Puertasau- rus most probably returned to North America by rus. Elsewhere in the Southern Hemisphere late Cre- migrating north from South America, where titano- taceous titanosaurids are also known from India, saurid sauropods were common, over a land con- Egypt, Malawi, Australia, Madagascar, and Laos nection between the two continents (Bonaparte (McIntosh 1990; Calvo and others 2007). Several dif- 1984; Lucas and Hunt 1989). This explains the con- ferent titanosaurids are even known from Europe. centration of Alamosaurus in the Southwest and In fact the titanosaurids were one of the most abun- its absence in the northern part of North Amer- dant and successful groups of dinosaurs in the world ica. The view of Alamosaurus as an immigrant from during their time, though they were concentrated the south also makes sense because the titanosau- mainly on the southern continents. The only barrier rids were widespread and abundant in the Southern to the dispersal of the South American titanosaurids Hemisphere during the sauropod hiatus that affected was the ocean that completely surrounded that con- North America. Titanosaurid remains are found in tinent for much of the Cretaceous. To spread beyond late Cretaceous strata in Brazil, Uruguay, Chile, and South America, all the titanosaurids needed was a Argentina and include some very large forms such as land bridge to facilitate their northern exodus. And 220 Chapter 8 that is exactly what developed in late Mesozoic time, Sauropods in North America, they were gone com- in the form of a volcanic arc that joined the two land pletely and forever. Taking this line of thought one masses of North and South America (Anderson and step further, if the sauropod hiatus signifies a wide- Schmidt 1983). spread sauropod extinction in western North Amer- Even though we often hear that North America ica, then what caused it? What factors led to the and South America became joined only a few mil- extinction of the Jurassic sauropods and what con- lion years ago, the modern connection is just the ditions permitted an ecologically similar animal most recent union between the Americas. After the to thrive later in the Maastrichtian age? Perhaps late Mesozoic connection was established and Ala- it was the changing climate, as mentioned previ- mosaurus scampered north over it, North and South ously. Maybe the comings and goings of sauropods America became separated again until very late in in North America had something to do with the the Cenozoic, when the current isthmus of Cen- advances and retreats of the continental seas. Con- tral America developed. This scenario suggests ceivably it might be related to the changing com- that the dinosaurs that ended the sauropod hia- position of the global flora or the advent of the tus in North America were not descendants of the hadrosaurs and ceratopsians. No one knows the sauropods known from the Morrison Formation answers to these questions for sure. The sauropod or Cedar Mountain Formation. We already know hiatus remains an unexplained phenomenon. Thus that, of course, because Alamosaurus is a titanosau- Alamosaurus may not be the best known of Utah’s rid, not a diplodocid, camarasaurid, or brachiosau- many dinosaurs, but it is still one of the most fasci- rid. Although its general appearance may have been nating elements of the Maastrichtian fauna. We still similar to Camarasaurus, Alamosaurus (fig. 8.8) was have much to learn about it and about the circum- not the evolutionary progeny of any North Ameri- stances surrounding its appearance in the North can dinosaur that preceded it. That is why the skel- Horn Formation. etal features of Alamosaurus seem so distinctive in comparison to the more familiar late Jurassic sauro- Torosaurus/Triceratops pods of Utah. Alamosaurus evolved from different Along with Alamosaurus, the remains of at least ancestors, in a different place, and under different eleven individual ceratopsian dinosaurs were found ecological conditions. in the North Horn Formation during expeditions The well-established view of Alamosaurus as an conducted by the Smithsonian Institution (Gilmore alien invader from South America spawns an inter- 1946). Because it has been so commonly featured in esting perception of the sauropod hiatus and pro- movies, books, and toys, the most familiar ceratop- vokes a bewitching question. If Alamosaurus is sian to most people is the quadrupedal herbivore not a descendant of the Jurassic sauropods of the Triceratops (“three horn face”), with two prominent North America, then the disappearance of these brow horns, an upward curving nose horn, and a giant herbivores that initiated the sauropod hiatus broad frill extending over the neck from the back of was not just an out-migration but a genuine drop- the skull. These features are all typical of the Cera- dead extinction. If Alamosaurus was derived from topsia, but many other distinctive traits define this a diplodocid (for example) ancestor, we could envi- clade (or infraorder) of ornithischian dinosaurs. sion that this sauropod lineage persisted in South Unique to the ceratopsians is a beaklike bone, the America (or somewhere else?) and was reintro- rostral, which joins the premaxilla at the tip of the duced to Utah in the Maastrichtian. But this is not snout (fig. 8.9). The surface of the rostrum is wrin- the case. When the brachiosaurids, camarasaurids, kled and rough, indicating that a horny sheath cov- and diplodocids vanished after the Golden Age of ered the bone in life. The snout of ceratopsians The Curtain Falls 221

8.10. The teeth of ceratopsian dinosaurs were arranged in vertical rows (left, seen in cross-sectional view) that 8.9. Skulls of Torosaurus and Triceratops: Torosaurus were formerly locked together in the jaw (right). The (top), known from the North Horn Formation of Utah, hard enamel surfaces joined to form a continuous blade- has a long perforated frill, well-developed brow horns, like cutting edge along the upper and lower jaws. and a small nose. The smaller Triceratops (bottom) had a more circular and solid frill and shorter, more robust horn that curved forward. Scale bar = 8 inches (20 cm). grinding motion that the hadrosaurs employed in Modified from sketches of Dodson and Currie 1990. processing their plant fodder. To envision the effect of the different ways of was tipped with a vicious, sharp-edged beak that chewing in these two groups of ornithischians, would have been extremely effective in chopping think of the hadrosaurs swallowing a mashed pulp vegetation. Except for the closely related psittaco- of plant matter while the ceratopsians filled their saurs, no other group of dinosaurs possessed such gullets with material more like confetti. Hence the a parrotlike snout. The teeth of ceratopsians were ceratopsians appear to have been well adapted to arranged in vertical rows similar to the tooth bat- processing tough or fibrous vegetation, while the teries of the hadrosaurs (fig. 8.10), but they func- hadrosaurs might have preferred softer food. Cer- tioned in a unique manner. The tooth rows were tainly the Maastrichtian fossil record, rich in both locked together to form a continuous cutting blade ceratopsians and hadrosaurs, indicates that these along the edge of the jaws. The upper teeth passed two ornithischians were perfectly compatible with just outside of the lower teeth each time the mas- each other. sive jaws were closed by powerful muscles anchored The fragmentary ceratopsian fossils described near the back of the head and on the frill (fig. 7.21). by Gilmore (1946) from the North Horn Formation As the hard enamel edges of the teeth sheared past were originally identified as Arrhinoceratops? uta- each other, vegetation was chopped into small hensis. Arrhinoceratops is known from the Maas- pieces. Coupled with the beak at the snout, ceratop- trichtian deposits of Alberta but is otherwise quite sian jaws were no doubt capable of chopping even rare in North America (Tyson 1981). Arrhinoceratops the toughest vegetation in the manner described in means “without nose horn face,” in reference to the chapter 7. This is much different from the transverse relatively small horn (actually a mere bump) on the 222 Chapter 8 nose of this genus. Lawson (1976) invalidated Gilm- These differences in the skull and frill of Torosau- ore’s queried identification and, on the basis of the rus and Triceratops led paleontologists to consider shape and sculpturing of the frill bones, determined them two separate but related genera of ceratop- that the North Horn material represented a species sians for more than a century. Scientists from Mon- of Torosaurus (“bull reptile”). But the Utah material tana State University (Scannella and Horner 2010), was unique compared to other fossils of Torosaurus, however, noticed an interesting trend while study- which are found primarily in Montana, Wyoming, ing more than thirty Montana Triceratops skulls and South Dakota. So Lawson (1976) combined representing various growth stages. As individu- Gilmore’s original species name with the correct als of Triceratops aged, their skulls became larger genus name to designate the Utah specimen as Toro- and began to develop some of the features that saurus utahensis. A recent reappraisal of Torosaurus were originally used to distinguish this genus from (Scannella and Horner 2010) has suggested that the Torosaurus. The frill of Triceratops becomes pro- specimens on which this genus is based are actually portionally longer and openings develop in the the remains of large individuals of Triceratops. We parietal bones as the animals grow and mature. will explore this uncertainty in a little more detail Thus the head and frill of a large full-grown Tricer- later in this chapter. atops would look strikingly different from the skull Torosaurus is known only from the skull, but of a younger subadult. Observing how similar the it appears to have been one of the largest ceratop- skulls of Triceratops became to those of Torosau- sians ever identified. The skull of some specimens is rus in later developmental (or “ontogenetic”) stages, over 9 feet (3 meters) long. Using the better-known the researchers concluded that Triceratops and Toro- but generally smaller Triceratops as a model for the saurus represent younger and older growth stages, postcranial skeleton, full-grown Torosaurus indi- respectively, of the same dinosaur. So should the viduals might have been about 25 feet (8 meters) ceratopsians from the North Horn Formation of long and weighed 10–15 tons. Torosaurus had a long, Utah now be referred to as Triceratops? Unfortu- heart-shaped frill extending back from the skull at nately, there is an additional complexity to consider. a rather low angle, completely covering the neck Three species of Torosaurus have been described: and shoulders. The frill was actually longer than T. latus, the “northern” species known from Maas- the main portion of the skull and had two open- trichtian strata from Wyoming to Alberta; T. gla- ings separated by a bar of bone that formed a ridge dius, a somewhat larger individual with subtle running fore and aft along the midline (fig. 8.9). differences in the shape of the frill among other The outer edge of the frill was smooth and unorna- things; and T. utahensis, the North Horn species, mented. The morphology of the frill of Torosaurus which also occurs in New Mexico and Texas. The is different from that of the more familiar Tricer- differences among the three species have mainly to atops, which had a relatively small, solid frill with a do with the size and shape of horns and frills. The knobby border formed by small bones known as the species of Torosaurus that was synonymized with epoccipitals. The two brow horns of Torosaurus pro- Triceratops by the recent revision was T. latus. T. jected upward at a high angle from just behind the utahensis was different in the details and propor- eyes and curved gently toward the snout at their tips tions of the skull bones. Therefore the possibility (Lawson 1976). The nose horn was a small, blunt still exists that Torosaurus utahensis remains a valid cone that was positioned above and just behind the genus and species and is distinct from Triceratops nostrils. Like other ceratopsians Torosaurus had a that lived farther to the north. In resolving the ques- prominent beak formed by a horny sheath that cov- tion of whether or not T. utahensis is a unique cer- ered the curved rostral bone at the tip of the snout. atopsian, it is appropriate to consider the function 8.11. A herd of Torosaurus (Triceratops?) feeding along a wash descending into a distant lake. Illustration by Carel Brest van Kempen. 224 Chapter 8 and variability of the frills and horns of ceratopsian hunters have developed complicated formulas to dinosaurs. “score” them. So it is likely that at least some of the The ornate frills of ceratopsians were probably features by which the various genera and species of used in ritualistic displays and in sparring for mates. ceratopsians are recognized really represent male The bone that composes the frills was generally and female or old and young individuals of the same too thin (and perforated in some species) to have species. For example, the sixteen different species of afforded any significant protection from late Creta- Triceratops that have been described by paleontolo- ceous predators. Recall also that good evidence indi- gists probably represent morphological variations of cates that the ceratopsians were herding animals (fig. no more than two species, T. horridus and T. pror- 8.11). Communication between individuals is essen- sus (Ostrom and Wellnhofer 1990; Forster 1996). tial in animals that depend on a herd for protection Without more complete fossil material represent- and successful reproduction. It seems reasonable ing Torosaurus utahensis, we cannot be absolutely to envision the frills as devices for signaling species certain that it represents a species of Triceratops or membership and gender, establishing a position in the remains of a different ceratopsian. For now we the social hierarchy of the herd, and attracting mates. will retain the name Torosaurus for the North Horn The frills may also have been important in anchoring specimens but consider this dinosaur to be very the powerful jaw muscles and increasing the leverage similar and closely related to Triceratops. with which they operated the lower jaw. The mus- Alamosaurus and Torosaurus are the only herbiv- cle-attachment functions of the frill were probably of orous dinosaurs from the North Horn Formation secondary importance, however, a fringe benefit of that can be identified to the genus level, but other such an expanded skull (with apologies for the obvi- plant-eaters lived in Utah during the late Maastrich- ous pun). The large frills of ceratopsians would have tian. Gilmore (1946) reported a hadrosaur femur been very effective in communicating with members along with a few isolated skull bones that evidently of the herd. By tipping the snout or waving the head, belonged to a ceratopsian that was distinct from ceratopsians could have sent visual signals to other Torosaurus. No identifiable hadrosaur material has members of the herd that would have been hard to been reported from the North Horn Formation miss. The highly ornamented edge of the frills in since Gilmore’s expeditions, so it is still uncertain some genera, coupled with possible patterns of color what genus is represented by the femur. Footprints in the skin covering the frill, might have increased of herbivorous dinosaurs are also fairly common the visibility of the display. in the North Horn Formation (Difley and Ekdale In most herding animals the males engage in 2002b) but cannot be associated with any specific nonlethal competition with one another for dom- genus. The size and density of footprints in many inance and reproductive opportunities. This was track-bearing horizons in the North Horn Forma- probably the primary function of the horns in cer- tion do, however, suggest that dense herds of some atopsian dinosaurs, just as it is in the case of many large animals periodically gathered in central Utah modern herding mammals such as bison and elk. If during Maastrichtian time. Jensen (1966) described the horns and frills of ceratopsians evolved for com- several different types of fossil eggshells from the munication, display, and mating purposes, then it is lower portion of the North Horn formation and almost certain that the size and shape of these struc- attributed some of them to dinosaurs, but he could tures varied with age and gender, just as they do in not identify the egg-layers to the genus or species all horned or antlered mammals of today’s world. level because no embryos were preserved with the The antlers of male deer, elk, moose, and other shell fragments. Fossil eggshell fragments are very game animals are so variable in form that trophy common in the lower, dinosaur-bearing, portion of The Curtain Falls 225 the North Horn Formation even to this day. Given the abundance of lizard and turtle remains in the North Horn, though, it is likely that many of these eggs were laid by nondinosaur reptiles or perhaps even by birds. Reconstructions of the eggs based on the shell fragments preserved in the North Horn Formation, however, suggest that some of the eggs were too large to have been laid by the reptiles or turtles known from fossil bones (Jensen 1966). These larger eggs might have been of dinosaurian origin but cannot be associated with any particular taxon. Until an intact egg is found with an identifi- 8.12. A generalized Tyrannosaurus rex skull, show- able embryo preserved inside, we can’t be sure about ing the position of the postorbital (diagonal ruling) and squamosal (horizontal ruling) bones that were pre- the identity of the egg-layers. Currently the eggs served in the specimen from the North Horn Formation. prove only that reptilian (or avian) reproduction The skull of T. rex could exceed 5 feet in length in large was occurring in the North Horn basin. individuals.

Tyrannosaurus rex: Menace of the Maastrichtian are incomplete, representing only about 17 per- The latest Cretaceous theropods in Utah were cent of the skeleton. But these preserved elements a complete mystery until recent years. Except for include some bones of the skull (fig. 8.12) that are several isolated teeth, a large hand claw, and a both diagnostic of and nearly identical to those of foot bone (Gilmore 1946), no fossils from thero- more complete Tyrannosaurus skulls from Mon- pod dinosaurs had been formally reported from tana. In particular the shape and size of the postor- the North Horn Formation. The fossils reported by bital and squamosal bones near the rear of the skull Gilmore are too scrappy to be identified with preci- of the Utah specimen clearly identify it as Tyran- sion, but they do indicate that some large dinosaur nosaurus. The North Horn tyrannosaur appears to predators accompanied Alamosaurus, Torosaurus, have been a large individual, perhaps 30–35 feet (10– and the hadrosaurs during late Maastrichtian time. 12 meters) long, with a body weight of some 6–7 A few additional teeth, all isolated and fragmentary, tons. Though the jaws are not preserved, the dagger- had surfaced since Gilmore’s time from the North like teeth of this enormous predator were probably Horn Formation and age-equivalent strata. These more than 6 inches (15 centimeters) long and curved fragmentary remains suggested that large theropods toward the rear to impale and dismember struggling similar to Tyrannosaurus and Albertosaurus, the prey animals. Many of the isolated fragments of the- most terrifying of all theropods, prowled the North ropod teeth known from the North Horn Formation Horn basin. Fieldwork in the North Horn Forma- may have originated in the jaws of this bloodcur- tion over the past decade conducted by researchers dling predator. and students from the University of Utah and Col- Tyrannosaurus rex was widely distributed in lege of Eastern Utah led to the discovery of a partial western North America during the Maastrich- skeleton of the most fearsome predator of the entire tian age, ranging from Alberta to Texas. Most of Mesozoic era: Tyrannosaurus rex (Sampson and the thirty or so Tyrannosaurus skeletons discovered Loewen 2005). thus far, however, were found in the sediments of The skeletal remains that document the presence the coastal plains adjacent to the shrinking western of Tyrannosaurus rex in the North Horn Formation interior seaway. The Utah specimen from the North 226 Chapter 8

Horn Formation is very unusual in that the bones have been positively identified or are presumed to were preserved in sediments that accumulated in an have been present in the North Horn Formation. interior basin surrounded by mountainous uplands. In addition to central Utah, the Alamosaurus fauna Thus it appears that Tyrannosaurus was a generalist has also occured in the late Maastrichtian sediments predator with broad ecological and environmental of New Mexico, west Texas, and southwest Wyo- tolerances. It probably also utilized several differ- ming (Lehman 1987). This unique congregation of ent types of prey, including some of the larger dino- late Maastrichtian dinosaurs appears to have been saurs that occupied the interior basin habitat along confined to the interior basins of southwest North with it. In this regard it is interesting to note that the America. North Horn tyrannosaur remains are found in the Farther north, in central Wyoming, eastern Mon- same part of this thick formation that produces the tana, the Dakotas, and Alberta, the Triceratops fauna bones of Alamosaurus. Though we have no direct has been recognized in rocks equivalent in age to fossil evidence of Tyrannosaurus preying on Ala- the North Horn Formation. This fauna is dominated mosaurus, encounters between the two are certainly by Triceratops, a ceratopsian absent from the Ala- plausible given the co-occurrence of their fossils in mosaurus fauna of Utah (if we assume that Toro- same strata. Imagine the commotion that we might saurus utahensis is a valid genus and species), along have witnessed when the largest and most advanced with hadrosaurs, the thick-skulled pachycephalo- land predator that ever lived met one of the most saurs, ankylosaurs, and large theropods. The Tric- massive sauropods of the entire Mesozoic era at the eratops fauna evidently was adapted to low coastal edge of a lake or along a riverbed in central Utah: an environments quite dissimilar to the interior basin uproar bordering on pandemonium! in which the North Horn Formation was deposited and where the Alamosaurus fauna flourished. Late Cretaceous Faunal Provinces Finally, the Leptoceratops fauna, character- Because the North Horn Formation and other ized by the diminutive protoceratopsian for which late Maastrichtian strata of western North Amer- it is named, represents an upland assemblage that ica produce the remains of the very last dinosaurs, includes many of the same taxa as the Triceratops the fossil assemblages from these rock units have fauna, albeit in somewhat different proportions. The been of great interest to paleontologists. A wealth Leptoceratops fauna is known only from a few locali- of Maastrichtian dinosaur fossils has been collected ties in northwest Wyoming and Alberta, where hilly in many different localities in the West, from New highlands existed during the late Maastrichtian. Mexico to Alberta. This material has allowed the The last herbivorous dinosaurs to live in North recognition of three distinctive late Maastrichtian America were thus dispersed in recurring assem- dinosaur faunas based mostly on the types of her- blages that correspond to specific environments: the bivores present (Lehman 1987). The North Horn Alamosaurus fauna in the interior basins, the Tricer- Formation produces what is known as the Alamo- atops fauna along the coastal lowlands, and the Lep- saurus fauna, named for the largest dinosaur repre- toceratops fauna in the interior uplands (Lehman sented in it. In addition to the namesake genus, this 1987). The predatory theropods, particularly the fauna contains Torosaurus utahensis and the hadro- larger forms such as Tyrannosaurus, do not seem to saurs Edmontosaurus and Kritosaurus (both “hold- have had such restricted distribution and were evi- overs” from the slightly older Campanian fauna). dently equally effective in preying upon the different The theropods in this fauna are less restricted to it communities of herbivores. This biogeographic pat- but include Tyrannosaurus and Albertosaurus. All tern is not really very surprising, because we would of the dinosaurs of the Alamosaurus fauna either expect to see a similar pattern among any group of The Curtain Falls 227 animals distributed over such a broad and environ- of the past, they were more successful than any mentally varied region. We certainly have little dif- group of land animals in earth history. The dino- ficulty recognizing the unique mammal faunas that saurs survived, indeed thrived, during several peri- exist in moist coastal lowlands, high alpine for- ods of environmental change that might have ended ests, semiarid grasslands, and deserts in modern the ecological reign of less resilient creatures. Even North America. For example, we don’t expect to see with our attention restricted to Utah alone, we have a moose in a Louisiana bayou or a mountain goat in seen that several different faunas of dinosaurs came the prairies of Nebraska. Some overlap among the and went throughout the Mesozoic, as geological modern mammal faunas exists, of course, and it is forces wrought changes in the land and the environ- usually most notable among the predators. Coyotes ment. The ability of the dinosaurs to adapt success- and mountain lions, for example, can survive almost fully to new conditions, and to do so for more than anywhere—in swamps, in blistering deserts, in 140 million years, is clearly demonstrated by the high mountains, not to mention the dry hills above Mesozoic fossil record of Utah. On a global scale the smoggy Los Angeles. In a similar way the dinosaur evolutionary versatility and endurance of dinosaurs predators of the Maastrichtian age such as Tyranno- is even more impressive. Thus it is not their phy- saurus and Albertosaurus appear to have been pres- letic death that should mesmerize us but rather their ent almost everywhere, but the herbivores appear extraordinary ability to survive so long as mon- to have been more restricted in consistent faunal archs of the terrestrial ecosystem. The dinosaurs are assemblages adapted to specific environmental con- amazing not for the way they died but for the ways ditions. Similar biogeographic patterns probably they lived. existed throughout the Mesozoic for all the dino- Still, it is only natural to ponder the circum- saurs on every continent, but the extraordinarily stances that finally ended the rule of the dinosaurs. rich fossil record of the late Maastrichtian of North What events could have happened, what changes America affords a rare opportunity to discern the could have occurred, that exceeded the proven abil- faunal groupings. Many more dinosaur fossils will ities of the dinosaurs to adapt and survive? In view have to be collected from older rocks before we can of their prior success in the face of profound envi- formulate equally precise ideas about the biogeog- ronmental changes, the extinction of the dinosaurs raphy of dinosaurs during the earlier periods of the is more than just a casual curiosity: it is a puz- Mesozoic. zling enigma. Consequently every person interested in dinosaurs, whether they are paleontologists or not, eventually is drawn to consider the extinc- Extinction: The Enduring Mystery tion issue. It seems that almost everyone develops or The fact that the dinosaurs ultimately became subscribes to a theory on the matter. The scientific extinct is one of the most intriguing aspects of their literature dealing with topics related to the extinc- existence in the Mesozoic era. Many people, scien- tion of the dinosaurs is an enormous body of infor- tists and nonscientists alike, have become preoccu- mation. Just listing the references would require a pied by the disappearance of this group of reptiles tome as long as this book. In fact such bibliogra- and with attempts to understand their so-called fail- phies have been compiled and are indeed book- ure some 65 million years ago. Personally I view it sized (see Fouty 1987). Good summaries of the somewhat differently: I see their remarkable success dinosaur extinction debate are included in D. A. during most of the Mesozoic as the most fascinating Russell and G. Rice (1982), M. J. Benton (1990), element in the story of the dinosaurs. Despite the and J. D. Archibald (1996). As these reviews dem- perception of dinosaurs as obsolete biological relics onstrate, scores of theories have been proposed to 228 Chapter 8 account for the extinction of the dinosaurs. Some terminal Cretaceous phenomena as the widespread of the theories, such as the one concerning alien regression of the seas, a volcanic outburst, numer- beings from space, are so easily dismissed or are ous mountain-building events, changing patterns of so utterly untestable as to be laughable. Many oth- global geography, and climatic trends are not simple ers summon plausible causes of extinction such to assess. These factors may have operated to varying as disease, asteroid impacts, geographic and cli- degrees in different locations at different times, fur- matic change, changes in plant communities, repro- ther complicating the task of evaluating their over- ductive dysfunction, and dwindling gene pools. all global effect. Individually none of these events is Each can find at least some support in the geologi- an adequate explanation for the demise of the dino- cal and paleontological data that can be brought to saurs; but when considered together in terms of bear on the issue. But even now, in the early twenty- their complex interactions, they might have trig- first century, we have no single explanation for the gered the K-T biotic transition. In the modern world demise of the dinosaurs that is universally accepted it is sometimes difficult to distinguish a sole cause by a majority of scientists. For example, contrast the for the decline of a single endangered species, so you views recently expressed in P. Schulte and others can imagine how perplexing it might be to formu- (2010) that the dinosaurs died out as a consequence late a model for the disappearance of many differ- of an asteroid impact with the viewpoint expressed ent creatures 65 million years ago. It is unreasonable in the rebuttal by J. D. Archibald and others (2010) to expect that such a complex biological phenome- that attributed the extinction to multiple causes. non would have a single simple cause. It seems that Our inability to gain a complete understand- modern human beings are reluctant to embrace ing of the extinction of the dinosaurs after so much complexity and uncertainty in many fields. We tend intense study stems, I think, from several fac- to champion solutions similar to those advocated tors. First, though extinction is a natural and ongo- by politicians in television sound bites: simple, easy ing biological process, it is never as simple as many answers that make sense on the surface but ulti- people assume. The death of an individual organ- mately break down when tested against reality. The ism is much different from the death of an entire extinction of the dinosaurs was a complex event that species, genus, or family. Remember that when the in all probability had complex causes. dinosaurs vanished, two orders of reptiles disap- A second reason for the difficulty is that the geo- peared forever. The search for a “killing mechanism” logical record of the extinction of the dinosaurs is has sometimes centered on events that might cause really not very good. This is unquestionably the case the death of individual dinosaurs in some locality at in Utah, where a single formation (the North Horn) some time, but it is unclear how such mechanisms provides only meager information on the great K-T could have led to the extinction of larger taxonomic transition. This situation is certainly not unique to groups dispersed over a broad area. Extinctions in Utah. In fact most of what we know about the pace general are complex events in the history of life that and detailed pattern of dinosaur extinction comes result from the combined effects of numerous fac- from the study of the K-T sediments in the east- tors. The search for a “smoking gun” for the dino- ern Montana region, specifically the dinosaur-bear- saur extinction has often focused on identifying ing late Maastrichtian Hell Creek Formation and the event that led to the faunal turnover. In all like- the overlying Paleocene Tullock Formation (Dod- lihood the biotic stress that tipped the ecological son and Tatarinov 1990). Elsewhere in the world, scales against the dinosaurs at the end of the Creta- as in Utah, the sediments that span the K-T transi- ceous period had several different causes. The com- tion usually lack adequate numbers of dinosaur fos- bined ecological effects of such well-documented sils, are complicated by unconformities, or are too The Curtain Falls 229 imprecisely dated to tell us much about the event(s) the originators of the asteroid hypothesis; nor was of the time. Even in the case of the Hell Creek For- it central to the arguments in favor of this explana- mation scientists have formed different interpre- tion articulated more recently by Schulte and others tations about the timing of the extinction and the (2010). Not surprisingly, the rebuttal of the asteroid pattern of dinosaur abundance and diversity (e.g., impact hypothesis by Archibald and others (2010) Sheehan and others 1991 vs. Sloan and others 1986). emphasized that not one of the forty-one authors of The imperfections of the geological record of the the paper by Schulte and others (2010) was a spe- dinosaur extinction pose a very real challenge to cialist in the fossil record of dinosaurs or related our attempts to understand this event. This is one vertebrates. In actuality the paleontological record reason why so many theories have been formulated (imperfect, remember?) can be interpreted as either and why it is not always possible simply to choose supporting the scenario of asteroid impact or con- between them. In many cases the imperfect data tradicting it (see the references listed in the bibliog- offer equivocal support for several different inter- raphy). pretations and extinction scenarios. Thus the long debate between the “impactors” A third problem in the search for an explana- and the “nonimpactors,” which persists to this day, tion of the K-T extinctions is that the mystery has is influenced by which data (paleontological or become so attractive that specialists from many dif- geochemical) are emphasized in drawing conclu- ferent scientific disciplines have directed their atten- sions. Geochemists recognized the evidence for a tion to it. In the long run this is a good situation profound event at the K-T boundary but had little because it may reveal new insights that might ulti- understanding of the pace and timing of dino- mately lead us a sound understanding of the event. saur extinction. Paleontologists, exercising their In the short term, however, we can expect addi- traditional bias toward fossils, were more famil- tional confusion as specialists familiar with only one iar with the pattern of declining dinosaur diversity aspect of the problem develop explanations for their and might envision a different extinction mech- data while ignoring the perspectives of other disci- anism on that basis. Rather than being adversar- plines through either design or innocent nescience. ies, paleontologists and geochemists are actually The recent and much-debated theory that the allies, because each brings unique perspectives to dinosaur extinction was caused by an asteroid the study of dinosaur extinction. Paleontologists impact offers a good example of this point. The the- would probably never have discovered the irid- ory emerged when concentrations of the rare ele- ium anomaly and might have remained ignorant of ment iridium were discovered in K-T sediments in the very good evidence for an explosive event at the Italy and (subsequently) many other places in the end of Cretaceous without the involvement of sci- world (Alvarez and others 1980; Prinn and Feg- entists from other disciplines. So, while multidis- ley 1987). For good scientific reasons the iridium ciplinary approaches to solving the mysteries of concentration was considered to be the result of nature can result in new perspectives and are gener- an impact between the earth and an extraterres- ally good, it might take some time before solutions trial body, a 6-mile-wide asteroid, by the geolo- that satisfy all of the available data are developed. gists and chemists who discovered it. The extinction Scientists from a broad spectrum of specializations of the dinosaurs, which occurred at approximately currently are working to reconcile the paleontolog- the same time when the iridium-rich marine clay ical, geological, astronomical, and chemical data was deposited, was attributed to the impact. The that pertain to the K-T extinctions. No universally actual paleontological record of dinosaurs in late acceptable answers have yet emerged: the extinction Maastrichtian time, however, was not studied by 230 Chapter 8 of the dinosaurs is as great a mystery now as it was Because of these highly selective impacts, the decades ago. overall severity of the K-T extinctions is difficult to In spite of the confusion and uncertainty, scien- assess because it depends on what taxonomic level tists generally agree on a few points regarding the and which groups of organisms we choose to ana- K-T extinctions. First, it was not just the dinosaurs lyze. The primary victims (dinosaurs and other large that disappeared. Many other groups of organisms reptiles) were such striking creatures that the sever- experienced extinction, or a severe decline in abun- ity of the K-T extinctions often has been overstated. dance or diversity, at about the same time when For example, it is frequently alleged that the K-T the last of the dinosaurs vanished. The demise of extinctions claimed about 75 percent of all life (spe- the dinosaurs was just a part (albeit the most nota- cies) on the earth (e.g., Allaby and Lovelock 1983; ble part) of a broader episode of extinction that Raup 1986; Glen 1990). An analysis of more than seems to have been of global extent. Among the one hundred species of terrestrial and aquatic ver- most prominent nondinosaur victims of the K-T tebrates from the K-T boundary sequence in Mon- extinctions were the pterosaurs, ichthyosaurs, ple- tana, however, indicates that 64 percent of them siosaurs, marsupial mammals, coiled ammonites, survived and only 36 percent became extinct several groups of bivalve molluscs, and plankton (Archibald 1991). Among families of fish, only that secreted tiny calcareous shells. Many other eleven out of eighty-five (13 percent) became extinct groups of animals not only survived the K-T events during the K-T transition (Benton 1989). Other but appear to have flourished during this time of studies suggest a similarly modest extinction for all presumed biotic stress. The survivors include the groups of organisms on a global scale (Briggs 1995). crocodiles and turtles, amphibians such as frogs The K-T extinctions, usually described as a “mass and salamanders, many lizards, small placental extinction,” may not have been that massive after all. mammals, birds, bony fish, sharks, and plankton Even among the dinosaurs, our principal interest in that possessed siliceous shells. Mysteriously, many this tangled debate, we should remember that most of the survivors were living in the same or similar of the dinosaurs that ever lived on the earth became habitats occupied by the victims of the K-T extinc- extinct long before the end of the Cretaceous. As tions. The undisputed selectivity of the K-T extinc- seen in earlier chapters, several dinosaur extinctions is the most difficult conundrum we face in tions occurred during the Mesozoic, each eliminat- understanding how the extinctions occurred. What ing some genera from the faunas that existed at the happened to remove so many species of calcare- time. In each case except the K-T event, the survi- ous plankton in the sea but leave those with silica vors diversified again following the extinction to shells unaffected? What events destroyed the pop- give rise to new faunal assemblages. ulations of carnivorous marine reptiles but did not Dinosaur extinctions of varying severity can create unfavorable conditions for the sharks and be documented at the end of the Triassic, after the other predatory fish? What caused the flying and early Jurassic, just before the late Cretaceous, and of gliding pterosaurs to vanish but allowed the birds course at the end of the Cretaceous (the K-T extinc- that fluttered beside them to flourish? Why did the tions). While more than 350 dinosaur genera are dinosaurs disappear from the swamps of Utah and known, only a few such as Triceratops, Torosau- Montana while the crocodiles and turtles in the rus, Tyrannosaurus, Alamosaurus, and Edmonto- same bogs thrived? It is extremely difficult to rec- saurus died out during the K-T extinctions. All the oncile the selectivity of the K-T extinctions with others had disappeared millions of years earlier for any theory that proposes an abrupt and global eco- completely different reasons. Because the last of the logical catastrophe. dinosaurs disappear at the end of Cretaceous, we The Curtain Falls 231 often think of it as the dinosaur extinction when in Triceratops earlier in this chapter) and the dating of fact there was no such thing. Remember also that the deposits is only approximate. The basic problem we have no information at all on how the events here, once again, is the abundance and quality of the of the K-T transition affected creatures such as the data. We need many more fossils from additional insects, worms, and microbes that no doubt consti- localities preserved in well-dated sediments before tuted a major fraction of the Cretaceous biosphere a more certain perception of the timing and pace of just as they do now. It seems just a bit prema- the dinosaur extinction can be formulated. ture to refer to the K-T event as a “mass extinc- After several decades of vigorous and some- tion” when we are so uncertain about its effects on times acrimonious debate most scientists now agree the worldwide biota. This is not to deny that some- that very good evidence indicates that something thing unusual occurred at the end of the Cretaceous unusual occurred at the end of the Cretaceous. The but merely to suggest that our perception of it as a evidence for an exceptionally explosive event from major biotic crisis might reflect our preoccupation K-T sediments is compelling and includes not only with the dinosaurs and other large reptiles. iridium but also shattered (“shocked metamor- In addition to our uncertainty about the causes phosed”) quartz grains, tiny glassy spheres that and severity of the K-T extinctions, we are in equal probably represent droplets of liquified rock, and doubt about its pace. Was it a short event produced sootlike globules of carbon thought to be the fall- by a sudden catastrophe or a protracted decline out from global wildfires (Bohor and others 1984; resulting from the much slower progression of geo- Wolbach and others 1988; Belcher and others 2009). logical and biological processes? Data on the dis- Though few of these things have yet been found in tribution, abundance, and diversity of dinosaurs the North Horn Formation of Utah, they have been during the last few million years of the Maastrich- detected in enough of the world’s K-T deposits that tian age have been used to support both a sudden they can no longer be dismissed. These discoveries extinction scenario (Sheehan and others 1991; Fas- all indicate that something very explosive occurred tovsky and Sheehan 2005) and a slower-paced, more during the time when the last dinosaurs were strug- gradual decline (e.g., Carpenter and Breithaupt gling to survive. It is very likely that this event was 1986; Archibald 1996). In the Hell Creek Forma- the impact of an asteroid. Some scientists, however, tion of Montana, which produces almost all of our consider these features to be evidence of unusually information pertaining to dinosaur extinction, the violent and widespread volcanic activity. The recent number of genera of dinosaurs is nineteen at the discovery of a large impact structure of K-T age in base, twelve in the uppermost 60 feet, and seven at the Yucatan Peninsula of Mexico, along with depos- the very top (Lucas 1994). This general pattern sug- its of rubble around the Gulf of Mexico attributed gests a gradual decline rather than an abrupt disap- to the enormous waves generated by the impact, pearance of the last dinosaurs. On a global scale at has stimulated additional discussion of the proba- least fifty species of dinosaurs existed about 6 mil- bility of an asteroid impact. There is even some evi- lion years before the end of the Cretaceous, but dence for multiple impacts near the time of the K-T only around a dozen species are documented from extinctions (Keller and others 2002). strata deposited 2 million years prior to the K-T In addition to an asteroid impact, the late Cre- boundary layer, suggesting that an abrupt decline taceous world experienced several other global- in diversity began well before the end of the Creta- scale changes that could be related to the demise ceous. Such tabulations can be misleading, however, of the dinosaurs. As we learned in chapter 1, the because many of the species that are counted might end of the Cretaceous was a time of extraordinarily be invalid (recall my comments on the species of intense volcanic activity worldwide. Such a volcanic 8.13. Small mammals, such as these scavenging the remains of Alamosaurus, were among the survivors of the K-T extinctions. Illustration by Carel Brest van Kempen. The Curtain Falls 233 rampage could have modified the climate in ways reign. If so, then we can make no simple statements that might have resulted in biotic stress for the about the agent of dinosaur extinction. Many fac- dinosaurs and other victims of the K-T extinctions. tors were involved in a complex and interconnected Recall also that a rapid global regression of the sea way. With more and better data on the K-T bound- was underway at the end of the Cretaceous. The fall- ary events, we may someday be able to model these ing sea level would have altered the pattern of land interactions and demonstrate exactly how the K-T and ocean, inducing profound climatic changes in extinctions occurred. In the meantime be wary many locations around the world. The mixing of of short, sweet singular answers to the mystery of previously separated dinosaur faunas, as we have dinosaur extinction. At best they are oversimplifica- seen in the case of the appearance of Alamosaurus tions; at worst they are probably dead wrong. in North America, has been documented between Whatever ecological machinations may have other continents elsewhere in the world near the occurred during the K-T transition, the days of the end of Cretaceous time. When isolated popula- dinosaurs were over after the middle portion of the tions of animals are brought into contact with each North Horn Formation was deposited in Utah. In other, disease epidemics almost always follow as the subsequent epochs of the Tertiary period, espe- new pathogens are introduced into populations that cially the Paleocene and Eocene, the fossil record of have little resistance to them. Hence, in terms of the Utah is extraordinarily rich. Literally tens of thou- geological, biological, climatological, and even the sands of fossils have been collected from the early astronomical events of the time, the terminal Cre- Cenozoic strata in the High Plateaus, Uinta Basin, taceous was a chaotic episode in the history of our and other places in Utah. The study of these fos- planet. Any one of these phenomena might have sils reveals a magnificent menagerie of primitive caused the extinction of the dinosaurs, but it was mammals (fig. 8.13) but discloses no hint of the probably the biotic stress that resulted from their dinosaurs. The world had passed from the Age of combined effects that finally ended the dinosaurs’ Reptiles to the Age of Mammals. Chapter 9 Doing It 09The Allure of Paleontology Paleontologists have been studying dinosaur bones outdoor science. To do vertebrate paleontology you from Utah for nearly 150 years. During this time must have fossils. Fossils are not found in laborato- many thousands of fossil bones have been col- ries and libraries. Many paleontologists, of course, lected and analyzed by hundreds of scientists from employ high-tech approaches to the study of fos- all over the world. In the preceding chapters I have sils, such as the many computer-based techniques of summarized the results of this research and pre- imaging, analysis, and modeling. We have learned sented a general portrait of Utah dinosaurs and a great deal from the application of such technol- the world they inhabited, at least as they are cur- ogy, but the fossils themselves still represent the rently understood. After such a lengthy period of essential and fundamental data through which we study, and particularly in light of the recent frenzy gain insights on the vanished world of the dino- of field exploration and research, we might expect saurs. Recall from chapter 1 that the process of fos- that little remains to be discovered. It may appear silization produces numerous limitations in our to some readers that the glorious days of dinosaur basic data set. The fossil record is undeniably biased paleontology in Utah are artifacts of the past, like and fragmentary. Hence some of our questions may the dinosaurs themselves. But just the opposite is never be answered, at least to the degree of certainty true: however substantial our current knowledge of that we might like. Other questions, however, might Utah dinosaurs might seem, much more remains to be resolved by more and better data, when new fos- be discovered than has been learned thus far. Many sils are discovered that help us formulate a better questions still exist about nearly every dinosaur that idea of some aspect of the Mesozoic world. Find- has been documented in the Mesozoic fossil record ing these fossils is not always easy or simple, even of Utah. In spite of the many years of dedicated in a place like Utah where they are relatively abun- work by scientists, our knowledge of Utah dino- dant. The search for fossils can be a time-consuming saurs—their anatomy, their habits and habitats, and endeavor. This is one reason why the expansion of their evolution and history—is still severely lim- our knowledge of Utah dinosaurs has taken so long. ited. As is obvious from the earlier chapters of this How do paleontologists actually go about the book, we have many more questions about Utah business of finding dinosaur bones? While indi- dinosaurs than we do answers. Why have the results vidual paleontologists have their own unique strat- come so slowly? What might we anticipate in the egy for finding fossils, several steps in the process years ahead? How do people become involved in the are followed by most. The search for fossils is not quest to solve the many mysteries that remain about a random quest to find just any dinosaur remains. Utah dinosaurs? Instead specific fossils are targeted that will help Vertebrate paleontology is a unique science, answer a particular question. We might be inter- practiced by a rather peculiar breed of scientists. In ested in learning more about the species of a cer- the modern age of sophisticated analytical capabil- tain ceratopsian dinosaur (let’s say Torosaurus), ities vertebrate paleontology is still a field-based, for example. First, we have to become acquainted

234 Doing It 235 with everything that is currently known about this At this stage we are ready to embark on our expe- genus. This stage of our investigation might require dition. Many people envision that this expeditionary months of library research, compiling all the infor- phase of the work is all that vertebrate paleontology mation on Torosaurus that has been published. We is about, but it is just one step in a much longer pro- would also contact specialists in ceratopsian dino- cess, as we have seen. The general public often per- saurs to see if they have any additional informa- ceives field paleontology as an “Indiana Jones” sort tion that would help resolve our questions. Perhaps of adventure, but in reality it is most often much other scientists may want to join our effort and our less glamorous. It is still impossible to locate dino- project becomes a collaborative endeavor at this saur fossils from space, and no remote sensing tech- point. You may notice that single authors are rela- niques can reveal the presence of fossil bones over tively rare in the technical literature on dinosaurs a broad area, so actually finding our scientific trea- (much of which is cited in the bibliography of this sures requires walking . . . and walking . . . and walk- book). Collaboration in vertebrate paleontology is ing. This means dealing directly with all the hazards a time-honored tradition, because for most of our and discomforts of any outdoor activity: heat, thirst, questions two (or three or four) heads are better rugged terrain, rattlesnakes, insects, and weather, to than one. Eventually we may decide that our ques- name just a few. In addition, it is almost axiomatic tions cannot be addressed by existing fossils, so we that the best sites for the reconnaissance prove to begin to plan an expedition to find the material that be in very remote locations. In this case just getting might help provide answers. If our questions con- within walking distance of the outcrops can be a cern Torosaurus, we would not plan an expedition challenge that requires some rough (and often dan- to outcrops of the Morrison or Chinle Formations, gerous) four-wheel travel. Unexpected problems, both of which are older than any known ceratop- such as mechanical breakdowns or violent and nasty sian dinosaur. We would concentrate on deposits thunderstorms, pose obstacles to an expedition that of latest Cretaceous age (Maastrichtian), because are not quickly or easily overcome. Once in a while the ceratopsian dinosaurs were most abundant paleontologists get lucky and find significant fossils and diverse during that time. As discussed in the by stepping on them as they climb out of the truck. last chapter, we might have several different rock More commonly the fossils are located only after units and places to choose from in selecting the site days of laborious and exhausting reconnaissance. for our Torosaurus expedition. To make the best Once fossils are located, we make a preliminary choice, a paleontologist might spend days, weeks, assessment of their significance. The exposed por- or months compiling what is known about the tion of skeletal remains usually allows the paleon- stratigraphy, structure, and depositional environ- tologist to make a preliminary identification of the ments of Maastrichtian strata in Utah. We might bones, estimate the quality of preservation, and have to read scores of scientific papers, make doz- determine whether or not the material warrants ens of phone calls, and visit several different librar- additional effort. Sometimes we can’t be sure about ies. Ultimately we can select, usually from several these things on the basis of the scrappy and weath- possibilities, a field location where sediments that ered bone exposed on the surface, so some of the accumulated at the right time and under condi- concealing sediment is carefully removed from the tions favorable to the preservation of bones are fragile fossils. If it appears that the fossils might pro- well exposed. In this step of the process we have vide some useful information, it is time to begin improved our chances of finding fossils by targeting the excavation in earnest. The fossil bones normally an area where rocks of the appropriate age and ori- are not “dug up,” as is commonly thought. Instead gin are most accessible. the fossils are left in a block of rock matrix that is 236 Chapter 9

9.1. A plaster-jacketed block of fossils and rock matrix awaits transportation from the Hanksville-Burpee Dinosaur Quarry. Photo by Frank DeCourten. isolated from the barren sediment by carefully dig- in place, preventing damage or dislocation of the ging and chipping a slot around the fossil-bearing materials inside. The jackets traditionally are made rock. The isolation of the block may take days or by dipping burlap strips in plaster and wrapping weeks, depending on its size and delicacy: brushes, them around the block, on top of a layer of paper, dental tools, trowels, chisels, and ice picks are used plastic, or foil that serves as a separator (fig. 9.1). If to remove rock in small pieces. On rare occasions the block is large, strips of wood or lengths of steel the block and the fossils might be large and dura- rods (“rebar”) can be used to strengthen the cast. ble enough to allow power tools to be used at this Some paleontologists are beginning to use quick- stage, such as concrete saws and pneumatic drills. catalyzing resins and expanding foams in place of Penetrating hardeners (usually various adhesives plaster for jacketing the blocks. After the hard shell and glues thinned in a solvent) are applied to the is constructed and cured, the block is removed and delicate bones during the isolation process to pro- transported back to a laboratory for further work. tect them from the vibrations generated while the If a partial skeleton has been found, many blocks slots are cut. Once the fossil-bearing block is iso- may be required for its complete retrieval. In some lated, it is jacketed with a hard shell that will pro- very productive dinosaur quarries this effort may tect the fossils during removal and transport. The go on for many years before all of the fossils have idea here is similar to a physician placing a cast on a been collected. This is the case in several Utah sites, broken bone: the hard shell holds the rock and bone such as the Cleveland-Lloyd Quarry, the Dalton Doing It 237

9.2. The preparation lab in the former location of the Utah Museum of Natural History at the University of Utah. Photo by Frank DeCourten.

Well Quarry, and many others. The field excavation few weeks during the field season. Even more time phase may take a few days or may go on for decades. can be required if the fossils are particularly delicate But the work is far from over! or if full-time professional or volunteer prepara- The jacketed blocks are normally returned to tors are not available, as is the case in many muse- what is known as a “preparation laboratory,” which ums and colleges. The preparation of fossil bones may be anything from an enclosed loading dock or requires patience, skill, and tolerance for monoto- garage to a gleaming high-tech work room full of nous work. A good preparator can work wonders on specialized equipment (fig. 9.2). In the preparation fossil bones; an impatient or inexperienced one can lab the jackets are carefully opened and the metic- easily ruin a priceless treasure. ulous process of cleaning the rock matrix from the After preparation the cleaned fossils, which are fossil bones begins. This step in the process involves usually just bone fragments, are restored by assem- the use of tools ranging from tiny probes to minia- bling the pieces into complete bones and sealing ture sand-blasting machines to pneumatic chisels. the cracks with a fixative to avoid deterioration. In This work, the “preparation” of the fossils, is ago- general paleontologists try to avoid filling in miss- nizingly slow and requires considerable skill and ing portions of the bones, because this may alter patience. Haste in this delicate operation usually the original morphology in a way that might lead results in damaged or destroyed fossils. As a gen- to misinterpretation of its form. In most institu- eral rule paleontologists plan on at least a year of tions that house fossil collections the bones are work in the lab to prepare what was collected in a inventoried and assigned a number in a collections 238 Chapter 9 database. Important information accompanying dinosaurs today than at any time in history. Many the specimen, such as the geological horizon from of these scientists are engaged in studies designed to which it was collected, the precise geographic loca- address more than just the skeletal anatomy of dino- tion of the field site, the character of the enclos- saurs, which has been the traditional focus of our ing rock matrix, and other details are recorded in research for over a century. the data management system. The specimen then Second, advances in technology have resulted goes into storage until time is available for a detailed in many new tools of analysis, such as CT-scan- study of it or a replica is made from it or it goes on ning devices and DNA sequencing techniques, that display in a museum exhibit. were unheard of just a few decades ago. In addition, This entire process in vertebrate paleontology, the cladistic method of working out dinosaur fam- from the outset of the library research to the cat- ily trees has changed some of our older perceptions aloging of the prepared fossils, may take decades. of dinosaur relationships that were based on the This is why so many dinosaur projects are in a per- traditional morphometric approach. In combina- petual “ongoing” state. For example, recall that tion, these factors are allowing scientists to confront bones were first discovered at Dinosaur National such interesting aspects of the dinosaurs as their Monument in 1909 and at the Cleveland-Lloyd behavior, their patterns of dispersal, their evolu- Quarry in the 1930s. Both of these sites are still pro- tionary histories, and their physiology in ways that ducing new information and probably will con- were unimaginable in the early twentieth century. tinue to do so indefinitely. More recent discoveries The future of dinosaur paleontology is promising, in Utah, such as the Gaston Quarry, the Hanks- and we can look forward to many exciting discov- ville-Burpee Quarry, or the many new localities in eries. The nature of the dinosaur fossil record may the Grand Staircase–Escalante National Monument, not allow the complete resolution of all the pres- are not likely to be exhausted during the lifetime of ent mysteries about dinosaurs, but the present flurry anyone reading this book. The point is that we can’t of interest will almost certainly settle some of the expect quick answers to the many questions about debates. What is particularly appealing about the Utah dinosaurs that can only be resolved by more current frenzy of interest in dinosaurs is that almost and better fossils than are currently available. Even- anyone can play a role in it. tually we will know more about the Mesozoic world Vertebrate paleontology has traditionally been and its inhabitants, but we must be patient. That is more accessible to a wider range of practitioners the nature of vertebrate paleontology. than most sciences have been. Many important dis- Over the past several decades the study of dino- coveries have been made by amateurs with little or saurs has experienced a renaissance of sorts. While no academic background in the subject but with a the fossils will always be the essential data on these compelling interest in the life of the past. It doesn’t fascinating creatures, we are beginning to move take much more than persistence and passion to beyond the simple description of new types and find dinosaur bones and to make important contri- into fields of research that may open completely butions to paleontological knowledge. Imagine try- new vistas on the Mesozoic world. This expan- ing to discover a new subatomic particle in your sion of knowledge and perspectives is attributable garage, unraveling the structure of DNA in your to several factors. First, over the past twenty years kitchen, or studying the surface of Neptune’s moons or so the number of scientists studying dinosaurs from your back porch. Success in such scientific and dinosaur-related issues, such as the K-T extinc- efforts would be unlikely. But in vertebrate paleon- tions and Mesozoic paleobiogeography, has dramat- tology, where all knowledge is derived from fossils, ically increased. More paleontologists are studying a good pair of hiking boots and the information on Doing It 239 what to look for and where to find it are all that is In any event no one should hesitate to contact pale- required for a breakthrough discovery to be made. ontologists in a local museum or college about vol- As described above, however, developing the full unteer opportunities in paleontology. You’ll almost potential of a new discovery is not easy or simple. always be welcomed aboard. For this reason it is important that people interested Many areas have organizations that can help in becoming involved in the effort to expand our make connections between “professional” paleon- understanding of dinosaurs do so in collaboration tologists and amateurs. The Utah Friends of Pale- with scientists in universities and museums. This ontology, a statewide association with numerous is not because vertebrate paleontology is the sole local chapters, has been heavily involved with pale- domain of the “privileged” academics and/or their ontological excavations and community education “elite” institutions. Paleontology is a science for all for many years. The local chapters of such organiza- people. But scientists with experience in field pale- tions are commonly based at community museums ontology and with access to properly equipped lab- or colleges. A simple inquiry about organizations oratories can spare the amateur collectors the cost of this type will usually get you started on the right and trouble of acquiring those things on their own. track. If your area has no museums or colleges, try They can help the amateurs target the search for calling the nearest one. One or more of your neigh- new fossils and can assist in properly completing bors might already be involved in paleontology and the various stages of work that will be required for can perhaps give you guidance in getting involved. any discovery to have full impact. In most museum The Utah Geological Survey sponsors a Paleon- and university programs in vertebrate paleontology tology Volunteer Certificate Program that is an the involvement of volunteers is not only welcomed excellent first step in making connections with pro- but desperately needed. This is because there are fessional scientists. For institutions and agencies actually very few professional paleontologists. My in Utah that have active programs in paleontology, guess is that probably fewer than 150 people were see the list at the end of this chapter. In other areas hired as paleontologists in the United States. Most check with your local equivalents to these orga- of us work as college professors, as museum profes- nizations. Land management agencies such as the sionals, or in government agencies. This, of course, National Park Service, Utah Division of State Lands, means that we have other tasks that seem to take and Bureau of Land Management can also help up nearly all of our available time. Hence we would people get involved with paleontological programs accomplish little if not for the volunteers willing to operating on the lands that they oversee. lend assistance in the lab and in the field. Because In addition to maximizing the value of your so few scientists are actually employed specifically efforts, there is another reason for channeling your as paleontologists, I suppose that it is not inaccurate interest in paleontology through a volunteer orga- to view most of us as amateurs. We are, as a gen- nization or individual contact with an institution. eral rule, motivated by the same things that stir the As a consequence of the passage of the Paleonto- amateur collector to action: the sheer excitement of logical Resources Preservation Act of 2009 (PRPA), exploring an ancient world and the thrill of discov- part of the 2009 U.S. Omnibus Public Land Act, ering the unknown. Perhaps that is one reason why the removal of vertebrate fossils from federal public such a strong professional-amateur bond has existed lands is illegal without permits from the appropri- throughout the history of vertebrate paleontology. ate agency. Similar standards and procedures have We are all united by something much more power- been adopted by the State of Utah and are managed ful than the superficial distinctions that separate us, under the office of the Utah state paleontologist. such as academic degrees and professional stature. Utah is a state consisting predominantly of public 240 Chapter 9 land, an expansive mosaic of parcels managed by world and with diverse talents. Maybe this results the U.S. Forest Service, U.S. Bureau of Land Man- from the necessity of applying concepts from a vari- agement, National Park Service, U.S. Department ety of scientific disciplines in paleontology. After all, of Defense, the State of Utah, and many counties to understand the events documented in the fos- and municipalities. In addition, substantial tracts sil record we need to master the fundamental ideas of land in Utah are under the jurisdiction of vari- of biology, geology, chemistry, physics, and other ous tribal agencies within Native American reserva- sciences. My personal suspicion is that the unique tions, and most of these also regulate the collection nature of paleontological inquiry requires even of fossils and other antiquities. Regardless of the more versatility. Many times it is as important for management agency involved, permits for collecting paleontologists to be able to repair a broken fuel vertebrate fossils are rarely issued to private individ- pump as it is to construct a cladogram. Most pale- uals. This is due to growing concern over the looting ontologists can do both. Paleontologists need to and vandalism of dinosaur fossil sites by unau- develop skill in using dental tools on very delicate thorized private collectors. Since the passage of the specimens but also have to confront moving blocks PRPA laws protecting paleontological resources on of rock that weigh several hundred pounds. This public lands are now as stringent and clearly defined multidimensional yin-and-yang of vertebrate pale- as those protecting archaeological resources under ontology breeds a unique genre of scientists, people the Archeological Resources Protection Act of 1979. fascinated by the innumerable intricacies of the nat- The impetus for the PRPA of 2009 was in large part ural world and possessing an uncommonly broad the concern over the loss of valuable scientific infor- array of talents. In general vertebrate paleontolo- mation as unscrupulous private collectors vandal- gists are fun to be around. Most tend to be generous ized many significant vertebrate fossil localities for with their knowledge, unassuming, and thrilled to personal gain via the international black market share their zeal for prehistoric life with anyone. In a in dinosaur fossils. Sadly, any paleontologist who crowd of dinosaur paleontologists you will probably spends much time in the field can relate stories of encounter more colorful characters, more diverse specimens lost or destroyed by vandals. So protect- viewpoints, and a wider range of personalities than ing paleontological resources on public land makes is typical of society at large. You’ll also develop a good sense and helps preserve public property for whole new dimension in your sense of humor if you the benefit of all through scientific research and new hang around long enough. Seen against the back- insights. Accordingly it is usually very difficult for drop of millions of years of evolution and extinc- private individuals unaffiliated with a paleontolog- tion, the conventions and customs of modern ical organization or academic institution to secure human society take on an almost comical guise. a collecting permit for vertebrate fossils. Involve- Vertebrate paleontologists, by virtue of their unique ment with a museum, college, or recognized organi- perspective on the history of life and human exis- zation obviates the problem of a permit and ensures tence, tend to see our world a bit differently from that the best uses will be made of whatever new fos- most folks. You will enjoy their company. sil material you locate. Another benefit of channeling your inter- S o You Want to Be a Paleontologist? est in dinosaurs through an institution or organization (perhaps the most attractive advantage of Sooner or later all paleontologists are asked how to all) is the people you will meet. Vertebrate paleon- prepare for a career as a dinosaur paleontologist. It is tology for some reason has traditionally attracted usually but not always younger people who ask this people with a wide range of interests in the natural question. Fearful of quenching youthful enthusiasm, Doing It 241

I normally respond with a reminder that paleon- at a snail’s pace. It might eventually stop dead in its tology is a unique discipline that requires academic tracks, if the winds of academic fashion continue preparation in the basic sciences and mathemat- to blow against us. There are simply too few profes- ics. Careers in paleontology are best built upon such sionals to address the many questions and mysteries a foundation of knowledge. But it might be bet- concerning the dinosaurs—and always will be. So ter advice simply to say, “Don’t bother!” Remember the best way to join the excitement of exploring the that there are very few professional paleontologists prehistoric world is to get involved with the institu- and that opportunities for gainful employment in tions and organizations that are struggling to keep the field are severely restricted. This bleak employ- paleontology alive. They need your help and, in ment outlook, despite the public frenzy over dino- turn, can provide an avenue for the fulfillment that saurs, seems to be getting worse not better. Many comes from active participation in scientific work. museums that proudly display dinosaur skeletons in To contribute to paleontology you don’t necessar- their exhibits don’t have vertebrate paleontologists ily need to be a “professional,” especially if you wind on the staff. Several research-grade fossil collections up as an unemployed professional, as is likely these have been transferred from prestigious universi- days. All you really need is the passion for learning ties during the past decade, as more and more insti- about the history of life on our planet and the ini- tutions eliminate or deemphasize paleontology as a tiative to make contact with people sharing that fer- part of the science curriculum. Fortunately several vor. Anyone reading this book can make valuable public institutions in Utah have reversed this general contributions to this never-ending quest to resolve trend in recent years by expanding their paleontol- the mysteries of the past. By your interest in Utah ogy programs. Still, funding for paleontological proj- dinosaurs you have already demonstrated the pri- ects is becoming increasingly difficult to acquire in mary qualification for involvement in paleontology: comparison with funding for other scientific fields. the enthusiasm for learning about prehistoric life. This trend has been the subject of extensive discus- And that is all it really takes. An amazing world of sions among paleontologists. The reasons for it are discovery awaits you in the wild splendor of Utah’s numerous and complicated, but in reality profes- dinosaur country. sional opportunities in paleontology are not likely to expand anytime soon. So should young (or older) Institutions and Organizations in Utah people be discouraged from pursuing an interest that with Active Programs in Paleontology will not likely result in any viable career options for them? Absolutely not! Even if the chances of estab- Brigham Young University lishing a career in paleontology are very remote, a Museum of Paleontology lifetime of wonder and awe is a more than adequate 1683 N. Canyon Road reward for all who seek to comprehend the life of the Provo, Utah 84602-3300 past. Whether or not we get paid to participate in 801-422-3680 this intellectual journey is not nearly as important as http://cpms.byu.edu/ESM simply doing it. It is precisely the deficiency of opportunities in Natural History Museum of Utah the paleontology job market that makes the involve- University of Utah ment of “nonprofessionals” so critical. Without the 301 Wakara Way interest and commitment of the general public, the Salt Lake City, UT 84108 growth of knowledge about dinosaurs or any other 801-581-4303 group of prehistoric creatures would crawl along http://nhmu.utah.edu 242 Chapter 9

Museum of Natural Science/Department of Geology Utah State University-Eastern Prehistoric Museum Weber State University 451 East 400 North 1551 Edvalson Street Price, Utah 84501 Ogden, UT 84408 435-613-5060 801-626-6160 http://www.ceu.edu/museum http://webersci.org Office of the Utah State Paleontologist Dinosaur National Monument Utah Geological Survey P.O. Box 128 1594 W. North Temple Jensen, UT 84035 P.O. Box 146100 435-781-7700 Salt Lake City, UT 84114-6100 http://www.nps.gov/dino 801-537-3307 http://www.blm.gov/ut/st/en/prog/more/cultural/ Cleveland-Lloyd Dinosaur Quarry Paleontology.html River Field Office Bureau of Land Management Utah Friends of Paleontology 125 South 600 West c/o Martha Hayden Price, UT 84501 Utah Geological Survey 435-636-3600 P.O. Box 146100 http://www.blm.gov/ut/st/en/fo/price/recreation/ Salt Lake City, UT 84114-6100 quarry.html http://utahpaleo.org/

St. George Dinosaur Discovery Site at Johnson Farm Grand Staircase–Escalante National Monument 2180 East Riverside Drive 190 E. Center Street St. George, Utah 84790 Kanab, UT 84741 435-574-3466 435-644-4300 http://www.dinosite.org http://www.utah.com/nationalsites/ grand_staircase.htm Utah Field House of Natural History 496 East Main Street Vernal, UT 84078-2605 435-789-3799 http://www.utah.com/stateparks/field_house.htm Appendix: Classification of Dinosaurs

Dinosaurs are unquestionably the most familiar of To Owen, the fossils were clearly of reptilian charac- all prehistoric creatures. For nearly a century repre- ter, though at the time there was some controversy sentations of these animals have been a notable ele- concerning the type of animals that they repre- ment in our popular culture, appearing in movies, sented. Owen invented his new term from Greek books, and posters, as toys, on children’s lunch pails, roots that mean literally “terrible lizards” or “terrible and in myriad other forms. Consequently most of reptiles.” Why did he consider these reptiles “terri- us became aware of the general appearance of dino- ble”? It was probably because they were unbeliev- saurs at an early age and soon learned to pronounce ably large in comparison to today’s reptiles. Owen their names and identify a few of the basic types. A must have developed a fearsome perception of what likeness of a Tyrannosaurus is for most of us as iden- these animals would have been like while alive. tifiable as a photograph of the family dog. Few of Since Owen’s time thousands of dinosaur fos- us would have difficulty recognizing a dinosaur if it sils have been collected from localities all over the were to walk down the street in front of our house. world, including the most remote places such as If we were asked to give a precise definition of Antarctica. Every time a new “terrible lizard” was the group of reptiles known as dinosaurs, however, discovered, it was placed into Owen’s group if it was we might find ourselves hesitating a bit. We might large, reptilian, and extinct. It wasn’t long before immediately respond that dinosaurs were large rep- paleontologists began to wonder about the basic tiles that lived long ago and are now extinct. That biological characteristics of all the varied types of definition might suffice for a few of the best-known dinosaurs that were being discovered and sought and most popular types of dinosaurs such as Tyran- to define the term more precisely. In addition, by nosaurus, Stegosaurus, Apatosaurus, and Triceratops. the late 1800s it was becoming increasingly obvi- But glance through any book on dinosaurs and you ous that, with so many different types of dinosaurs, will soon discover that these reptiles were amaz- a classification scheme should be developed that ingly varied in terms of size, shape, behavior, anat- would allow us to place similar animals together in omy, and general appearance. The dinosaurs are so smaller groups of closely related types. Paleontolo- diverse that paleontologists have named as many as gists had considerable differences of opinion on the 800 different types (though not all of these are cur- definition of the dinosaurs and their classification. rently considered valid—more on this later). When Even today they continue to disagree on precisely we ponder the incredible variety of dinosaurs, we how to subdivide these reptiles into smaller groups might wonder what set of characteristics they all of similar and related animals. shared. What is it about dinosaurs that allows us to Thus there is still some ambiguity about classi- recognize them so easily and place them together in fying dinosaurs into taxonomic categories such as a group that is distinct from other reptiles? species, genera, and families. These uncertainties are The term “dinosaur” was first used in 1842 by compounded by the fact that many dinosaur spe- Richard Owen, the illustrious British anatomist, to cies have been identified on the basis of very frag- embrace a small number of large prehistoric reptiles mentary fossils (Carpenter and Currie 1990). The that were then known only from a handful of fossils. following discussion presents what I believe is the

243 244 Appendix consensus view among modern dinosaur paleon- of reptiles contains dinosaurs. Likewise, dinosaurs tologists. Understand that our modern definition did not fly or glide through the air. The Mesozoic of the dinosaurs and the system we use to clas- skies were full of aerial reptiles (known as ptero- sify them have both been evolving since Owen saurs), but none of them are true dinosaurs. Some first coined the term. In the future, as more fos- dinosaurs may have been able to climb trees or per- sils are discovered and our knowledge of dinosaurs haps dig shallow burrows in the ground, but such becomes more complete, we will probably modify habits were merely variations on the general theme the current classification to accommodate both the of terrestrial adaptations. new discoveries and our changing perceptions of Reflecting their adaptations to terrestrial envi- the relationships among various groups. Such is the ronments, the skeletons of all dinosaurs exhibit nature of any classification scheme; they are never some common architectural patterns (fig. A.1). All static, because human knowledge of any aspect of dinosaurs possessed at least three vertebrae in the nature is always expanding. sacrum, that portion of the backbone that was connected to the bladelike hip bone (ilium). Some dinosaurs had as many as six or seven vertebrae in Dinosaurs Defined the sacral portion of the backbone, fused into a solid Modern paleontologists are in general agreement mass of bone. This relatively rigid bracing allowed that all dinosaurs, regardless of their individual spe- dinosaurs to transmit the thrust of the hind legs to cializations and characteristics, possess an array of the body effectively. In addition, the dinosaurs had characteristics that collectively sets them apart from an erect posture with the limbs positioned vertically other groups of reptiles. Dinosaurs had at least a beneath the body. This stance allowed them to move dozen (more, according to some paleontologists) over land much more efficiently than other reptiles unique skeletal characteristics that can be used for (e.g., the crocodiles and lizards), which have a more formal definition of this group of reptiles (Novas sprawling pose with the limbs extended outward 1996; Nesbitt 2011). It is important to remember that from the body. The erect positioning of the limbs of no single characteristic defines an animal as a dino- dinosaurs is reflected in the shape and configuration saur. Instead it is the combination of many traits of the femur (thigh bone), acetabulum (opening in that characterize the group as a natural subdivi- the hip socket), ankles, and feet. The femur is the sion of the reptiles. While it is beyond our scope largest bone in the hind limb and in dinosaurs typi- to list all the detailed skeletal features that distin- cally has an offset head connected to the main shaft guish the dinosaurs as a group, we should at least by a narrowed neck of bone (Fig. A.1A). The angled become familiar with a few of their most important head of the femur inserted into a hip socket that was attributes. at least partly open, and the upper hip bone (ilium) First, all dinosaurs were inhabitants of the land, had a strong bony crest that buttressed the offset with specializations that enabled them to move effi- end of the femur (Fig. A1.B). The main shaft of the ciently across the dry terrain. Many dinosaurs were femur could thus be positioned vertically under the well adapted to live in coastal plains, along river dinosaur while the head of the femur was inserted courses, or in swampy regions, where the land and into the pelvis at an angle. The open arrangement of water met. But none of the animals that we call bones around the hip socket allowed a deeper inser- dinosaurs were specifically adapted to live exclu- tion of the femur and a more rigid bracing of that sively in the water. The long-necked plesiosaurs and bone to the pelvis. the dolphinlike ichthyosaurs were well adapted for The structure of dinosaur ankles and feet reveals life in the Mesozoic seas, but neither of these groups additional specializations for terrestrial locomotion. Classification of Dinosaurs 245

A.2. The mesotarsal ankle of dinosaurs (right) compared to the crurotarsal ankle of crocodiles (left). The relatively simple hingelike motion of the dinosaur ankle allowed greater efficiency and stability in terrestrial locomotion. The heavy black line indicates the axis of flexure in the ankle. A = astragalus bone; C = calcaneum.

stood only on their toes (digitigrade condition), A.1. Some unique skeletal features of dinosaurs: A. femur with offset head joined to main shaft via a nar- with the ankle elevated high above the ground by rowed neck; B. pelvis with an opening (the acetabulum) the elongated foot bones known as metatarsals in where the end of the femur inserts; C. simple hingelike the hind foot or metacarpals in the fore foot. Of mesotarsal ankle; note that this example has only three the five toes in a typical reptile foot, one or two are well-developed toes, rather than the five seen in most modern reptiles; D. dinosaur hand with a somewhat either strongly reduced or absent in the feet of dino- opposable first digit or “thumb”; E. typical dinosaur saurs. The effect of this foot and leg structure was skull (Ceratosaurus). On either side of the skull behind to increase the overall length of the leg, extend the the orbit (eye socket) are two openings: the lower tem- stride, and minimize the frictional contact with the poral fenestra and the upper supratemporal fenestra. The presence of these two openings identifies dinosaurs ground. These are all specializations for efficient as members of the subclass Diapsoda. running and walking on land. The modern horse has evolved some of these same basic adaptations, The ankles of dinosaurs were uniquely designed to superimposed on a mammalian rather than reptil- allow great flexibility in the fore-aft direction and a ian body plan. minimum of inward-outward movement (fig. A.1C). The hands of dinosaurs were also modified in The simple hingelike arrangement of bones in the ways that are unique among reptiles. The outermost dinosaur ankle is known as the mesotarsal condi- two fingers (digits IV and V; the “pinky” and the tion and allowed the dinosaurs to propel them- “ring finger”) were strongly reduced or missing alto- selves forward with speed, efficiency, and stability. gether. In addition, digit I (the “thumb”) was usu- This mesotarsal ankle is a key feature that unites the ally twisted somewhat so that it was at least partially dinosaurs with the birds and pterosaurs within the opposable to the other two fingers (fig. A.1D). This clade Avemetatarsalia. The Crurotarsalia, another specialization permitted bipedal dinosaurs to use major group of reptiles, have a more flexible ankle their hands for grasping and manipulating objects construction, which, among other things, sepa- in ways that modern reptiles cannot. In many qua- rates the crocodiles and lizards from the dinosaur- drupedal dinosaurs the hands were modified much bird lineage (fig. A.2). In addition, most dinosaurs like the feet to provide support and efficiency of 246 Appendix

Classification of Dinosaurs movement: the bones of the hand were relatively robust, and the tips of the “fingers” bore small hoof- All fossils are assigned to various groups under the like structures known as unguals. The “hands” of same system of classification used by biologists for quadrupedal dinosaurs looked more like “feet” living creatures. This system has seven main hier- because they were modified to support the body archical levels of classification as follows, using rather than to manipulate objects. humans as an example: The skulls of dinosaurs were constructed from dozens of bones and were highly varied Kingdom: Animalia (all animals) in response to the specializations of diet, sen- Phylum: Chordata (all chordates) sory organs, behavior, and other factors. But even Class: Mammalia (all mammals) a brief examination of the skull of any dinosaur Order: Primates (humans, apes, lemurs, reveals that it had more openings and cavities monkeys) among the various bones than are present in most Family: Hominidae (humanlike primates) modern reptiles. The specific pattern of the open- Genus: Homo (modern or nearly ings is different in the various types of dinosaurs, modern humans) but they all had two perforations on either side Species: sapiens of the skull behind the orbit (eye socket). These two openings are known as the temporal fenes- Even though it is sometimes difficult to apply this trae and the paired holes identify the dinosaurs system of classification to ancient life, it does allow as diapsid reptiles (fig. A.1E). Among the modern us to arrange organisms in groups of more or less reptiles, only crocodiles and the primitive sphen- related and similar types. Note that as we proceed odontid lizards retain the two complete temporal from the highest level (kingdom) to the lowest level fenestrae. Turtles have no temporal openings at all; of classification (species) the categories become snakes and lizards have a modified diapsid pattern increasingly exclusive and contain both fewer and of temporal openings. The other perforations in more similar groups of organisms. The kingdom the skulls of dinosaurs are related to the distribu- Animalia encompasses all kinds of animals, while tion of stresses in the skull, the attachments of cer- the species sapiens contains just one type. In addi- tain muscles in the head and jaws, or the housing tion to these seven main levels of classification, sci- of special organs and glands. Most dinosaurs had entists sometimes recognize intermediate levels. a very flexible skull with movable joints between For example, a suborder is a level of classification many of the individual skull bones. In contrast, the below the order but above the family. Thus a subor- skulls of most mammals (yours, for example) are der is a group of organisms more restrictive than an formed of only a few rigidly fused, platelike bones order but more inclusive than a family. A superfam- that have little flexibility. The dinosaur brain was ily, similarly, is a group of several families but more housed inside a bony capsule (brain case) that was restrictive and less inclusive than an order. Some- located within the perforated shell formed by the times a subcategory can be further divided into bones of the skull. In short, the skulls of dinosaurs even smaller assemblages. An infraorder, for exam- were more open and more loosely assembled than ple, is a subset of a suborder but is still a larger array are the skulls of most mammals. This is one rea- of organisms than a family or a superfamily. son why it is so rare to find a completely preserved We will begin our review of dinosaur classifi- dinosaur skull with all the bones connected and cation at the class level: as we have seen, all dino- intact. saurs are members of the class Reptilia. This class, of Classification of Dinosaurs 247 course, includes all other reptiles living and extinct, they consist of two separate orders and include ani- of which there are hundreds. The classification of mals that were not necessarily closely related. To use reptiles, even if we consider only the living types, is a more familiar illustration, recall that the mam- not really very straightforward. This is because the mals are a class (Mammalia), just as are the reptiles. reptiles are extremely varied and as a class include There are about two dozen different orders of living many different types. Things become even more and extinct mammals. We belong to the order Pri- confusing if we include the extinct reptiles in our mates. Elephants belong to the order Proboscidea. classification as well. Many of the ancient forms, like People and elephants are much different creatures, the dinosaurs, are not comparable to any modern and no one would consider us closely related to ele- group and thus can’t easily be placed in any cate- phants. Yet we are as similar to elephants as the vari- gory of living reptiles. The reptiles have traditionally ous ornithischian and saurischian dinosaurs were to been subdivided into subclasses based on the pat- each other. tern of openings in the skulls (temporal fenestrae). The two orders of dinosaurs are established on the Dinosaurs belong to the subclass Diapsida because, basis of the arrangement of bones in the pelvis. The as we have seen, they all had two temporal openings reptilian pelvis has three large bones: the bladelike in the skull. Diapsida, however, includes more than ilium, the down-and-backward projecting ischium, just dinosaurs. We also place the sphenodontid rep- and the pubis, positioned in front of the ischium and tiles, crocodiles, snakes, and lizards into this group, below the ilium (fig. A.3). In one order of dinosaurs, even though the latter two groups have a modified the Saurischia, these three bones diverge from each diapsid pattern of temporal openings. Consequently other in a triradiate form, with the pubis extend- Diapsida is still a large subgroup of reptiles that begs ing down and forward from the center of the pelvis. for subdivision. Because snakes and lizards have In the Ornithischia the pubis is positioned more or both modified the original diapsid pattern by reduc- less parallel to the ischium and thus projects back- ing the lower fenestra to only a partial opening they ward and down from the hip socket. In many ornith- are placed together in the infraclass Lepidosauria. ischian dinosaurs the pubis has a forward projecting The lepidosaurs are thus the “modified diapsids”; all prong that protrudes beneath the anterior (front) other diapsid reptiles retain two complete tempo- portion of the ilium. These two orders of dinosaurs ral fenestrae. These nonsnake and nonlizard diapsid were named and defined in 1888 by H. G. Seeley reptiles all belong to the infraclass Archosauria. because the construction of the pelvis of dinosaurs is The Archosauria include dinosaurs, crocodiles, similar to that of either modern lizards (saurischians) extinct pterosaurs, and living sphenodontids along or living birds (ornithischians). We suspect now, of with many other less familiar extinct groups. These course, that some dinosaurs are very closely related subgroups of archosaurs are usually separated into to birds; in fact the ancestors of the birds probably formal orders: the crocodiles into the order Croco- were early dinosaurs. Confusingly, though, these bird dilia, the pterosaurs into the order Pterosauria, and ancestors were members of the order Saurischia, not so on. The dinosaurs, however, have been placed the Ornithischia as we might expect from the names into one of two orders: the Ornithischia and the alone. It appears that the avian style of pelvic design Saurischia. This is an important and unique point evolved at least twice: once in the ornithischian dino- in the classification of the animals we call dinosaurs and again among the true birds as they devel- saurs: this group actually consists of two orders of oped from their saurischian dinosaur ancestors. We organisms. Whenever we contemplate the relation- will examine the dinosaur-bird connection in a little ships among dinosaurs, we should remember that more detail later in this appendix. 248 Appendix

Saurischian Dinosaurs

Two suborders have been established among the Saurischia: the Theropoda and the Sauropodomor- pha. The Theropoda (theropods) were all bipedal carnivores such as Tyrannosaurus and Allosau- rus, the state fossil of Utah. But not all theropods were as large and fearsome as these giants. The 20-pound Compsognathus, one of the smallest dinosaurs known, also belongs to this group. On the basis of the details of the skull, teeth, vertebral column, limbs, and feet the theropods have been subdivided in two groups: the Ceratosauria and the Tetanurae. The Ceratosauria include the earliest and most primitive of the theropods and are typified by dinosaurs such as Dilophosaurus, Coelophysis (one of the earliest dinosaurs from North America), and of course Utah’s own Ceratosaurus, the namesake for the group. The Tetanurae are more highly specialized theropods and include a great variety of bipedal carnivores. Several families have been established among the tetanurine theropods, including A.3. Pelvic structure of dinosaurs: A. pelvis of Cerato- saurus, a saurischian dinosaur; B. pelvis of Scelidosau- the Allosauridae (Allosaurus and close relatives), rus, an ornithischian dinosaur. Note that in the older the Tyrannosauridae (including Tyrannosaurus and Saurischia (A) the pubis extends forward and down Albertosaurus), the Dromaeosauridae (small and from the center of the pelvis to form a triradiate pattern. In the Ornithischia (B) the pubis is positioned more par- swift predators with large slicing claws on the hind allel to the ischium, which projects down and back from feet), the Ornithomimidae (medium-sized, mostly the center of the pelvis. toothless birdlike carnivores), and several others less common in Utah. Both the Saurischia and the Ornithischia are The Sauropodomorpha (sauropods) were large diverse orders. Each of these two great dinosaur quadrupedal, herbivorous saurischians. Perhaps the groups consists of scores of different types. So var- most familiar of the great sauropods is Apatosaurus, ied are the orders that paleontologists have subdi- commonly (though inaccurately) known as Bron- vided each into a number of suborders that, in turn, tosaurus. Weighing in at over 50 tons for the big- have been divided into infraorders, superfamilies, gest types, the sauropods included the largest land and families. At these lower levels of classification, animals to ever live on the earth. Most of the sau- there is still no universal agreement on how best ropods had very small heads supported on long to define the various subgroupings and which cat- necks, a massive body, and a long tail. To support egories have which taxonomic rank. The following their immense mass, the limbs of sauropod dino- summary represents a consensus view among most saurs were designed to function like massive col- paleontologists and emphasizes those groups of umns positioned vertically beneath the body. The dinosaurs that are important in Utah. Other classi- bones of the feet were thick and robust, splayed out fication schemes have been proposed and might be to support a nearly circular pad of shock-absorb- favored by some scientists. ing cartilage, much like the foot of an elephant. Classification of Dinosaurs 249

Paleontologists have long marveled over the small sauropods, with extremely long necks and tails. The heads and relatively simple dentition of the sau- neck of the largest individuals of Diplodocus, for ropods, which seem to be inadequate for process- example, was nearly 35 feet (about 11 meters) long ing the large amounts of plant food that they would and was constructed from fifteen individual ver- have required, with so much mass to sustain. The tebrae. The tails of the diplodocids were extremely sauropods probably had accessory masticating long, consisting of as many as eighty vertebrae, and organs or elaborate digestive pathways that enabled gradually tapered to a slender, whiplike tip. The them to consume and process great amounts of diplodocids were the longest of all the great sauro- plant fodder. pods but not the heaviest because of their slender The suborder Sauropodomorpha is subdivided physique. The many different kinds of diplodo- into at least five families. Among Utah’s sauropods, cid sauropods include (in addition to Diplodo- the three most important families are the Brachio- cus) Apatosaurus, Barosaurus, Mammenchisaurus sauridae (brachiosaurids), the Camarasauridae (from China), Seismosaurus, and Dystylosaurus. The (camarasaurids), and the Diplodocidae (diplodo- Titanosauridae, represented in Utah by Alamosau- cids). A fourth group, the Titanosauridae, is also rus of late Cretaceous age, is a poorly known family present in the late Cretaceous, but this family is consisting of only three genera that are reasonably much less common in Utah than are the other three. well represented in the fossil record. The titanosau- The brachiosaurids are typified by Brachiosaurus, rids were medium to large-sized sauropods, rang- the namesake for the group, which had longer fore- ing in length from about 35 to 65 feet (about 12 to 22 limbs than hind limbs. The humerus (upper fore- meters). One of the most distinctive aspects of the limb bone) was as long as or sometimes longer than titansaurids is the body armor, consisting of small the femur (thigh bone) in brachiosaurids, raising circular nodes of bone in the skin. The armored skin the shoulders above the hips. This unique charac- is only known in Saltosaurus, but it may have been teristic gave the brachiosaurids a giraffelike pos- present in other genera of this family. The titano- ture. The tails of brachiosaurids were relatively short saurids also had very distinctive tail vertebrae, fea- and thick compared to those of other groups of sau- turing a hollow cavity on the front end and a convex ropods. The brachiosaurids were the largest of all “ball” on the rear surface. dinosaurs, including the enormous Ultrasaurus. The earliest dinosaurs known from the fos- The camarasaurids were modest-sized sauropods, sil record were saurischians. They were relatively with overall body length ranging from 40 to 60 feet small but otherwise similar to the theropods in that (13–20 meters). The most distinctive characteris- they had a bipedal stance and carnivorous habits. tic of the camarasaurids was the blunt, bulldoglike As the theropods evolved steadily throughout the snout, with the nostrils placed high on the fore- Mesozoic, the ceratosaurs and various tetanurines head above the eyes. The teeth of the camarasaurids emerged through the development of numerous were thick, broad, and gently curved into a spoon- specializations that were superimposed on the gen- like shape. They had relatively short and muscular eralized architecture of their ancestors. The sauro- necks compared to other sauropod dinosaurs. The pods represent a radical departure from this basic forelimbs of the camarasaurids were slightly shorter design. The herbivorous diet and quadrupedal pos- than the hind limbs. The diplodocid sauropods had ture of the sauropods occurred in response to their distinctive long and slender skulls, with simple peg- exploitation of a new ecological opportunity as a like teeth. The nostrils of diplodocids were posi- large terrestrial browser. Taking advantage of the tioned on top of the head, just a little in front of the abundant plant food available in the lush Mesozoic eyes. The diplodocids were lightly built and slender forests required some revolutionary changes in the 250 Appendix basic saurischian anatomy. A larger and more com- hind foot would have “reemerged” in the sauropods plex digestive system was required to process plant after it was reduced in their ancestors. Thus the pro- fodder, which contains durable organic compounds sauropods are probably not the progenitors of the such as cellulose and lignin. These compounds are later sauropods. Instead these two groups are more so tough as to be nearly indigestible. In comparison likely descended from a common, albeit unknown, to meat and other animal tissues, vegetation is also a theropodlike ancestor. In any case the prosauropods lower-quality food, yielding less energy per pound. do represent the transition from bipedal, carnivo- This in turn requires modifications of the teeth, rous saurischians to quadrupedal herbivores of the body, and digestive system to allow for the ade- same order. quate processing of a great quantity of plant food. In spite of the radical design changes that were nec- Ornithischian Dinosaurs essary, any dinosaur that could develop the proper adaptations for herbivory would have enjoyed a The ornithischian dinosaurs (order Ornithischia) great advantage in the early Mesozoic, when there are an amazingly varied assemblage of exclusively was little competition for the plant food in the early herbivorous types. The ornithischians come in all Mesozoic forests. Thus natural selection for plant- sizes, including armored and unadorned variet- eating inevitably produced the sauropod modifica- ies, quadrupeds and bipeds, and swift runners and tion of the original dinosaur body plan. cumbersome plodders. In fact, if we could view a One primitive group of dinosaurs, restricted to random sample of live ornithischian dinosaurs, we the early Mesozoic, seems to represent the transition would behold an array so heterogeneous that we from the swift carnivorous theropods to the lumber- might question why paleontologists assign all of ing herbivorous sauropods. This group is known as them to a single order. It is the structure of the pel- the prosauropods, regarded by most paleontologists vis, of course, that primarily unites all the ornithis- as the basal group (or infraorder) of the suborder chians. In all of these dinosaurs the pubis does not Sauropodomorpha. The earliest prosauropods were project forward and down, as it does in the sauris- small and bipedal; but as new forms developed dur- chians. Instead it lies parallel to the ischium, so that ing the late Triassic and early Jurassic, they become it extends from the region of the acetabulum (hip more fully quadrupedal. The overall build of most socket) down and to the rear (fig. A.3). In some of prosauropods is similar to that of the sauropods, but the later ornithischians, most notably the horned they were much smaller and less bulky. Two of larg- ceratopsians (e.g., Triceratops) and the armored est prosauropods, Riojasaurus and Plateosaurus, ankylosaurs, the pubis is shortened and develops were only 34 feet and 25 feet (11 and 8 meters) long, a forward projecting prong, but the basic ornithis- respectively. Other prosauropods were only about chian pattern is still discernable. This arrangement 10–15 feet (3.3 to 5 meters) long. The teeth of pro- of bones in the ornithischian pelvis is similar to the sauropods are generally spatulate in form and have pattern in modern birds, though most birds possess serrated edges that would have been well-suited a highly modified pelvis due to their adaptations for shredding plant food. It is certainly tempting to for flight. Remember, however, that the ornithis- view the prosauropods as the ancestor to the later chian dinosaurs are not closely related to birds, in sauropods, but this would probably be incorrect. spite of the name given to the order. As we have The prosauropods have only four functional toes in seen, it appears that the similarities in pelvic design their hind feet; the fifth digit is greatly reduced and between the modern birds and the ornithischian nonfunctional. True sauropods retain all five toes in dinosaurs have arisen from two independent evolu- their hind feet. It is unlikely that the fifth toe on the tionary events. The name Ornithischia has fostered Classification of Dinosaurs 251 a common misconception that these dinosaurs are ornithischian pelvis can be regarded as an adapta- the progenitors of the birds. It bears repeating that tion to herbivory. With the forward-pointing pubis the ancestors of the birds probably developed from folded back against the ischium, more space is avail- the earliest saurischian theropods and not from any able to house the larger digestive mass that process- of the ornithischians. ing plant food requires. Thus most of the features Aside from the distinctive structure of the pel- that distinguish the Ornithischia from the Sau- vis, the Ornithischia as a group share a few other rischia are related to the strictly plant-eating habits general characteristics. These shared characteris- of the former. tics seem to be related to the herbivorous diets of all Ornithischia is a much more diverse order than the members of this order. The rows of teeth in the the Saurischia, so the subdivision of this group of jaws of all ornithischian dinosaurs are inset, to one dinosaurs has been the subject of lengthy debate degree or another, toward the center of the mouth. among paleontologists. Though some contro- This inward location of the tooth rows gives the versy still persists, we now recognize four or five ornithischian a pronounced recess or “pocket” in major groups within the Ornithischia that are the cheek region. The cheek pocket probably served regarded as suborders or infraorders. Thyreophora as a food pouch and was used to hold masses of veg- (“shield bearers”), for example, is a subdivision of etation while it was being chewed. It is easy to imag- the ornithischian dinosaurs that includes the qua- ine what a typical ornithischian dinosaur such as drupedal armored types. It consists of two groups one of the “duckbill” types might have looked like possessing different types of armor: (1) the Stego- when feeding: leaves stuffed into the bulging cheek sauria, with large plates positioned vertically along pouches, the snout wrinkling with each stroke of the back and spikes located mostly on the tail, and the jaws, and the sounds of leaves being crushed or (2) the Ankylosauria, with heavy, flat-lying plates of sheared. Many ornithischians also possessed a wick- bone covering much of the body surface. Some of erlike network of bony rods (ossified tendons) laced the ankylosaurs were so thoroughly armored that along the backbone and the tail. These rods helped even their eyelids were protected by solid bone. to stiffen the tail and brace the backbone. Most The Ornithopoda (“bird-foot”) is a large subdivi- ornithischian dinosaurs thus had stiff tails, which sion of the Ornithischia that includes most of the helped to counterbalance and/or stabilize them bipedal varieties. The most familiar of the ornitho- while they were running, walking, or feeding. pods are the “duck-billed” dinosaurs, with their As a further adaptation for plant eating, the characteristically broadened snouts. There are many ornithischian dinosaurs all possessed a unique bone kinds of ornithopods, including some with elab- at the tip of the lower jaw: the predentary. The pre- orate bony crests on the head (such as the “snor- dentary supported a toothless bill (which looked kel-crested” Parasaurolophus), relatively primitive in many forms like an upside-down hoof) that was types such as Utah’s Camptosaurus and Tenonto- used to chop or pluck vegetation. Furthermore, the saurus, and even some small varieties such as Dry- joints between the tooth-bearing bones of the upper osaurus, which is also known from Utah localities. jaw were usually rather loose in ornithischians, While the ornithopods are most often described as allowing their jaws to pivot inward and outward as bipedal dinosaurs, the fingers of many of them bore they chewed. This movement permitted the lateral small hooflike claws, suggesting that they supported movement of the upper and lower tooth surfaces themselves in a quadrupedal posture at least occa- past each other. Such movement would have been sionally. In the Cretaceous period the Ceratopsia extremely efficient in grinding, shredding, and pul- (“horn-face”) became one of the most abundant and verizing plant matter. Even the restructuring of the diverse groups of ornithischian dinosaurs ever. The 252 Appendix ceratopsians are typified by their most familiar rep- emphasize that they are formal categories of classifi- resentative, Triceratops, which had three prominent cation with specific definitions. In discussing dino- horns and an enormous bony frill extending back- saurs we often use terms such as “tyrannosaurs” or ward from the posterior edge of the skull. The cer- “brachiosaurids” to describe a general type or group atopsians also had a well-developed “beak” used to of dinosaurs that may represent a specific taxo- chop and cut tough, low-growing vegetation. Cer- nomic category (such as a family) or might desig- atopsian dinosaurs have left mostly fragmentary nate a certain group of similar dinosaurs, without remains in the late Cretaceous strata of Utah, but reference to a formal category of classification (fig. their fossils are extremely abundant in rocks of this A.4). In instances of such informal use of names, the age in Montana, Canada, and Asia. Ceratopsian terms are not capitalized or italicized. bone beds in these places provide good evidence At the species level, in both paleontology and that these dinosaurs traveled across the ancient biology, we group together organisms so similar that landscape in gigantic herds. Pachycephalosauria reproduction between any two individuals of oppo- (“thick-headed reptiles”) is a rather bizarre group of site sexes would be possible. Different species of the ornithischian dinosaurs characterized by domelike same genus cannot interbreed, even though they heads, the result of the great thickening of the bones may look quite similar to us. Confirming repro- forming the roof of the skull. They also had blunt ductive viability, and therefore species validity, is a nodes or spikes around the edges of the their skulls, relatively easy task for the biologist studying mod- creating an even more peculiar appearance. Pachy- ern animals. We know, for example, that moun- cephalosaurs are not common in Utah but have tain lions (Felis concolor) cannot successfully mate been identified in abundance from Montana, Wyo- with house cats (Felis domesticus). Hence the two ming, Canada, and elsewhere. Because they shared felines are placed in separate species, although they an expanded and decorated margin of the skull with belong to the same genus because they are other- the ceratopsians, the pachycephalosaurs are some- wise very similar to each other. For dinosaurs, rec- times united with the horned dinosaurs in a group ognizing valid species is a bit more conjectural. known as the Marginocephalia. There is no way to be absolutely certain that Stego- saurus stenops (abbreviated S. stenops) could not have interbred with S. armatus. In addition, the lim- Dinosaur Genera and Species itations of the fossil evidence prevent us from know- Like other all other organisms, living and extinct, ing to what degree the soft tissues of S. stenops and the dinosaurs are placed into species and genera S. armatus were similar or different. So species in (plural of genus) at the lower levels of classifica- paleontology are established on the basis of much tion. Paleontologists generally refer to various dino- less complete information than the biologist uses to saurs by identifying only these two categories, even recognize groups of very closely related organisms though the complete pedigree would include all in the modern world. Dinosaur species are estab- the levels of classification. Thus Stegosaurus stenops lished on the basis of the similarity of skeletal fea- is a ornithischian dinosaur (of the group Thyreo- tures represented by preserved bones and teeth. As phora) that belongs to the genus Stegosaurus and we have already learned, this aspect of dinosaurs is the species stenops. By convention the genus name rarely known in its entirety. is always listed first and capitalized, while the spe- Some genera include several species, while others cies name follows in lowercase. Both genus and spe- only have one. Because of the fragmentary nature of cies names are usually italicized or underlined to the fossil record, paleontologists must often attempt Classification of Dinosaurs 253

A.4. The relationships and stratigraphic range of some of Utah’s dinosaurs. The chart is not complete, for it emphasizes only the best-known dinosaurs. A complete phylogeny (family tree) would require much more space. to identify dinosaur species and genera on the basis adults) of the same species. In addition, some spe- of very little and/or poorly preserved material. Con- cies of dinosaurs are based on meager fossil infor- sequently it is not surprising that some dinosaur mation (a single tooth fragment, for example). species are controversial and that debates persist These may be invalidated at a later time by the dis- about which dinosaur species are valid and which covery of more complete skeletons. Another fac- are not. Sometimes new discoveries cause us to reas- tor that contributes to our confusion is that we sign a species to a new genus, abandon some species can never be absolutely certain what the range in that prove to be invalid, or otherwise restructure variation within a species was without having the the classification to accommodate new information. entire population available for study. Without this This aspect of dinosaur classification will always information determining the degree of similarity exist, and there will always be some uncertainty required for different fossils to be assigned to a sin- about the lower levels of taxonomy. gle species is always a matter of individual judg- It may be that many of our named dinosaur spe- ment and interpretation. Though paleontologists are cies, presently numbering over 800, are invalid currently making great progress in recognizing the because they actually represent, for example, males range of variation within some dinosaur species (see and females or different growth stages (juveniles or Carpenter and Currie 1990), the scrappiness of the 254 Appendix fossil record will never allow us to know it all. These uncertainty that will always exist at the species level. uncertainties generally become less severe as we Currently about 500 genera of dinosaurs have been ascend the hierarchy of classification from the spe- established by paleontologists (Wang and Dod- cies level to the genus, to the family, and so on. This son 2006). This number is subject to change in the is another reason for concentrating on the genus future, as some genera will be combined or aban- level in our study of Utah dinosaurs. In so doing doned, while new genera are established to accom- we can avoid at least some of the confusion and modate new discoveries. References

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Note: all geographic locations are in Amphicoelias, 96 Ash, S. R., 60 Utah unless otherwise indicated. analcime, 80 ash layers, and volcanoes during anatomical bias, in fossil record, Mesozoic, 15–16 Absaroka thrust system, 212 20–21 Asilisaurus, 27 Abydosaurus mcintoshi, 160–61 angiosperms, in early Cretaceous, asteroid impacts: evidence for during Acristavus gagslarsoni, 192–93 165–66. See also plants Mesozoic, 11–12; K-T interval and Acrocanthosaurus, 165 Animalia, 246 extinction of dinosaurs, 227, 231 adaptive radiation, 46, 47 Animantarx, 161, 162 Atlantic Ocean, 31, 170 aetosaurs, 25, 38–39, 65–66 Ankareh Formation, 29 Atlantosaurus, 92–93 Africa: and Barosaurus, 96; climatic ankles, and skeletal features of Atreipus, 40, 41 oscillations and migrations on dinosaurs, 244–45 Avemetatarsalia, 245 savannahs of east, 83, 85; and Ankylopollexia, 111 Avisaurus archibaldi, 204–5 Massospondylus, 63; and origins Ankylosauria, 110–11, 161, 251 Aztec Sandstone, 51 of dinosaurs, 27; and predator/ Anomoepus, 58 prey ratio on savannahs of anoxia, and deep circulation of badlands, 33–34, 75 east, 130. See also Tendaguru oceans, 48 ball-and-socket joints, of Formation Anthracospirifer, 2 Torvosaurus, 134 age: and horns of ceratopsians, 224; Apachesaurus, 37 Baptornis, 177 and identification of species of Apatosaurus, 88, 90, 92–94, 110, 248, Barosaurus, 94–96, 249 dinosaurs, 253 249 Barremian age (Cretaceous), 158 “Age of Mammals,” and Cenzoic, 3 ajax, 94 Basilemys, 215 “Age of Reptiles,” and Mesozoic, excelsus, 94 Bathyurellus, 2 5. See also “Golden Age of louisae, 94 Batrachopus, 56 Sauropods” A. yahnahpin, 94 beak: of ceratopsians, 191; of Alamosaurus sanjuanensis, 216–20, apomorphic skeletal features, 25 Ornithomimidae, 139; of 224, 226, 233, 249 Aralia, 3 Stegosaurus, 106; of Triceratops, Alaska, 130, 170 Arapien Shale, 70, 72 221, 252 Albertosaurus, 225, 226 Araucarioxylon, 36 Bear River Range, 179 Allosauridae, 126–33, 248 Archaeological Resources Protection behavior. See ambush; Allosaurus, 108, 137, 248 Act of 1979, 240 communication; herds A. fragilis, 126–33 Arches National Park, 72 and herding; migrations; amateurs, and vertebrate Archibald, J. D., 227, 228, 229 reproduction; social organization paleontology, 238–39 Archosauria and archosaurs, 26, 247 Belcher, C. M., 48 ambush: and Deinosuchus, 207; and Argentinosaurus, 219 Benton, M. J., 227 group hunting by therapods, 131 Arizona, and evidence for dinosaurs bentonite, 15, 16, 33–34, 80 ammonites, 5. See also Scaphites in Chinle Formation, 42–44 Berlin-Ichthyosaur State Park Ammosaurus, 68 Arizonasaurus, 29–30 (Nevada), 28 amphibians: and early Cretaceous, armor: of Gastonia burgei, 154; Berman, David, 92 167–68; and early Triassic, 29; and of ornithischians, 106, 251; of biases, in dinosaur fossil record, late Triassic in Chinle Formation, Scutellosaurus, 65; of Stegosaurus, 20–22, 119 37; and Morrison Formation of 107 Big Indian Rock, 60 Jurassic, 141; and Paleozoic, 4 Arrhinoceratops, 221–22 biotic stress, and K-T event, 233

283 284 Index biotite, 16 Bureau of Land Management, viii, Cedar Mountain Formation, 13, 144, birds: and Avisaurus, 204–5; and 130, 189, 239 145, 148, 149–50, 158–69 classification of dinosaurs, Burge, Don, 149, 152 Cedarosaurus weiskopfae, 157–58 247; dinosuarian ancestors Burro Canyon Formation, 144 Cedarpelta, 161 of in early Mesozoic, 6; and Cedrorestes, 156 Morrison Formation of Jurassic, Cadoceras, 5 Central America, and migration of 141; and Ornithischia, 250–51; calcareous mudstones, 145 dinosaurs between North and and Ornithomimidae, 201; and calcite, 145 South America, 220 Tetanurae, 125; and tracks in calcium carbonate, 19 Centrosaurinae, 192 Kayenta Formation, 58. See also caliche, 145 Cenzoic era: as “Age of Mammals,” 3; emu; ostrich; seabirds Camarasauridae, 97–102, 249 formal subdivisions of, 210 Bistahieversor, 205 Camarasaurus, 92, 98–100, 101, 102 Ceratodus, 37, 56 Bjork, P. B., 155 C. grandis, 100 Ceratopsia and ceratopsians, 190–91, Blackhawk Formation, 183, 185, 187 C. lentus, 98, 100 193–95, 208, 220, 224, 251–52. See black market, for dinosaur C. lewisi, 100, 102 also Triceratops fossils, 240 C. supremus, 100 Ceratosauria, 42, 62, 121, 248 “black shale,” 9 Cameron Member, 35 Ceratosaurus, 109, 130, 248 Blakey, Ronald, viii camouflage, of Camptosaurus, 113. C. dentisulcatus, 125 Bodily, N. M., 149, 154 See also skin impressions C. magnicornis, 125 body size, estimates of for dino- Campanian age (Cretaceous), 185, C. nasicornis, 123–25 saurs, 21 207–8 cervical vertebrae: of Coelurus, 138; bogs, and Cleveland-Lloyd Quarry Camptosauridae and camptosaurs, of diplodocids, 86, 93. See also as “predator trap,” 131, 132–33 84, 111–14 neck; vertebrae Bonis, N. R., 48 Camptosaurus, 112–13, 251 Cetiosauridae, 104–5 Book Cliffs, 13, 172, 183 C. amplus, 113 Characichnos, 57 Boulder Mountains, 214 C. aphanoecetes, 113 Chasmosaurinae, 192 Brachauchenia, 174 C. dispar, 113 cheek pockets: of Camptosaurus, Brachiosauridae, 102–4, 249 Canaan Peak Formation, 185, 213, 214 112; of iguanodontids and Brachiosaurus altithorax, 102, Capitol Reef, 1 camptosaurids, 112; of 103, 249 Capitol Reef National Park, 143, 214 Ornithischia, 251 Brachychirotherium, 41 carbonaceous sediments, in Cedar chert, 79, 147 braided river systems, 53, 79 Mountain Formation, 167 chevron bones, in tail of brain case, of Troodontidae, 140 carbon cycle, disruption of at end of Camarasaurus, 99 Brasilichnium, 58 Triassic, 47–48 Chindesaurus, 43 Brest van Kempen, Carel, viii Carbon County, 184–85 Chinle Formation: ecosystem and Brigham Young University, 103, 149, carbon dioxide: concentration of nondinosaur fossils of, 35–39; and 216, 241 atmospheric during Triassic- evidence for dinosaurs from New Britt, B. B., 133–34, 138, 139, 154 Jurassic extinctions, 48; increase Mexico and Arizona, 42–44; and Brontosaurus. See Apatosaurus of in Mesozoic atmosphere, 9, 11 evidence for early dinosaurs from brow horns, of ceratopsians, 191. See Carmel Formation, 70, 71, 72, 73 Utah region, 39–42; and first also horns Carnosauria, 120, 126–35 appearance of dinosaurs in North brow ridges: of Allosaurus,, 127; of Carpenter, Kenneth, 108, 110, 111, 116, America, 28; geology of, 32–35 Ceratosaurus, 124 137, 149, 156 Chinle Trunk River, 32–33 Brushy Basin Member, 14, 77, 78, Castle Dale, 162 Chirostenotes, 203 80–81, 85, 100, 126, 128, 143 Castlegate Formation, 183, 185 Church Rock Member, 33, 34, 35, 41 Bryce Canyon, 173 Castle Valley, 172 Chure, Daniel J., 113, 138, 140 Buckhorn Conglomerate Member, cat (Felis domesticus), 252 Cifelli, Richard L,, 148, 149–50 , 154 144, 147 cataloging, of prepared fossils, 237–38 Cionichthys, 37 Buettneria, 37 caudal vertebrae, of Alamosaurus, Circle Cliffs, 35, 212, 214 Bull Canyon Formation, 44 217–18. See also vertebrae clades, 24–25 Index 285 cladistics, 24–25, 121, 155. See also 196–97; and Diplodocus herds, Moenave Formation, 56. See also classification; taxonomy 88, 91 molluscs cladograms, 24 Compsognathus, 21, 248 Crystal Geyser Quarries, 149 classification: of dinosaurs, 243, 246– conglomerates, 181, 214. See also CT-scanning devices, 238 54; of theropods, 120–21. See also Buckhorn Conglomerate Curtis Formation, 70, 72, 73 cladistics; taxonomy Member; Shinarump cycads, 84 Cleveland-Lloyd Dinosaur Quarry, Conglomerate cynodonts, 26 16, 81, 105, 112, 126, 129–33, 236, conifers, of late Triassic, 36. See also Cynognathus, 6 238, 242 plants Czerkas, S. A., 108 climate: and Campanian age fauna, continental drift. See plate tectonics 208; change in Utah at end of convergent evolution, 26 Dakota Formation, 170–71, 185 Cretaceous, 209; and drought Cope, Edward D., 96 Dalton Well Quarry, 146, 149, 150, cycles in Jurassic, 132–33; and K-T coprolites, and fossil record, 18 152, 236–37 extinctions, 215, 233; of Mesozoic, Corythosaurus, 111, 196 Daspletosaurus, 205 8; of middle Jurassic, 71–72; rapid Crawford Mountains, 179 DeBlieux, D. D., 192 change in and extinctions at crests: and Dilophosaurus, 62; and decomposition, and process of Triassic-Jurassic boundary, 48; of Parasaurolophus, 196–97 fossilization, 18–19 Triassic, 23–24; of Utah at end of Cretaceous: boundary with Jurassic Deep Creek Range, 70, 76 Cretaceous, 212; of Utah in late in sedimentary sequences of defense: herding behavior as, 94; Jurassic, 82, 85. See also global Colorado Plateau, 143; and and plates of Stegosaurus, 107–8. warming; greenhouse effect; dinosaur faunas of Cedar See also armor seasonality Mountain Formation, 149–69; deflation basins, and sandstone clinoptilolite, 80 dinosaur faunas of southern deposits, 52 Clioscaphites vermiformis, 5 and southwest Utah in late, 188– deformation, and Sevier Orogenic Cloverly Formation (Montana), 89; and dinosaurs of Straight Belt, 180 159, 164 Cliffs-Wahweap-Kaiparowits Deinonychus, 139, 152, 164 coal: and Cedar Mountain Sequence, 189–209; east-central Deinosuchus, 206–7 Formation, 166; and Mesaverde Utah during early, 143–49; faunal DeLafosse, Peter, vii, viii Group, 184–85, 186; and North transition during early, 169– dermal ossicles, 110 Horn Formation, 215 71; and main phase of Sevier Desmatosuchus, 25, 39 coastal dunes, in middle Jurassic, 72 Orogeny, 178–80; and Mancos Diabloceratops eatoni, 190, 192 coastal oscillation, cycles of during Sea, 172–78; Mesaverde Group Diapsida, 24, 247 Triassic, 29 and dinosaurs of late, 183– DiCroce, T., 156 coastal plain, of Western Interior 88; Sevier foreland basin and dicynodonts, 26, 38, 39 Seaway, 181–83, 207 dinosaurs of late, 180–83; unusual digging, by fauna in Wahweap coelacanths, 5 global climatic conditions and Formation, 193 Coelophysis, 42–43, 123, 248 oceanic circulation during, 9; digitigrade condition, and ankles of Coelurosauria, 120, 126, 135–42 volcanic activity and end of, 231, dinosaurs, 245 Coelurus, 137–38 233. See also K-T interval Dilophosaurus, 47, 56, 61–62, 123, 248 Colbert, Edwin H., 42 Crichton, Michael, 120 Dinnetherium, 61 collaboration, in paleontology, 235 crocodiles: and Chinle Formation, Dinochelys whitei, 141 collecting bias, in fossil record, 21 38; classification of, 247; and dinosaur(s): in Chinle Formation of College of Eastern Utah, 149, 225 Morrison Formation, 141; and late Triassic, 39–44; classification color, of ceratosaurs, 123. See also skeletal features of dinosaurs, 245, of, 243, 246–54; definition of, 243, skin impressions 246. See also Deinosuchus 244–46; early forms of in North Colorado River, 159 Crocodilia, 247 America during Triassic, 28, 31; Comb Ridge, 48 cross-beds, in sand deposits, 51–52 and fauna of Cedar Mountain communication: and ceratopsians, Crurotarsalia, 245 Formation, 149–50; and fauna 224; and crest of Parasaurolophus, crustaceans, and Lake Dixie in of Kayenta Formation during 286 Index

Jurassic, 61–66; and fauna of dry washes, in desert environ- erosion: and Cedar Mountain Morrison Formation in late ments, 52 Formation in early Cretaceous, Jurassic, 86–119; and fossil duck-billed dinosaurs. See 147–48; and fossil record in Utah, record in Utah, 16–22; fossils hadrosaurs; Ornithopoda and 19; of Mesozoic formations in from Navajo Sandstone and ornithopods Utah, 14 life in sand sea, 66–69; and late dune fields, and sandstones of early Escalante Petrified Fossil State Cretaceous in southern Utah, Jurassic in Utah, 50–52, 53 Park, 82 188–89; and Maastrichtian age, Dystrophaeus, 96 Eubrontes, 56, 57, 58 210; of Mesaverde Group, 185–88; Dystylosaurus, 249 Euparkeria, 27 of North Horn Formation, 216– Europe: earliest presence of 27; origins of in Triassic, 23–27; East African Rift, 23 dinosaurs in, 27; and fauna of and Sevier foreland basin in late Eastern Prehistoric Museum (Utah Cedar Mountain Formation, Cretaceous, 180–83; success of State University), 242 158; and global geography during Mesozoic and mystery Eaton, J. G., 150 in early Cretaceous, 169–70; of subsequent extinctions, 227– Echo Canyon, 13 and Scelidosaurus, 65; and 33; surge of new discoveries ecosystems: and Lake Dixie in titanosaurids, 219 about, vii–viii; and volcanoes in Moenave Formation, 56; Evanston Formation, 213 Mesozoic landscapes of Utah, and nondinosaur fossils of evolution, Mesozoic as time of 15–16. See also eggs and eggshells; Chinle Formation, 35–39. experimentation in, 3. See also footprints and trackways; fossils See also landscape; terrestrial adaptive radiation; convergent and fossil record; paleontology; environments evolution; natural selection; skin impressions Edmontosaurus, 111, 226 specialization Dinosauria, 120 Effigea, 43 excavation, of fossils, 235–37 Dinosaur National Monument, 19, eggs and eggshells: of Allosaurus, expeditions, as phase of 40, 41, 81, 92, 95, 99, 100, 112, 116, 133; of Dryosaurus, 116; and paleontology, 235 126, 133, 146, 159, 160, 238, 242 fauna of upper Cedar Mountain extinctions: of late Paleozoic, 3–4; in Dinwoody Formation, 28 Formation, 168; and fossil record late Triassic, 46–48; of sauropods Diplodocidae, 86–97 in Utah, 17; and North Horn in western North America, 220; diplodocids. See sauropods Formation, 224–25 success of dinosaurs during Diplodocus, 86, 87–88, 89, 91–92, 249 Elaphrosaurus, 139–40 Mesozoic and mystery of at end D. carnegii, 88 elephants, 247 of Cretaceous, 227–33 D. hayi, 88 Elosaurus, 92–93 eyes, of Troodontidae, 140–41 D. lacustris, 88 Emery County, 185 D. longus, 88 Emery Uplift, 81–82 Faberophyllum, 2 Dipnoi, 37 employment, of professional fabrosaurids, 111 disease epidemics, and dinosaur paleontologists, 241 Falcarius utahensis, 150, 151 extinctions in terminal emu, 139 feathers, and oviraptorosaurs, 203 Cretaceous, 233 enantiornithines, 205 feet, and skeletal features of Dixie, Lake, 53, 54, 56–57, 60 Entrada Formation, 70, 71, 72 dinosaurs, 244, 245. See also foot Dixie State College, vii Entrada Sandstone, 13 claws; hands DNA sequencing techniques, 238 Entradasuchus, 72 femur, and skeletal features of Dockum Formation, 28 Eolambia caroljonesa, 162–63 dinosaurs, 244, 245 dolomite, 145 Eopneumatosuchus, 61 ferns, 84, 166. See also plants Doyle, Arthur Conan, 120 Eopolycotylus, 174 Ferron (town), 13 Drinker nisti, 118–19 Eoraptor, 26 Ferron Sandstone, 185, 188 Dromaeosauridae, 138–39, 152, 163– Epanterias, 133 fingers, of therizinosaurs, 151. See 64, 248 epaxial osteoderms, of Ceratosaurus, also hands Dromomeron romerii, 43 124 Fiorillo, A. R., 100 Dryosaurus, 115–16, 117, 118, 251 ephemeral lakes. See playa lakes “first-order bounding surfaces,” and Dry Mesa Quarry (Colorado), 102– ergs, and sandstones of early Jurassic eolian sandstones, 52 3, 133 Utah, 50–53 fish: and diet of Deinosuchus, Index 287

207; and K-T extinctions, 230; 194–95, 224; of Torosaurus, 222; of Glen Canyon Group, 14, 48, 49, 52, and Lake Dixie in Moenave Triceratops, 220, 252 53–61 Formation, 56; and Mancos Sea, Futalognkosaurus, 219 global warming: in Cretaceous, 11; in 174; of Mesozoic, 5; and Morrison Mesozoic, 8. See also climate Formation, 141; and North Horn Galton, P. M., 118, 133, 139, 155 Glyptops plicatus, 141 Formation, 214; of Triassic in Gargoyleosaurus, 111 Goblin Valley, 30 Chinle Formation, 37. See also Gaston, R., 153 Godzilla movies, 105–6 sharks Gastonia burgei, 154 “Golden Age of Sauropods,” 86, 119 fission-track dating, of volcanic ash, Gaston Quarry, 146, 149, 150, 152, Gondwana, 7 143 154, 238 Gorgosaurus, 205 Flaming Gorge Reservoir, 73 gastroliths: and Cedar Mountain Graffam, Merle, 177 flash floods, in desert environments, Formation, 144–45; and fossil Grallator, 40–41, 56, 57 52 record in Utah, 17–18; and Grand County, 150 flying, and Avisaurus, 205 prosauropods, 63; and sauropods, Grand Staircase-Escalante National foot claws: of dromaeosaurs, 163; of 91–92 Monument (GSENM), vii, 189, Utahraptor ostrommaysi, 152, 153. Gates, T. A., 192 194, 197, 203, 206, 238, 242 See also feet Gauthier, J., 120–21, 135 Grapevine Wash Formation, 213 footprints and trackways: and Geminiraptor suarezarum, 151–52 grass, and African savannahs, 83. See fossil record in Utah, 17; from gender. See sexual dimorphism also plants Glen Canyon Group, 54, 57–58; genus, and classification of Greenhalgh, B. W., 158 of hadrosaurs in Kaiparowits dinosaurs, 252–54. See also Greenhorn Cycle, 170–71 Formation, 199; of iguanodonts, ichogenus greenhouse effect, and Mesozoic, 11. 164; and Kayenta Formation, geochemistry, and K-T boundary, See also climate 58; and Mesaverde Group, 185– 229 Green River, 150 88; and Moenkopi Formation, geography: early Cretaceous and groups, and geologic formations, 14. 30–31; Morrison Formation and changes in global, 169–70; of See also Mesaverde Group migrations during late Jurassic, Mesozoic, 6–8; of Triassic, Gryposaurus, 188 85, 91; and Navajo Sandstone, 23–24. See also landscape; G. monumentensis, 197–98 58–59, 66; and San Rafael Group North America; ocean(s); plate Gulf of Mexico, and K-T event, 231 during middle Jurassic, 72–74; tectonics; rivers; South America Gunnison thrust system, 212 and traces of dinosaurs in Chinle geology: and early Jurassic rock Formation, 39–41 sequence of Utah, 48–53; and habitat bias, in fossil record, 20 formation: boundaries between K-T boundary, 210–11; Mesozoic hadrosaurs, 177, 187, 195–201, 221 successive, 13; definition of, 12–13; and rock record of Utah, 12–14; Hagryphus giganteus, 202–3 naming of, 13; subdivision of into of Morrison Formation in late Hall, Dee, 133 smaller sequences or intervals, Jurassic, 76–82; and rocks of mid- hands: of Ornitholestes, 136; and 14. See also Chinle Formation; Jurassic San Rafael Group, 70–72; skeletal features of dinosaurs, Morrison Formation of Utah in early Triassic, 28–31; 245–46; of Utahraptor, 153. See fossils and fossil record: black and volcanism during Mesozoic, also feet; fingers market for, 240; cataloging 10–12. See also conglomerates; Hanksville Basin, 13 of, 237–38; excavation of, 235– erosion; formations; groups; Hanksville-Burpee Quarry, 81, 95, 37; nondinosaur fossils in limestone; members; mudstones; 238 Chinle Formation, 35–39; and plate tectonics; sandstones; Sevier Haplocanthosaurus, 104, 105 preparation laboratory, 237; and Orogenic Belt; unconformity; H. delfsi, 105 process of fossilization, 16–22; volcanoes and volcanic activity H. priscus, 105 sources of bias in, 20–22, 119. Ghost Ranch Quarry (New Mexico), Heaton, J. S., 143 See also dinosaurs; mammals; 42 Hell Creek Formation, 228, 229, 231 paleontology Gillette, David, 91–92, 96 Hemicalypterus, 37 Franciscan complex, of California Gilmore, C. W., 216, 221, 222, 224, 225 Henry Basin, 82 Coast Ranges, 82 gizzard, of sauropods, 91. See also herds and herding: and frill: of ceratopsians, 191–92, gastroliths Camptosaurus, 113; of 288 Index

ceratopsians, 192, 224, 252; ischium, and classification of laboratory, and preparation of communication and social dinosaurs, 247, 250 fossils, 237 structure of sauropods, 88, 91; as Lacertipus, 58–59 defense for sauropods, 94; and jackets, and excavation of fossils, 236 lakes. See Dixie, Lake; playa lakes; Falcarius, 151; of hadrosaurs, 187, Jensen, James A., 133, 149, 155, 196, Powell, Lake 199. See also migrations 216, 224 Lakota Formation (South Dakota), Herrerasaurus, 23 Johnson, Sheldon, 54 158 Hesperornis, 177 Jurassic: boundary with Cretaceous Lambeosaurinae, 196 Hesperosaurus mjosi, 110 in sedimentary sequences of landscape: and geography of Hesperosuchus, 39 Colorado Plateau, 143; and Mesozoic, 6–8; and Mussentuchit Hippodraco scutodens, 156–57 extinctions at Triassic-Jurassic Member in Utah, 167; of Utah historical bias, in fossil record, 119 boundary, 48; and fauna of in late Jurassic, 78–86. See also Hoplitosaurus, 149, 154 Kayenta Formation, 61–66; geography horns: of ceratopsians, 192, 195, and footprints from San Rafael Langston, W., 159 224; of Ceratosaurus, 123–24; of Group, 72–74; fossils from Navajo Laramide Orogeny, 212–13 Torosaurus, 222; of Triceratops, Sandstone and life in sand sea, Laramidia, 179, 180, 208 220, 252. See also nose horns 66–69; geology of Morrison Laurasia, 7, 23, 31, 32 horse, 245 Formation and landscape of lava, 10–11 House Range, 70, 76 Utah in late phase of, 76–86; Lawson, T. F., 222–25 Howe Quarry (Wyoming), 88 as “Golden Age of Sauropods,” Lepidosauria, 24, 247 Hunt, A. P., 186 218; marine transgression in Leptoceratops, 226 hunting, and behavior of therapods, Utah during middle, 69–70; and library research, and paleontology, 131. See also ambush; predators new array of dinosaurs in Glen 235 Hurricane Mesa, 35 Canyon Group, 53–61; and rocks limestone, 214, 215 Hypsilophodon, 21 of San Rafael Group in Utah, Lisbon Valley, 37 Hypsilophodontidae and 70–72; rock sequence of Utah in Lissodus johnsonorum, 56 hypsilophodontids, 111, 114–18 early, 48–53; and theropods of Lithostrotian, 2 Morrison Formation, 121–41 lizards: and Cedar Mountain ichnofauna, 66, 72 Jurassic Park (movie 1993), 120, 138, Formation, 168; and Morrison ichnogenus, 40 152 Formation, 141; and North Horn ichnospecies, 40 Formation, 215; and skeletal Ichthyornis, 175, 176, 177 Kaiparowits Formation, 183–84, 193– features of dinosaurs, 245, 246, ichthyosaurs, 244 209 247; of Triassic, 26. See also igneous rock, 10–11 Kaiparowits Plateau, 183 reptiles Iguanacolossus fortis, 156 Kayenta Formation, 48, 53, 58, 61–66 Lloyd, Malcolm, 130 Iguanodon, 114 Kayentatherium, 61 Loch Ness monster, 174 I. ottingeri, 155 Kirkland, James I., vii, 57, 61, 111, 148, Lockley, M. G., 186 Iguanodontidae, 111–14, 155–56 149, 151, 153, 154, 162, 192 Loewen, M. A., 67 ilium: and classification of dinosaurs, Kokopelia juddi, 168 Long Walk Quarry, 146, 149, 158, 159 247; of Stokesosaurus, 135 Koparion douglassi, 140–41 Lost World (Doyle 1914), 120 illite, 145 Kosmoceratops richardson, 193, 194– Lost World, The (Crichton 1995), 120 infraorders, and classification of 95, 208 Lucas, S. G., 175 dinosaurs, 246 Kowallis, B. J., 143 lungfish, 37 insects, and Morrison Formation, Kritosaurus, 177, 198, 199, 226 141 K-T interval: dinosaur extinctions Maastrichtian age (Cretaceous), intelligence, of Troodontidae, 140 and study of, 227–33; interest of 208–9, 210, 213, 215, 218 interdune areas, and playa lakes, 52 geologists and paleontologists Macomb Expeditions (1859), 96 International Commission on in, 210–11; and North Horn Madsen, J. H., 125, 127, 128, 130, 134, Stratigraphy, 210 Formation, 213–17; use of term, 135, 138, 148 iridium, 229, 231 210; in Utah, 211–13 magnetic field reversals, 10, 216 iron oxides, 19, 23 mammal(s): and Cedar Mountain Index 289

Formation, 168; and extinctions Metoposaurus, 25 Nanosaurus, 118–19 in late Triassic, 47; of Ice Age migrations: and landscape of National Natural Landmarks, 130 in La Brea tar pits, 132; and Morrison Formation, 83, 84–85; National Park Service, 239 Kayenta Formation, 61; and by sauropods during late Jurassic, Native Americans, and reservations late Cretaceous in Utah, 190; in 91; by sauropods from South in Utah, 240 Mesozoic, 5–6; and Morrison America in Maastrichtian, 219. natural selection, and theropods, 120 Formation, 141–42; and See also herds and herding Navahopus, 59 Mussentuchit Member, 167; and Miller, W. E., 130 Navajo Sandstone, 48, 49–50, 51–52, North Horn Formation, 215–16; Milner, Andrew, 57, 61 53, 58–59, 66–69 and social organization of herds, Mississippi, swamps and bayous of, neck: of Allosaurus, 128; of 88, 94. See also cat; elephant; 185 Barosaurus, 94–95; of horse; porcupine; sloths; Moab megatracksite, 72–73 brachiosaurids, 102; of tritylodonts Moenave Formation, 53, 54, 55, 60 Camarasauridae, 97; of Mammalia, 247 Moenkopi Formation, 28, 29, 30–31, Camarasaurus, 98, 100; of Mammenchisaurus, 249 32 Camptosaurus, 112; of ceratosaurs, Mancos Sea, 172–78 molds and casts, and fossil record in 122, 124; of cetiosaurids, 104; of Mancos Shale, 9, 172–73, 174, 175, Utah, 19 diplodocid sauropods, 86, 90, 91; 177, 182 molluscs, 173, 215 of Torvosaurus, 134 Maniraptora, 136, 151, 201, 203 Molnar, R. E., 134 Nedcolbertia, 153 Mantell, Gideon, 114 Monitor Butte Member/Formation, Nelson, M. E., 150 Marsh, Othniel C., 92, 115, 118, 120, 35 Neslen Formation, 183, 187 126 Montana State University, 222 neural spines: of Allosaurus, Marshosaurus, 130 montmorillonite, 131, 145 128; of Apatosaurus, 93; M. bicentesimus, 138–39 Monument Uplift, 81–82 of brachiosaurids, 102; of “mass extinction,” and K-T event, Morales, M., 60 Camarasauridae, 97; of 230, 231 Morganucodon, 61 cetiosaurids, 104, 105; of Massospondylus, 63–64, 68 Morosaurus, 98 diplodocid sauropods, 87, McDonald, Andrew, 156 Morrison Formation, 15, 75: and 88; of Saurophaganax, 133; of McIntosh, John, 92, 102 Cleveland-Lloyd Dinosaur Seismosaurus, 97 Megalosauridae, 133–34 Quarry, 16; dinosaurs of, 86–119; Nevadan Orogeny, 82 Megapnosaurus, 56, 62–63 geology of, 76–81; and landscape Newark Rift, 23 members, as subdivisions of of Utah, 81–86; members of Newark Supergroup, 28 formations, 14 in Utah exposures, 14; and Newberry, John S., 96 Mesaverde Group, 183–88 theropods, 121–41; unconformity New Mexico, 42–44 Mesocordilleran High, 31–32, 70, at top of, 143–44 nitrogen cycle, disruption of at end 76–77, 81–82, 146 Mossback Member, 33, 34, 35 of Triassic, 47–48 mesotarsal ankle, 245 mountain lion (Felis concolor), 252 nodosaurs, 153–54 Mesozoic: as “Age of Reptiles,” 5; Mowry Shale, 174 Norman, D. B., 155 asteroids and meteorites in, 11–12; mudstones, 80, 130–31, 144, 145 North America: early dinosaurs climate of, 8; eastern Utah as multituberculates, 141–42 during Triassic, 28; and global natural museum of, 1–2; life of, Mummy Cliffs, x, 1, 35 geography in early Cretaceous, 3, 5–6; geography and landscape Museum of Comparative Zoology 169–70; and land bridge to South of, 6–8; geology and rock record (Harvard University), 60 America in late Mesozoic, 220 of in Utah, 12–14; and oceans, Museum of Natural Science (Weber North Horn Formation, 213–27 8–10; as time of evolutionary State University), 242 North Horn Mountain, 185 experimentation, 3, 4; use of Museum of Northern Arizona, 60, nose horns: of ceratopsians, 191; of term, 2; volcanism and geology 177 Ceratosaurus, 124. See also horns of, 10–11 Mussentuchit Member, 148, 150, 158– Nothronychus graffami, 177–78 Metaposaurus, 37 69 Nugget Sandstone, 51 meteorites. See asteroid impacts Mymoorapelta maysi, 111 numerical quality, of fossil record in methane, and volcanic eruptions, 11 Utah, 18–20 290 Index oases, and sandstone deposits, 52 and classification of theropods, Formation, 165–66; and Kayenta ocean(s): disruption of deep 120; institutions and Formation, 61; of Mesozoic, 5; circulation near Triassic-Jurassic organizations in Utah with active and Morrison Formation, 82–84; boundary, 48; and extinctions programs in, 241–42; and K-T and North Horn Formation, 215; of late Triassic, 46; global boundary, 210–11, 229; and new and Straight Cliff Formation, 190 regressions in Maastrichtian dinosaur array of Glen Canyon Plateosaurus, 250 age, 211–12; of Mesozoic, 6, Group, 53–61; preparation for plate tectonics: of Mesozoic, 7–8; 8–10; regressions and Sevier career in, 240–41; process of, and Sevier Orogeny, 179–80; of Orogenic Belt, 181; transgression 234–40; and recent research in Triassic, 31, 32 in early Cretaceous, 167; and Utah, vii–viii. See also dinosaurs; playa lakes, 52, 80, 82 transgressions in Utah in Jurassic, fossils and fossil record plesiomorphic skeletal features, 25 52, 69–70. See also Atlantic Paleontology Volunteer Certificate plesiosaurs, 174, 177, 244 Ocean; coastal plain; Mancos Sea; Program, 239 pleurocoels: of Alamosaurus, 218; of sea level; Western Interior Seaway Paleozoic: extinctions of late, 3–4; Camarasaurus, 98; of sauropods ocean ridges, 10 fossils of, 2–3 from Long Walk Quarry, 159 Office of the Utah State Palmulasaurus, 174 Pleurocoelus, 159–60, 163 Paleontologist, vii, 239–40, 242 Pangea, 6–7, 8, 11, 23, 31, 71 pliosaurs, 174 Oklahoma Museum of Natural Panthalassa, 6, 8 pneumatic pockets, and theropods, History, 149–50 Paradapedon, 25, 26 43 Ontong-Java Plateau, 10 Parasaurolophus, 111, 188, 195–96, Poison Strip Sandstone, 148, 150, 158, Ornithischia and ornithischians, 64, 200, 251 169 105–10, 247, 248, 250–52 P. cyrtocristatus, 196, 197 Polacanthus, 154 Ornithodira, 24 P. walkeri, 196, 197 Polyglyphanodon, 215 Ornitholestes, 121, 136–37 Paronychodon, 164 “popcorn” surface, of bentonitic Ornithomimidae, 139–40, 248 Pawpawsaurus, 163 mudstone, 15 Ornithomimus velox, 201–2 Peloroplites cedarimontanus, 161 Popo Agie Formation (Wyoming/ Ornithopoda and ornithopods, 85, pelvis: of Allosaurus, 128; and Idaho), 29 111–19, 155, 162, 251 classification of dinosaurs, 247, porcupine, 110 ossified tendons, and ornithischians, 248, 250, 251; of therizinosaurs, Postosuchus, 25 251 151 Powell, Lake, 40, 41 ostrich, 139 Pentasauropus, 41 predators: and Cleveland-Lloyd Ostrum, J. H., 137 Pereda-Suberbiola, J., 154 Quarry as “predator trap,” 132; Othnielia, 118 Permian, and extinction event, 4 and Kaiparowits Formation, 201– Othnielosaurus, 118 permineralization, 19 7; and predator/prey ratio, 130. Otozoum, 59 Permo-Triassic extinction, 4 See also theropods oviraptorosaurs, 202–3 Petrified Forest Member, 33, 34, 35, predentary, of ornithiscians, 251 Owen, Richard, 243 36 prey. See predators Owl Rock Member, 33, 34, 35 Petrified Forest National Park Price River Formation, 183, 214 Oxyclaenus pugnax, 215, 216 (Arizona), 35, 36, 42–43 Price River Quarries, 146, 149, 158 Phillips, John, 2 Proboscidea, 247 Pachycephalosauria, 252 Phobosuchus, 6 Promioclaenus acotylus, 215, 216 Pacific Ocean, 32 phytosaurs, 25, 38, 60 Protoceratops, 152 Padian, K., 65 Phytosaurus, 38 prosauropods, 27, 40, 41, 63–64, Page Sandstone, 70 Placerias, 25, 39 67–68, 250 “paleochannels,” 166, 167 Planicoxa venenica, 156 Protosuchus, 60, 61 paleomagnetism, 10 plants: and aquatic ecosystem of Pseudosuchia, 24 Paleontological Resources Lake Dixie, 56; and Chinle psittacosaurs, 191 Preservation Act of 2009 (PRPA), Formation, 35–37; and extinctions Pteraichnus, 66–67, 73, 74 vii–viii, 239–40 of late Triassic, 46; increase of pterosaur(s), 61, 66–67, 73–74, 141, paleontology and paleontologists: in uppermost Cedar Mountain 177, 247 Index 291

Pterosauria, 247 Rocky Mountains, 212 and Ankylosauria, 111; and pubis: of ceratosaurs, 122; of rostrum, of Triceratops, 220 Scutellosaurus, 64–65 Ornithischia, 247, 248, 250, 251; of Rough Road Quarry, 146, 149 seabirds, and Mancos Sea, 175, 177 Tetanurae, 125 Ruby Ranch Member, 148, 158–69 seafloor spreading 10 Puertasaurus, 219 Russell, D. A., 19, 26, 98, 137, 227 sea level: and late Cretaceous, 167, Purgatoire River (Colorado), 85, 91 Rutiodon, 25, 38 233; and Mesozoic oceans, 8–9 Pycnodonte newberryi, 173 seasonality: of climate during St. George (town), 17, 53 Maastrichtian in central Utah, Quartzite, 147 St. George Dinosaur Discovery Site 215; of climate in Morrison Basin, Quetzalcoatylus, 6 (SGDS), 54–57, 60, 242 83–85 Saltosaurus, 249 sedimentary rocks, and Mesozoic radiometric dating, 16 Salt Wash Member, 14, 77, 78, 79–80, geology of Utah, 12–14 Raft River Range, 146 126 Seeley, H. G., 247 Rancho La Brea tar pits (California), sand sea, and fossils from Navajo Segi (Tsegi) Canyon (Arizona), 68 132 Sandstone, 66–69 Segisaurus, 68–69 “raptors”: and Dromaeosuridae 138, sandstones, 50, 170. See also Sego Sandstone, 183 152; and therizinosaurs, 151. See Aztec Sandstone; Entrada Seismosaurus, 92, 96–97, 249 also oviraptorosaurs Sandstone; Ferron Sandstone; Seitaad ruess, 67–68, 69 rauisuchians, 25–26 Navajo Sandstone; Poison Strip selenium, 172 red beds, of Chinle Formation, 35 Sandstone; Sego Sandstone; Semionotus kanadensis, 56 Redfleet Reservoir, 73 Sunnyside Sandstone; Wingate Sertich, J. J. W., 67 reproduction, and migrations of Sandstone Sevier Desert, 179 Morrison dinosaurs, 85 sanidine, 16 Sevier foreland basin, 180–83, 213 reptiles: and Chinle Formation, San Juan County, 86 Sevier Orogenic Belt, 82, 146, 147, 39; classification of, 247; San Pitch Mountains, 214 171, 178–80, 212, 213 development of during transition San Rafael Group, 70–74 sexual dimorphism: of Allosaurus, from Paleozoic to Mesozoic, San Rafael Swell, 50, 70, 144, 212, 128; of ceratopsians, 224; 24; of early Triassic, 24, 39; and 213, 214 of ceratosaurs, 122–23, extinctions in late Paleozoic, 4; Saurischia, 247, 248–50 124; and identification of and extinctions in late Triassic, Sauropelta, 154, 161–62 species of dinosaurs, 253; of 47. See also lizards; snakes; turtles Saurophaganax, 133 Parasaurolophus, 196 Reptilia, 246–47 sauropod(s): and Alamosaurus, 217, shale, 172. See also Arapien Shale; Revueltosaurus, 44 218; and dinosaurs of Morrison “black shale”; Mancos Shale; Rhamphinion, 61, 67 Formation, 86–105; Jurassic Mowry Shale; Tropic Shale rhynchosaurs, 26 as “Golden Age of,” 218; from sharks, 5, 174 Rhynosaurpoides, 41 Long Walk Quarry in Cedar Shay Canyon, 40, 41 Rice, G., 227 Mountain Formation, 159–60; Shinarump Conglomerate, 35 Richardoestesia, 164 and migrations in late Jurassic, Shinarump Member, 33, 34, 35 Rioarribasaurus. See Coelophysis 84, 85; and “sauropod hiatus” “shocked” mineral grains, and Riojasaurus, 250 in early Cretaceous, 218, 220; asteroid impacts, 11, 231 rivers: and climate of late and systematic bias in fossil Shuvosaurus, 43 Cretaceous, 167; and North Horn record, 21. See also Diplodocidae; Siberia, 170 Formation, 214; and Salt Wash prosauropods Sierra Nevada, 82 Member of Morrison Formation, Sauropodamorpha, 218, 248–50 silica, 19, 79 79; and sandstones of Kayenta Scaphites, 173. See also ammonites Simpson, E. L., 193 Formation, 53; and sedimentary S. warreni, 5 skeletal features: and definition deposits, 13; of Utah in early Scelidosaurus, 65–66, 248 of dinosaurs, 244–45; Cretaceous, 146–48. See also Schulte, P., 228, 229 plesiomorphic and apomorphic Colorado River Scutellosaurus, 47, 64–65, 66 types of, 25. See also feet; hands; Rock Point Formation, 35 scutes: and aetosaurs, 65–66; ilium; ischium; neck; neural 292 Index

spines; pelvis; pleurocoels; pubis; species, and classification of of Camarasaurus, 98–99; scutes; skulls; tail; vertebrae dinosaurs, 252–54. See also of Ceratosaurus, 124; of skin impressions: of Barosaurus, armor; ichnospecies diplodocid sauropods, 87, 91; 95–96; and fossil record in Utah, speed, and specialization of of hypsilophodontids, 114; 17; of hadrosaurs, 198–99; in Dryosaurus, 116 of Parasaurolophus, 197; of Neslen Formation of Mesaverde spikes, on tail of Stegosaurus, 107, Seismosaurus, 97; of Stegosaurus, Group, 187. See also camouflage; 108, 109. See also thumb spike 107, 108, 109 color Springdale Member, 58 Talos sampsoni, 203–4 skulls: of Allosaurus, 127– Stegosauria, 84, 105–10, 251 tar pits, as “predator traps,” 132 28; of Apatosaurus, 92, 93; Stegosaurus, 94, 105, 106–10 Tawa hallae, 43 of Camarasauridae, 97; S. armatus, 252 taxonomy: and bias in fossil of Camarasaurus, 98; of S. stenops, 110, 252 record, 21; of Ornithopoda, 155; Camptosaurus, 112; of Cedarpelta, S. ungulatus, 110 of theropods, 120–21. See also 161; of ceratopsians, 192, 194– Stenopterygius, 6 cladistics; classification 95, 222, 252; of Ceratosauria, Stokes, W. L., 31, 130, 131, 132, 134, 144 technology, and advances in 122, 123–24; of cetiosaurs, Stokesosaurus, 130 paleontology, 238 105; of Coelurosauria, 135, S. clevelandi, 134–35 Tecovosaurus, 44 136; of Deinosuchus, 206; of stomach contents, and fossil record, teeth: of Abydosaurus, 160; of diplodocid sauropods, 86, 18. See also gastroliths Alamosaurus, 217; of Allosaurus, 87, 88; of Dryosaurus, 115; Straight Cliffs Formation, 183, 185, 127; and bias in fossil record, of hypsilophodontids, 114; 190 21; of brachiosaurids, 102; of iguanodontids, 112, 114, Stump Formation, 73 of Camarasauridae, 97; of 157; of Ornithomimidae, 139; Stygmius, 6 Camarasaurus, 98, 100; of oviraptorosaurs, 203; of Styracosaurus, 192 of Camptosaurus, 112; of sauropods, 160; and skeletal subduction, and seafloor spreading, ceratopsians, 191, 221; of features of dinosaurs, 245, 246; of 11 ceratosaurs, 122, 123; of stegosaurids, 106; of Stegosaurus, suborders, and classification of cetiosaurs, 105; of Deinosuchus, 106; of Teratophoneus, 205, 206; dinosaurs, 246, 248 206; of diplodocid sauropods, of Tetanurae, 125; of Torosaurus, subsurface cavities, in Wahweap 86, 87, 88, 91; of Dryosaurus, 222; of Torvosaurus, 134; of Sandstone, 193 115; of herbivorous reptiles troodontids, 203. See also brain sulfurous gases, and volcanic from Chinle Formation, 44; case; cheek pockets; eyes; frills; eruptions, 11 of hypsilophodontids, 114– horns; teeth Sullivan, R. M., 175 15; of iguanodontids, 114, 155, “slickrock,” 50 Summerville Formation, 70, 72, 73 156, 157; of Marshosaurus, Slickrock Member, 72 Sundance Formation, 73 139; of Massospondylus, sloths, 178 Sunnyside Sandstone, 183 63–64; of Ornitholestes, 136; Smithsonian Institution, 216–17, 220 “sunset agate,” 79 of Parasaurolophus, 197; of Snake Range (Nevada), 70, 76 “superplumes,” of late Mesozoic, 11 stegosaurids, 106; of Stegosaurus, snake(s): classification of, 247; and Supersaurus, 96 106; of Stokesosaurus, 135; of Morrison Formation, 141. See also swimming tracks, of theropods, 57 Tetanurae, 125; of theropods, reptiles symmetrodontids, 141–42 165; of therizinosaurs, 151; social organization, and herding synapsids, and Paleozoic, 4 of Torvosaurus, 134; of behavior in Diplodocus, 88 synorogenic conglomerates, 181 Troodontidae, 140, 164; of South America: and origins of first Syringopora, 2 Tyrannosaurus, 225 dinosaurs, 26; and sauropods in systematic bias, in fossil record, 21 temporal fenestrae, 246 Maastrichtian age, 219–20 Tempskya (fern), 166 Southern San Rafael Swell, 146 tail: of Allosaurus, 128; of Tendaguru Formation (Tanzania), specialization: of Dryosaurus for Apatosaurus, 93–94; of 96, 124–25 speed, 116; of theropods for Barosaurus, 95; of brachiosaurids, Tenontosaurus, 163, 251 predation, 121 102; of Camarasauridae, 98; Teratophoneus curriei, 205–6 Index 293 terrestrial environments, adaptations 226, 252. See also Ceratopsia and and volcanoes in Mesozoic of dinosaurs to, 244 ceratopsians landscapes of, 15–16; early Tertiary period (Cenzoic), 210 T. horridus, 224 Cretaceous dinosaurs in, 150; Tetanurae, 121, 125–35, 248 T. prorsus, 224 and early Jurassic rock sequence, Tethys Sea, 6 triconodontids, 141–42 48–53; eastern as natural Tetrasauropus, 40, 41 tritylodonts, 58, 61, 69 museum of Mesozoic, 1–2; and Thaynes Formation, 28 Troodontidae, 140–41, 164, 203 evidence for early dinosaurs in theodonts, 26 Tropic Shale, 9, 13, 173, 174, 175, 182 Chinle Formation, 39–42; and therapsids, 26 Tullock Formation, 228 fauna of Kayenta Formation, therizinosaurs, 151 Turner, C. E., 80 61–66; geologic vistas from thermoregulation, and plates of Turonian age, 185 state highways of, 12, 24, 75–76, Stegosaurus, 107, 108 turtles: and Kaiparowits Formation, 172, 193; geology of in early theropod(s): classification of, 120– 207; and Morrison Formation, Triassic, 28–31; geology of in 21, 248; and digging behavior, 193; 141; and North Horn Formation, late Triassic, 31–32; institutions and fauna of Kayenta Formation, 215; of Triassic, 26. See also and organizations with active 61–62; and footprints from reptiles programs in paleontology, 241– Shay Canyon, 40; of Morrison Twin Creek Limestone, 70 42; K-T boundary in, 211–13, Formation, 121–41; Nothronychus Typothorax, 39 215; late Cretaceous dinosaurs and adaptation for plant-eating, Tyrannosauridae, 134–35, 205, 248 of southern, 188–209; late 178; and pneumatic pockets, 43; Tyrannosaurus, 135, 225–26, 243, 248 Jurassic landscapes of, 78–86; and predators of Kaiparowits and marine invasion of middle Formation, 201–7; and prehistoric Uinta Mountains, 212, 213 Jurassic, 69–70; Mesozoic monsters in popular culture, 120; Uintasaurus, 98 and rock record of, 12–14; and Ruby Ranch Member, 165; Ultrasaurus, 103, 249 Mussentuchit Member and and swimming tracks in Lake Uncompahgre Highland, 81–82 landscape of, 167; and Office of Dixie, 57 unconformity: between Dakota State Paleontologist, vii, 239– Theropoda, 120 Sandstone and Cedar Mountain 40, 242; and rocks of San Rafael thrust faults, 179 Formation, 170; in Chinle Group, 70–72; and search for thumb spike: of Camptosaurus, Formation during mid Triassic, fossils from Glen Canyon Group, 112, 113; of Iguanodon, 45; and K-T interval, 213; and San 60; and Sevier Orogeny, 178–80; 114; of iguanodontids and Rafael Group in middle Jurassic, surge of new discoveries about camptosaurids, 112 72; and Tidwell Member of dinosaurs in, vii–viii. See also Thyreophora, 64, 106, 110, 251 Morrison Formation, 79; at top of specific geographic locations and Tidwell Member, 14, 77, 78, 79, 158 Moenkopi Formation, 32; at top geologic formations Titanosauridae, 218–20, 249 of Morrison Formation, 143–44 Utahceratops gettyi, 193–94, 195, 208 Torosaurus, 222, 223, 224 University of California Museum of Utah Division of State Lands, 239 T. gladius, 222 Paleontology, 60 Utah Field House of Natural History, T. latus, 222 University of Oklahoma, 149 242 T. utahensis, 222, 224, 226 University of Utah, vii, 202, 225. See Utah Friends of Paleontology, viii, Torvosaurus, 121 also Utah Museum of Natural 239, 242 T. tanneri, 133–34 History Utah Geological Survey, vii, viii, 149, trace fossils, 17 uranium, and Morrison Formation, 189, 239 Triassic: extinctions in late, 46–48; 77 Utah Museum of Natural History, global geography and climate Utah: Allosaurus as state fossil vii, 67–68, 149, 189, 237, 241 of, 23; and origins of dinosaurs, of, 126, 127; Cedar Mountain Utahraptor ostrommaysi, 151, 152–53 23–27; and reptiles, 24; Utah Formation and conditions in Utah State Highways, 12, 24, 75–76, geology in early phase of, 28–31; central, 168–69; conditions 172, 193 Utah geology in late phase of, during early Cretaceous in east- Utah State University, vii, 242 31–32 central, 143–49; and dinosaur Uteodon, 113 Triceratops, 190–91, 220–22, 223, 224, fossil record, 16–22; dinosaurs 294 Index variation, range of within species geology of Mesozoic, 10–11; and Whitmore Point Member, 54 of dinosaurs, 253. See also sexual K-T boundary, 231, 233; and wildfires: and K-T event, 231; and dimorphism Mesocordilleran High, 76; and Triassic-Jurassic boundary, 48 Velociraptor, 139, 152 Triassic-Jurassic boundary, 48 Wingate Sandstone, 49, 51, 53, 57–58 Venenosaurus dicrocei, 158 volunteers, and paleontology, 239 Woodside Formation, 28 vertebrae, of ceratosaurs, 122. See also caudal vertebrae; cervical Wahweap Formation, 183, 190–93 Yellow Cat Member, 148, 150–58, 169 vertebrae; neck; tail Wasatch Mountains, 179 Yucatan Peninsula (Mexico), 231 Viviparus, 3 Wasatch Plateau, 214 volcanoes and volcanic activity: Waterpocket Fold, 1 Zanno, L. E., 151 and Carmel Formation, 71; Wealdon Marl (England), 158 Zion National Park, 37, 50 and Chinle Formation, 33, 35; Weishampel, D. B., 155, 196, 197 zircon crystals, in volcanic ash, 143 and dinosaurs in Utah during Welles, S. P., 125 Zofiabaatar pulcher, 142 Mesozoic, 15–16; and fission- Western Interior Seaway, 167, 170, Zuni Uplift, 81–82 track dating of ash, 143; and 175, 180–83, 207, 208, 211–12