>. l1J >C\J :51'­ THE WANNAGAN CREEK QUARRY AND ITS PALEOCENE ~ ...... Vl o QJ ...... > o c IN BILLINGS COUNTY, NORTH DAKOTA ~­ 0""­ 0 0 .J::...... ­0 by '-0. Ow Za::: Bruce R. Erickson

REPORT OF INVESTIGATION NO. 72

NORTH DAKOTA GEOLOGICAL SURVEY

Don L. Halvorson, Stale Geolo~st

1982 ')(' WAN NAGAN CREEK QUARRY

NORTH DAKOTA

Loc~\ion and aerial view (inse\) of Wannagan Creek Quarry site looking east. THE WANNAGAN CREEK QUARRY AND ITS

REPTILIAN FAUN A (BULLION CREEK FORMATION,

PALEOCENE) IN BILLINGS COUNTY, NORTH DAKOTA

by

Bruce R. Erickson

I.. I REPORT OF INVESTIGATION NO. 72 r • NORTH DAKOTA GEOLOGICAL SURVEY

Don L. Halvorson, State Geologist

1982

Prinled by Associated Printers, Inc., Grand Forks, ND 58201 1982 CONTENTS

Page INTRODUCTION . . . 1 Historical Review 1 Acknowledgments 1 Geologic Setting . 2

QUARRY SIGNIFICANCE 3 Wannagan Creek Assemblage 3 Reptiles of Wannagan Creek 4 Taphonomy . 6 Paleoecology ...... 10 Evidence of Predation 11 Evidence of Nesting 14

SUMMARY .. 15

REFERENCES 16

ILLUSTRATrONS

Frontispiece Location and aerial view (inset) of Wannagan Creek Quarry site looking east

Figure Page 1. Lower jaw halves of a multituberculate, SMM P74. 24 .130 (top), and a primate, Pleisiadapis SMM P78 .14.61 (below) indicate the nature of the small mammal community of Wannagan Creek Quarry . 2

2. Articulated skeleton of Leidyosuchus formidabilis, SMM P74.24.6 length approx. 3.5 meters 4

3. Field sketch of alligator skeleton, SMM P72. 34.274 (posterior two-thirds) in situ showing extznsive scutellation of the caudal region . . . . . 6

4. Skull of fish-eating Champsosaurus, SMM P77. 33.24, showing the delicate cranial structures ...... 7

5. Section of map of Wannagan Creek Quarry illustrating the development of beach cusps and locations of associated vertebrate remains ...... 9

6. Diagrarrunatic reconstruction of Wannagan Creek Quarry site during the Paleocene ...... 10

7. The carapace (upper shell) of Protochelydra, SMM P75. 22.271 shows wounds inflicted by large crocodile teeth ...... 12

8. Shell differences in two snapping turtles, Protochelydra, SMM P75. 22.271 (Paleocene) and Chelydra (recent common snapper), SMM uncatalogued specimen ...... 13

9. A fragmented crocodile metatarsal, SMM P74.22.329 from the beach facies of Wannagan Creek Quarry shows the telltale marks of gnawing, presumably by small scavenging mammals . . .. 14 INTRODUCTION of aU the broken and weathered sur­ face materials for possible future Historical Review reference. Included in the hundreds of pieces recovered by this method were During the late summer of 1970 the many other crocodile bones and several author visited Paleocene exposures in more condyles as well as numerous western North Dakota to search for turtle and fish fragments, some small reported crocodile remains. Evidence of marrunal jaws, and a tiny bird bone. fossil crocodilians in the Dakota bad­ This survey clearly established the lands is not, in itself, cause for presence of a sizable group of animals surprise or even perhaps much in­ and perhaps a potentially important terest, as their osteoscutes (bony paleoecological site. plates) and vertebrae are among some Wannagan Creek Quarry was of the oldest known and most common opened the following year in 1971, and fossils of the West. The rather spec­ it has been intensively worked each tacular sample collection upon which subsequent year. During this period. the report was based, however, excavation has removed considerable deserved more than casual consider­ overburden resulting in a quarry ation; for among some 40 odd pieces of which presently encompasses some weathered bone, which had been 1,500 square meters (13,500 square collected the year before, were six feet). This effort has yielded a re­ occipital condyles of large adult croco­ markable fauna and flora in situ. It diles. The occipital condyle is a heavy, includes all classes of vertebrates, a solitary, bony structure at the back of modest number of invertebrates, and the skull that articulates with the first some interesting trace fossils in the vertebra of the backbone. Six of these form of burrows (Melchior and meant that at least six individual Erickson, 1979). crocodiles were represented--a rather Large amounts of matrix are high number for the limited sample. brought back from the quarry each This initial collection was made by year and subjected to a wet sieving Evelyn Sheldrup in 1969 while vaca­ treatment that separates the diminutive tioning in the area. It is not unusual bones and teeth from the matrix and in the annals of paleontology that retains them in fine mesh baskets. The significant discoveries have been made smaller jaw (fig. 1) is an example of by nonpaleontologists who were not in such a microfossil that probably would search of fossils. Too frequently, have gone undiscovered if it had not however, such discoveries go unre­ been collected in a sieve. corded. In the present case, Mrs. Because the great majority (over Sheldrup is to be commended for 70 percent) of the vertebrate animals bringing these materials to our atten­ found here are previously unknown to tion. science, the entire suite of specimens After a brief search, the exposure is collectively referred to as a "New from which the fossils were originally Fauna" and will henceforth be called collected was located and an examina­ the Wannagan Creek Fauna. tion of the site was begun. The large Each year additional new species number of bone fragments lying on the have been recovered. Until 1977 the surface of the ground at first sug­ rate of discovery of previously un­ gested a mere "bone hed"--a place identified species rose each year. where many bones had been deposited During that year alone nine new taxa and disassociated from one another by were documented. Considering the the action of water currents. Upon scope of the biota and the investi­ closer investigation it was revealed gating yet to be done, it is intended that, even though most of the visible that this discussion serve primarily as fragments were scattered at random, an introduction to the Wannagan Creek complete bones lying just beneath the Quarry community. surface were still intact and articulated with each other much as they had been Acknowledgments in life. This indicated that perhaps a complete skeleton might be found if a The writer is grateful to W. careful excavation were undertaken. Langston and J. Lang for helpful In order to begin a scientific suggestions on fossil crocodilians and excavation, a grid system was em­ discussions of behavior in living croco­ ployed to make a systematic collection dilians. Appreciation is extended to A. Figure 1. Lower jaw halves of a multituberculate, SMM P74.24.130 (top), and a primate, Plesiadallis SMM P78.14.61 (below) indicate the nature of the small mammal community of Wannagan Creek Quarry.

Cvancara and C. Carlson for important Badlands exposures here comprise contributions to the text and to R_ Late Paleocene clastics (weakly con­ Melchior for reading the manuscript. solidated sedimentary rocks) of the K. Sander provided figure 4 and Bullion Creek (=Tongue River; Clayton frontispiece and R. Spading provided et a1. , 1977) and Sentinel Butte all of the photographs. Much of the Formations of the Fort Union Group. research related to this report was These rock units were derived from supported by the Geneste M. Anderson sediments carried eastward by streams Paleontology Fund. flowing from the rising Rocky Moun­ tains, and consist of fluvial and Geologic Setting lacustrine sands, silts, clays, lignites, and limestones. The contact between Wannagan Creek Quarry (frontis­ the two formations is clearly marked piece) is located in the "upper breaks" by a prominent lignite bed (the HT of the Little Missouri River in Billings lignite; Royse, 1972) which is trace­ County, North Dakota. Runoff water in able for considerable distances. the area is delivered to the river by Wannagan Creek Quarry occupies a numerous tributaries that have deeply stratigraphic position some 20 meters eroded the bedrock and produced a (66 feet) below this major lignite bed badlands topography. One of the within the Bullion Creek Formation. largest streams is Wannagan Creek The quarry is on the summit of a from which the site takes its name. ridge that: is isolated on all sides but Steep vertical rock faces, slump blocks, the south. It is in a remnant of a local and earthflows further characterize the flood basin in which sediments accumu­ area. lated during a period of quiescence

2 and, therefore, form an uninterrupted QUARRY SIGNIFICANCE sequence. A lower gray silt containing many Wannagan Creek Assemblage pelecypods (clams) and a few gastro­ pods (snails) represents the initial Wannagan Creek Quarry has phase in the development of a back­ yielded a diverse biota with a verte­ swamp environment. This is overlain brate biota that would rival that of by a dark lignitic shale primarily made any extant crocodile-dominated habitat up of locally produced organic material. except for an absence of large mam­ It contains abundant crocodile and mals. Smaller vertebrates are repre­ turtle bones in addition to many deli­ sented by more than 30 species com­ cately preserved tree leaves. This bed prising a variety of fishes, amphibians, grades upward into a fine gray silt birds, and mammals. Their abundant that again contains many vertebrates, remains are found in the silt and clay but fewer plant fossils. Crocodiles are sediment and are recovered through still present at this horizon and sev­ laboratory processing of that material. eral varieties of fishes and plants There are several chelonians appear for the first time in the quarry (turtles) in this fauna. These are sequence. These new species and the represented by numerous individuals of fine-grained sediments suggest that a various age groups. Chelydrids (snap­ lacustrine (lake) environment followed ping turtles) are most abundant, the paludal (swamp) habitat. An un­ followed by emydids (pond tortoises) conformity (erosional surface) marks and a few trionychids (soft-shelled the top of this final bed. Above this forms). Protochelydra (Erickson, 1973) lies a massive layer of silty sand is the most common chelonian, making without fossils, which is interpreted as up about half of the specimens. It is a a crevasse splay (deposited during somewhat unusual "snapper" in having floods at breaks in the natural levee) a high-domed carapace (upper shell). from a nearby stream channel. Yet its cruciform plastron (lower shell) Within the quarry, the fossi/­ is of typical chelydrid design. The­ bearing beds have a dip that conforms emydids, at least two species, have to the morphology of the local flood low-silhouette shells and by contrast 0 basin. The dip is due south at 3-6 • A are scarce. Least conspicuous because thick sand facies along the north edge of their small size are the trionychids. of the quarry, where the dip is The largest number of young turtles slightest, has formed a series of belong to this group, including some discrete cusps that are interpreted as very small specimens and the site may beach features caused by gentle water have been a nesting area for turtles. movements. Minor intertonguing of Other reptiles, viz. , lizards, were sand and silt here demonstrates the generally small. In spite of the fact presence of a beach zone throughout that they are known from relatively the duration of the existence of the few specimens, two forms have been so swamp and lake phases. It further far identified, a varanid (Monitor) and demonstrates that only slight fluctu­ two species of Amphisbaenidae. Among ations of the shoreline took place the remaining associated aquatic verte­ during this time with perhaps some brates are a gigantic salamander, periodic flooding of subaerial surfaces; Piceoer~eton, and several primitive however, neither waves nor currents kinds 0 fishes including Amia (bowfin of significance are indicated. or dogfish) and Lepisosteus (garfish). As preserved, the total thickness The flora consists largely of leaf of these three fossil-producing beds is impressions and casts of fruiting only about 60 centimeters (2 feet). bodies, although much wood is also This sequence contains the total record present in the form of carbonized tree of the Wannagan Creek community . trunks and branches. There are 90 Beyond the limits of the quarry, documented species including some new correlations with surrounding strata taxa (Melchior, 1976, 1977). Abundant show dramatic changes in lithofacies plant remains indicate quiet water that (rock record) and different habitats was well shaded in places by large are implied. This is perhaps the prin­ overhanging trees and vines, and cipal explanation for the relative exposed to open sunlight in other paucity of vertebrate fossils outside places. A lush mat of emergent and the quarry deposits. floating aquatic plants is clearly

3 Figure 2. Articulated skeleton of Leidyosuchus formidabilis, SMM P74.24.6 length approximately 3.5 meters. Specimen collected from the lower level (swamp phase) ofWannagan Creek Quarry. defined by the fossil record. These Leidyosuchus formidabilis (Erickson, waters must have resembled some of 1976) with over 50 individuals ranging Florida's present-day everglades and in size from hatchlings 25 centimeters those of Chambri Lake in Papua, New in length, to large adults over 4 Guinea, where the floating vegetation meters long. Behavioral aspects of is so thick that man's fishing nets will these animals are revealed by this not penetrate. ontogenetic series and offer a most A few beetle elytra (wing cases) unusual glimpse into a Late Paleocene and two dragonfly wing imprints (as community. yet unnamed) are the principal re­ Leidyosuchus is a large eusuchian maining evidence of the insect life, crocodile (fig. 2) measuring over 3.5 which must have flourished here. meters in length. The skull possesses There were undoubtedly many other a rather long snout and has the gen­ 50ft-bodied forms that were not pre­ eral habitus of the American crocodile served. Rare forms that existed in Crocodylus acutus and the Nile croco­ limited numbers or for a very brief dile C. niloticus, both of which attain time may also have escaped detection. lengths comparable to that of the fossil There were surely other species as species. Outstanding features of the well whose flying or arboreal (tree­ mandibles are its long symphysial area climbing) habits allowed them to evade (where the halves of the lower jaw entrapment in the sediments that contact one another at midline) and the provide our collections. presence of two enlarged caninform These little known and seldom teeth near the front on each side of discovered forms add interesting the lower jaw. Lengthening of the details to the paleoecological inter­ symphysis is a structural modification pretation, but it is the plants and for strengthening the bite, and the larger vertebrates, namely the rep­ two enlarged teeth (3rd and 4th) were tiles, that contribute the greatest presumably a feeding adaptation as amount of evidence regarding the well. They are accommodated by a paleoenvironment of 58 million years wide, deep crocodyloid notch in the ago at the Wannagan Creek Quarry skull when the jaws are occluded. In site. The variety and durability of this feature there is a striking resem­ their bony parts affords the best blance to Diplocynodon of the Eocene record of the inhabitants of this an­ of North America (Mook, 1960) and cient community. Europe (Pomel, 1847). The postcranial osteology of this Reptiles of Wannagan Creek crocodile is of typical design; how­ ever, the front legs are unusually long The interest of the writer and the and suggest that it had better than abundance of the reptilian remains average capabilities for terrestrial leads to a more thorough examination locomotion. Most crocodilians have of these elements of the Wannagan much shorter forelegs and are bela­ Creek biota. Most outstanding of these bored arnbulators on solid ground; is the large eusuchian crocodile therefore, they are best suited to

4 sWimming or moving about in the water This small alligator bears a where much of their body weight is stronger resemblance to later alligators buoyed. than any of its contemporaries or A second noteworthy skeletal near-contemporaries of either Paleocene feature is the coat of heavy dermal or Eocene age. It is, therefore, osteoscutes (bony plates) that was hypothesized that it may represent one borne by this animal. These bony of the earliest of the lineage leading to plates, originally within the skin, are true alligators. It is characterized by individually broad, flat, and without its short broad skull and large bulbous crests. The larger ones evidently rear teeth that are designed for overlapped one another in life. Such crushing prey. extensive development of dermal armor A second specilnen .regarded as is usually a defensive adaptation conspecific (same species) is worthy of associated with terrestrial rather than mention in that it preserves the aquatic animals (Romer, 1956). The greater part of the postcranial skeleton obvious protection afforded by this (fig. 3). It was collected from nearby body armor, in any case, would seem deposits that are slightly older than to have been unjustified as there are those of the main quarry. Much of its no known Paleocene predators which osteodermal (bony armor) covering is would have been capable of "doing-in" preserved, and of special interest is such a large, formidable crocodile, the caudal (tail) section wherein except perhaps one of its own kind. osteoscutes apparently encircled the The heavy scutellation may have had entire structure forming a tail sheath some function other than protection, or as in Caiman (Romer. 1956). Many of it may simply have been a persisting the body and caudal osteoscutes bear primi tive character. In other struc­ low dorsal crests similar to those tures this crocodile appears to have possessed by the former specimen. The been amply equipped for an aquatic nuchal (nape of neck) and cervical existence. Unlike many of the smaller (neck) osteoscutes of the quarry vertebrates of Wannagan Creek Quarry, specimen show maximum development of whose numbers probably misrepresent these crests and a few of the forward their actual relative abundance in this ones have sharp, blade-like crests. A community because of their suscepti­ few other isolated osteoscutes were bility to transport (Korth, 1979), the found within the main quarry indi­ record of the large crocodile is judged cating the presence of additional to be indicative of the population size. individuals. Some studies (Cott, 1961; Webb, Another important reptilian element 1977) have looked at size to sex rela­ of this fauna is the longirostrine tionships of crocodile communities. (long-nosed) Champsosaurus. Together They show no obvious sexual dimor­ with the larger crocodile and the phism of contemporary forms so it 1s smaller alligator, three basic snout not possible to determine the sex of designs are established, each, no the collected specimens. However, it is doubt, with its own special functional assumed that the largest skulls and purpose. In spite of its fairly large corresponding number of parts of the size (average length of about 3 meters) largest propodials (major limb bones) bones of this highly specialized fish­ belong to males. eating reptile are found in limited A single, nearly complete skeleton quantity within the main quarry, of a small species of alligator (esti­ whereas elsewhere it is abundantly mated length of 1.2 meters) accounts represented. The implication is its for the only other crocodilian species preference for waters not inhabited by so far known from the site. This form crocodilians, which may have preyed (as yet unnamed) is unique as it is upon it. Throughout its history, the earliest known association of alli­ Champsosaurus has maintained a con­ gator and crocodile. Early alligator­ stant association with crocodilians crocodile associations are known in but (Erickson, 1972). Its skull is superbly a few places (Berg, 1966; Krumbiegel, designed for capturing fishes (fig. 4). 1959), and most. associations that are With its long, narrow jaws, lined with suspected are based upon rather many small sharply pointed teeth, this tenuous stratigraphic correlations. predator adequately filled a role similar Therefore, this newly discovered to that which was later so successfully evidence of coexistence is of consider­ assumed by long-nosed garfishes as a able interest. subordinate predator existing with

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Figure 3. Field sketch of alligator skeleton, SMM P72.34.274 (posterior two-thirds) in situ showing extensive scutellation of the caudal region. Collected 100 yards north ofWannagan Creek Quarry at a slightly lower level. crocodiles. The skull is a complicated known from the quarry; however, structure, as well as fragile, due to research in progress by the writer its widely expanded cranial vault of suggests that Champsosaurus and thin bony bars and plates whose Simoedosaurus coexisted but each function is uncertain. Figure 4 illus­ occupied a very different niche. It is trates its unusual construction. further suspected that the larger There is a remote possibility that simoedosaur, even more so perhaps among the champsosaur remains, than the champsosaur J preferred an especially the numerous vertebral environment without large crocodiles centra, some few elements belong to because of the even greater likelihood another reptile, Simoedosaurus. This of being preyed upon by the large closely allied genus has been recently crocodile. discovered in North America (Russell and Baird, 1978). Although somewhat Taphonomy larger, its vertebrae, as well as some of its other bones, are remarkably The term "taphonomy" as proposed similar to those of Champsosaurus. The by Efremov (1940) is that division of resemblance has very likely contributed paleontology which treats the conver­ to its lack of recognition in the past. sion of living animals to fossils. A No evidence of a simoedosaur is yet number of assemblages have been

6 Figure 4. Skull of fl!h~ting Champsosaurus, SMM P77.33.24, showing the delicate cranial structures. Skull length S6 em. analyzed for their taphonomy. A com­ up still retain their lower jaws in mon aspect of many taphonomic studies articulation, as does one of the skulls is "mass mortality" ascribed to a "on edge. II The preference for an catastrophic event. The Wannagan "overturned" position clearly reflects Creek accumulation of crocodiles does the floating posture of a bloated not represent such a mass mortality. crocodile carcass, and the posture it is The remarkable size range of individ­ more likely to assume when settling to uals, including hatchlings, and the the bottom. It is further suspected vertical distribution of numerous that all of the present individuals, individuals throughout the sediments, which were floating carcasses at some suggest that a community of some point, first contacted the bottom stability existed for a substantial sediments in this position. Scavenging length of time. The causes of individ­ of these carcasses lying on the bottom, ual death seem to have been due to by other crocodiles, would have been a more normal events such as natural common event. During this process the attrition, and more traumatic causes, lower jaws could have been easily such as cannibalism, that were also separated and the heads overturned or operating to a considerable degree. partially overturned as is suggested in Twenty-seven complete skulls of at least 4 specimens. crocodiles distributed over much of the Individual integrity of most of the site show a definite preference of skeletons wherein postcranials, at least positioning with respect to dorso­ major portions thereof, remain proximal ventral orientation. Of these skulls, 7 to their respective skulls, attests to a are oriented with the dorsal surface disturbance, but not to transport. up, 16 with the palatal surface up, About half of the skulls (30 of which and 4 with a lateral side up, i. e., on are essentially complete) still contain edge. Three skulls having their palates most of their teeth within their respec­

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Figure 6. DiagrammatIc reconstruction of Wannagan Creek Quarry site during the Paleocene. left to right: Champsosaurus, alligator (yet unnamed, and Leidyosuchus, each occupying a special niche. Flora represented here: Cercidiphyllum (Katsura tree), palm, palmetto, Metasequoia (in distance), Azalia (water fern), and NelumbiuTTl (water lily).

waters. In rough water, the snout, sion the writer will consider, in detail, with its narial disc, must necessarily only some of those ecological factors be elevated at a rather high and that impinged directly upon the prin­ awkward angle to keep from "shipping cipal vertebrate, and to a lesser water. II In doing so the animal is set extent those that affected closely off balance and founders, causing the associated taxa. Some preliminary head to slip backward underwater behavioral reconstructions will also be (Cott, 1961). In a place of congrega­ hypothesized. tion such as at Wannagan Creek The two crocodilians and Quarry, it is improbable that either Champsosaurus that inhabited the strong currents or significant waves quarry site area exploited a paleo­ were anything but unusual conditions, ecosystem that embraced a wealth of occurring only perhaps during storms, potential prey species within a setting and it is far more likely that the of dense vegetation typical of the existing disarrangement of skeletal North American Paleocene (Brown, remains was primarily the result of 1962). Figure 6 depicts diagrammati­ direct disturbance by the large croco­ cally these three principal predators in diles themselves. their resp~ctive niches. A few of the more salient floral types that flour­ Paleoecology ished in the immediate area are also indicated. Whereas the efforts of the ecologist A bit of insight into the role of are directed at understanding the the small alJigatorine may be gained if interrelationships of organisms that one considers the peculiar niche it live together, the work of the paleo­ filled as a rather inconspicuous con­ ecologist is concerned with recon­ temporary of a large group of aggres­ structing the extinct environment sive crocodiles. Its general skull which associated organisms inhabited. structure and tooth form suggest an Complexities of the paleoenvironment omnivorous habit that may have can only be imagined, and this included any of the numerous small attempted assessment of a few relation­ vertebrates as well as invertebrates as ships emphasizes the great amount of prey species. The abundant vegetation, lengthy analysis that is still needed especially the emergent types growing for the reconstruction of the Wannagan in the shallows, would have prOVided Creek paleocommunity. In this discus­ suitable refuge and a productive

10 stalking territory. Its poor representa­ hangs the much smaller xiphiplastra tion would indicate a sociality quite (rear part of plastron) and is more different from the apparent gregarious easily "grabbed" by opposing jaws. habits of the large crocodile. Like Partial penetration of the bony cara­ other early alligators. this new form pace resulting from an unsuccessful inhabited a swampy realm that meant capture attempt was evidently a fre­ reduced visibility. Garrick and Lang quent occurrence as most of the shells (1977) discussed the need for vocal­ bearing wounds also show evidence of izing among extant alligators under subsequent healing. Similar injuries such conditions, and further suggested are frequently observed in living the possibility of vocal signaling in turtles that are habitually associated extinct species. If such intraspecific with crocodilians. communication became part of the basis Protochelydra remains appreciably for the remarkable adaptations and outnumber those of other turtles in ultimate survival of this special group this deposit. Its carapace is rather of crocodilians, it is possible that their highly domed for a snapping turtle early crocodile associations provided (fig. 8) but is otherwise characteristi­ the pressures. which. in turn. evoked cally chelydrid in form. Aside from such innovative behavior. Distribution any other adaptive advantage (either of the Alligatorinae by the Paleocene aquatic or terrestrial) that this feature and Eocene is nearly world-wide (Sill, may have bestowed upon its possessor, 1968) demonstrating their early suc­ its shape made it invulnerable to all cess. but the largest of jaws that might securely seize it. Presumably a capable Evidence of Predation predator in its own right, In his lengthy analysis of feeding Protochelydra successfully coexisted behavior of the Nile crocodile, Cott amongst a population of large croco­ (1961) observes that crocodilians diles. Although not present in large occupy no single niche. but many; numbers. Trionyx (soft-shelled turtle) therefore. they usually have a varied may also have been a predator upon plentiful food source available to them. young crocodilians. Flower (1933) This includes predation up to one-half notes the heavy toll they inflict upon mile from the water. It is possible that hatchling crocodiles today. the large Paleocene crocodile Scatological evidence shows that Leidyosuchus resembled the living form fishes were also part of the diet of in this respect. If its terrestrial Leidyosuchus. Among some 300 copro­ capabilities were as well-developed as lites (fossil feces) examined in this its limbs and feet indicate. its hunting regard, some 100 were rejected on size range could have exceeded this. Few and shape as possibly belonging to large terrestrial prey species were other species. perhaps Champsosaurus. available, however. and, unlike the Of those remaining. 21 were found to Nile crocodile's diet, which includes contain inclusions mostly of fragmented numerous ungulate (large-hoofed) ganoid scales. These are plentiful mammals, that of Leidyosuchus must enough to make the assumption that have been limited to aquatic forms and garfishes were relatively abundant and resembled that of the American croco­ were a habitual part of the diet. dile in its more piscivorous (fish­ Regulation of population size in the eating) habits. living Nile crocodile is related to The most conspicuous evidence predation or cannibalism rather than that demonstrates predation by this food supply (Cott, 1961). Cannibalism large crocodile is a suite of turtle is a normal practice for the Indo­ shellS in diiferent states of complete­ Australian species (Webb, 1977). ness, and representing several distinct unknown in some caiman. even under species. Most exhibit perforations and the most adverse conditions of seasonal surface scars in the posterior (rear) overcrowding (Lang, personal regions (fig. 7) . These anomalies can cornmun., 1979), and only suspected in be directly associated with the large others. From what can be discerned caninform teeth in the jaws of about the potential food source that Leidyosuchus. The carapace (upper was available. as well as the absence

shell), rather than the plastron (lower of any potential predator I cannibalism shell), is more severely scarred. This must be given serious consideration as is due presumably to the structure of a behavior for this fossil population the shell wherein the carapace over­ also.

11 Figure 7. The carapace (upper shell) of Protochelydra, SMM P75.22.271 shows wounds infiicted by large crocodile teeth. Scale 10 em.

Among the many separate skeletal individuals within this general size elements of Leidyosuchus that were range relocate themselves to avoid deposited along the shoreline I about a contact with larger animals. dozen or so belong to hatchlings. This Cannibalism is further indicated by occurrence indicates the possibility of the disassociation of postcraniaI skele­ nearby nesting sites. Very young tons. In looking at the distribution of crocodilian remains are virtually absent the remains of Leidyosuchus within the from the fossil record (Langston, limits of the site, it is apparent that 1978). Apart from the special condi­ the majority of skulls lack complete tions required for their preservation, postcranial skeletons. A general dis­ their absence in the can temporary articulation and scattering of bones is environment is well noted. This is the rule and orientation seems random. believed due to a wide variety of A total of some 50 individuals have accidents that befall them during the been so far recorded by skull count--a first year of life (Langston, 1978). number consisting of basicrania alone. Much predation upon the very young A total of only 705 vertebrae are may be due to cannibalism by larger accounted for, and 2930 osteoscutes animals inhabiting the same area. In have been recovered. This is obviously addition to hatchlings, the relative size much less skeletal material than that and length of other young individuals which was originally present. found within the deposits of Wannagan Little evidence exists of any water Creek Quarry agrees, in general, with current that could have acted upon the those of contemporary populations assemblage as a transporting agent to wherein animals of overall lengths carry bones either into the site or around 1 to 1.5 meters are absent. away from it. Carcass scavenging by From this it is hypothesized that crocodiles is established behavior. In

12 Figure 8. Shell differences in two snapping turtles, Protochelydra, SMM P75.22.271 (paleocene) and Chelydra (recent common snapper), SMM uncatalogued specimen. The high-domed shell of the former is suspected to have had survival advantage in its association with large crocodiles. Scale 10 ern.

the process, many of the bones of represented and possibly may have dead animals are ingested and thereby been "gnawers." In light of this, and removed from the system through the the arboreal habits suspected for some subsequent digestive processes. Bones of these forms in the overhanging that are too large to be ingested, such vegetation, it is likely that they were as skulls and mandibles are largely occasionally eaten by smaller crocodiles ignored and remain as part of the as well as alligators. Neill (1971) faunal record (Behrensmeyer, 1975). reports that food of the modern alliga­ This probably accounts for the dis­ tor, although diverse, should reflect parity of skull and skeletal material. the local abundance and availability of Pathological alterations of bones some particular prey organisms. among the adults of the population are Although there is no direct evidence of fairly common, consisting of fractures, their predation by the small alligator, punctures, various kinds of lesions, this rather rich fauna suggests that an and plastic deformations. All but the ample food source was available in latter condition were due largely to small mammals alone. traumatic, nonfatal causes, as most All living crocodiles possess gas­ show evidence of healing. These con­ troliths (stomach stones). Gastroliths, ditions are largely attributed to intra­ whether used for hydrostatic control specific encounters. (Cott, 1961) , or as an aid in diges­ Least obvious of potential prey tion, or both (Webb, 1977), are nor­ species are perhaps the diminutive mally present where crocodile assem­ mammals that existed in prodigious blages are found; however. none have numbers and many varieties. Although been found at this site. Cott (1961) none are thought to have been aquatic, notes that swamp crocodiles lag some­ some had a strong tendency toward what in gathering stones because of arboreal niches. In spite of the large bottom type, but do eventually acquire amount of small mammal remains that them. Remains from several deposits occur at this site, their relative num­ such as those from the Geiseltal con­ bers in life may have been somewhat tain "Magensteine" (Krumbiegel, 1959), fewer, as the effects of stream flow as do those from Grube Messel (per­ may concentrate these elements. sonal obser.). Even very young soli­ The occurrence of unabraded, and tary individuals contain them gnawed, crocodile bones (fig. 9) , (Langston, 1978). Asswning that however, clearly demonstrates the stomach stones were originally present presence of at least certain species of in this population, they either: (1) micromammals in the immediate area. were removed subsequent to deposition Two characteristic mammalian types of of the carcasses, or (2) are present the deposit are multituberculates and but unrecognized for what they are. primates (fig. 1). Both are fairly well Removal by transportation seems very

13 Figure 9. A fragmented crocodile metatarsal, SMM P74.22.329 from the beach facies of Wannagan Creek Quarry shows the telltale marks of gnawing, presumably by small scavenging mammals. unlikely. Dissolution is a possibility if relative durability of certain crocodile the objects selected, perforce from bones, three contemporary crocodile some convenient location away from the bones were placed together in a HC1 site, had the capability of performing solution (pH 1.5) and regularly agita­ and enduring, for a time, the func­ ted. After 10 weeks the vertebra and tions of stomach stones, only to break two large osteoscutes remained intact down upon the demise of the animal. and showed only moderate erosion and Yet this is highly unlikely, as some softening of their surfaces. It is not traces surely would remain in one of unreasonable then to asswne that some the lithologies of the site. of the ingested bones may have been A more plausible explanation is the pressed into service as gastroliths. It utilization of osteoscutes and other is likely that such "stones" would not smaller bones, such as vertebral be as durable as those more conunonly centra, as gastroliths, in lieu of more utilized (e. g. , pebbles) and would suitable objects. Cott (1961) notes that need occasional replenishing. where crocodiles exist in nUmbers, they die in numbers, leaving their Evidence of Nesting rotting carcasses as carrion, and also A nesting site is suggested by the leaving nwnerous scutes and other existence of diminutive crDcodile bDnes bones to be ingested as gastroliths. It (Erickson, 1976) which fall within the has been suggested that the relatively size range that would be expected in low counts of vertebrae and osteo­ hatchlings of an animal comparable in scutes reflect the cannibalistic be­ size to the American and Nile croco­ havior of this crocodile- diles. Korth (1979) has shown the In an attempt to determine the susceptibility Df very small bones to

14 transport, and the unreliability of SUMMARY their presence as an indication of the faunal composition. Nevertheless, the The Wannagan Creek Quarry site environmental setting would favor them represents a unique look at a prolific as an indigenous segment of the pre­ fossil-bearing strata of Paleocene age. sent fauna. The attempted partial It is a remarkable site in the broad reconstruction of the paleoenvironment spectrum of species which have been of Wannagan Creek Quarry (fig. 6) preserved there, some of which are incorporates salient features derived similar to younger fossils, and a few from the evidence at hand, and that that are closely related to living kin. established by Cott (1961), as being Since Paleocene strata have had rather best suited for living crocodiles as limited study, this site has produced nesting habitats. many new species and further exca­ Firstly, a persistent beach zone vations will likely add to the list. As documents a rather stable condition of the end of 1980, 7 new species have with only minor fluctuations of the been described and at least an addi­ water's edge during the time which the tional 18 new taxa are believed to be Wannagan Creek fauna inhabited the present among all of the groups. flood basin. Mild abrasion is expressed Reptiles account for the majority of by some bones occurring within the the fossilized vertebrate remains. They beach zone; therefore, it is likely that also include the only complete skele­ at times the beach was awash. A short tons from the site. So far they are distance inland, however. the sand represented by two crocodilian taxa, must have stood high above the five chelonians, one champsosaurid. at water's surface as here it is over a least two species of lizard, and one meter thick and contains animal bur­ possible snake. Among the mammals, rows that are interpreted as those of multituberculates. insectivores, pri­ decapods (crayfish). This would have mates, and condylarths are repre­ been seemingly appropriate ground for sented by dozens of mandibles, soli­ nesting. tary limb and girdle bones, and many Nothing yet can be stated about isolated teeth. Dakotornis (Erickson, the location or type of nest that may 1975) is one of at least three different have been utilized. It is presumed that species of birds. Several amphibians a "nest" as described by Greer (1971) and fishes are present but only an was probably required for incubation estimate of about 10 different types of the eggs. Whether this was a mound can be made from their incomplete of sand or vegetation, or a simple pi t record. in the sand, is pure conjecture. The invertebrate fauna as yet is Secondly, the beach was situated largely unstudied; however. current with access to a fairly large body of laboratory preparation of quarry deeper water, thereby explaining the matrix indicates the presence of a presence of numerous, large (estimated variety of insects and mollusks. lengths up to 1.5 meters) fishes. In addition to the expanded know­ Finally, a forest canopy of large ledge of the Paleocene biota that this trees including magnolia, walnut, site has provided, it offers a detailed cypress, and the prevalent look at a paleocommunity. Comparisons CercidiphyHum (katsura tree) over­ of the fossil record at Wannagan Creek hung the beach and various shrubs and contemporary crocodile communities and vines formed a dense understory prOVides a means of reconstructing the (Melchior, personal commun.. 1980). climate and depositional setting in This vegetation provided the shade western North Dakota when the Iignite­ that is invariably associated with the bearing strata of the Fort Union Group nesting sites of contemporary croco­ (Paleocene) were being deposited. diles.

IS REFERENCES Proceedings Zoological Society London, p. 735-851. Behrensmeyer. A. K. , 1975. The Garrick, L. D., and Lang. J. W., taphonomy and paleoecDlogy Df 1977, Social signals and behaviors Plio-Pleistocene vertebrate assem­ of adult alligators and crocodiles: blages east Df Lake Rudolf, Kenya: American Zoologist, v. 17, p. Bulletin Museum Comparative 225-239. Zoology 146 (0), p. 473-578. Greer. A. E., Jr., 1971, Crocodilian Berg. D. E. , 1966, Die Krokodile, nesting habits and evolution: insbesondere Asiatosuchus und aff. Fauna 2, p. 20-28. Sebecus? , aus dem Eozan von Korth, W. W., 1979, Taphonomy of Messel bei DarmstadtlHessen: Abh. microvertebrate fossil assemblages; hess. L. - Amt. BodenfDrsch. 52, Annual Carnegie Museum Natural 105 p. History 48, p. 235-285. BrDwn, R. W., 1962, A PaleDcene flDra Krumbiegel, G., 1959, Die Tertiare Df the RDcky Mountains and Great pflanzen und tierwelt der Plains: U. S . GeDlogical Survey Braunkohle des Geiseltales: Die ProfessiDnal Paper 37S, 119 p. neue brehm bucherei, ClaytDn, L., CarlsDn, C. G., Moore, Whittenberg Lutherstadt, 156 p. W. L., GrDenewold, G., Holland, Langston. W., Jr., 1978, A yearling F. D., Jr., and Moran, S. R., crocodilian from the Middle Eocene 1977, The Slope (PaleDcene) and Green River Formation of Colorado: Bullion Creek (Paleocene) Forma­ Journal of Paleontology, v. 52, p. tions Df North Dakota: NDrth 122-125. Dakota Geological Survey Report of Melchior. R. C. , 1976, oreo~anax Investigation S9, 14 p. dakotensis, a new species 0 the Cott, H. B., 1961, Scientific results of Araliaceae from the Paleocene of an inquiry into the eCDIDgy and North Dakota: Scientific Publication economic status of the Nile croco­ of the Science Museum of dile (Crocodylus niloticus) in Minnesota, 3 (3), B p. Uganda and Northern RhDdesia: Melchior, R. C., 1977, On the occur­ Zoology Society London Transac­ rence of Minerisporites mirabilis in tions 29: p. 211-357. situ: Scientific Pubhcation of tfie Efremov, r. A., 1940, Taphonomy: a science Museum of Minnesota 3 new branch of paleoecology: (4). 16 p. Panamanian Geologist. v. 74, p. Melchior, R. C., and Erickson, B. R., 81-93. 1979, Paleontological notes on the Erickson, B. R., 1972, The lepido­ Wannagan Creek Quarry site saurian reptile Champsosaurus in (Paleocene-North Dakota) Ichno­ North America: Scientific Museum fossils I: Scientific Publication of of Minnesota Monograph 1, paleon­ the Science Museum of Minnesota 4 tology. 91 p. (4), 16 p. EricksDn, B. R., 1973, A new chely­ Mook, C. C. , 1960, Diplocynodon drid turtle Protochelydra zangerli remains from the Bridger Beds of from the Late Paleocene of North Wyoming: American Museum Natural Dakota: Scientific publication of History, Novit. 2007: p. 1-4. the Science Museum of Minnesota, Neill, W. T., 1971, The last of the v. 2, no. 2, 16 p. ruling reptiles: alligators, croco­ EricksDn, B. R. , 1975, Dakotornis diles and their kin: Columbia cooperi, a new Paleocene bird frDm University Press, New York and North Dakota. Scientific publication London: 486 p. of the Science Museum of Minnesota, Pamel, A., 1847. Note sur les animaux 3 (1), 7 p. fossiles decouverts dans les Erickson, B. R., 1976, Osteology of department de l'Allier: Bulletin the early eusuchian crocodile Societe Geologie France, Ser. 2, 4, Leidyosuchus formidabilis, sp. p. 378-385. nov. : Scientific Museum of Romer, A. S.. 1956, Osteology of the Minnesota Monograph 2. paleon­ reptiles: University of Chicago tology. 61 p. Press: 427 p. Flower, S. S., 1933, Notes on the Royse, C. F., Jr., 1972, The Tongue recent reptiles and amphibians of River and Sentinel Butte Forma­ Egypt, w1th a list of the species tions (Paleocene) of western North recorded from that kingdom: Dakota: A review: North Dakota

16 Geological Survey Miscellaneous Sill, W. D., 1968, The zoogeography Series 50, F. T. C. Ting, Editor, of the crocodilia: Copeia 1: 76-88. p. 31-42. Webb, G. J. W., 1977, The natural Russell - Signogeneau D. et D. Baird. history of Crocodylus porosus, in 197B, Presence du Genre Australian animals and their envi­ Simoedosauris (Reptilia, Choristo­ ronments: Shakespeare Head Press, dera) En Emerique Du Nord: Sydney, p. 285-312. Geobios No. 11: 251-255.

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