New Mexico Geological Society Downloaded from: http://nmgs.nmt.edu/publications/guidebooks/25 The Triassic paleontology of Ghost Ranch Edwin H. Colbert, 1974, pp. 175-178 in: Ghost Ranch, Siemers, C. T.; Woodward, L. A.; Callender, J. F.; [eds.], New Mexico Geological Society 25th Annual Fall Field Conference Guidebook, 404 p. This is one of many related papers that were included in the 1974 NMGS Fall Field Conference Guidebook. Annual NMGS Fall Field Conference Guidebooks Every fall since 1950, the New Mexico Geological Society (NMGS) has held an annual Fall Field Conference that explores some region of New Mexico (or surrounding states). Always well attended, these conferences provide a guidebook to participants. Besides detailed road logs, the guidebooks contain many well written, edited, and peer-reviewed geoscience papers. These books have set the national standard for geologic guidebooks and are an essential geologic reference for anyone working in or around New Mexico. 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One printed copy of any materials from the NMGS website or our print and electronic publications may be made for individual use without our permission. Teachers and students may make unlimited copies for educational use. Any other use of these materials requires explicit permission. This page is intentionally left blank to maintain order of facing pages. New Mexico Geol. Soc. Guidebook, 25th Field Conf., Ghost Ranch (Central-Northern N.M.), 1974 175 THE TRIASSIC PALEONTOLOGY OF GHOST RANCH by EDWIN H. COLBERT* INTRODUCTION STRATIGRAPHIC RELATIONSHIPS Triassic fossils were scientifically recognized in northern The Triassic in northern New Mexico, especially as it is New Mexico just a century ago when Edward Drinker Cope, exposed at Ghost Ranch and along the Rio Chama to the west, the famous paleontologist and zoologist from Philadelphia, is composed of the Chinle Formation. The Chinle has been passed through this region in 1874 on a journey from Santa Fe subdivided into several members, as follows: to Tierra Amarilla. On this trip Cope picked up a few fossil Petrified Forest Member reptilian bones in the vicinity of Gallina, where Upper Triassic Chinle Poleo Sandstone Member sediments are exposed at the base of Cerro Blanco. In the Formation Salitral Shale Tongue hundred years since Cope's chance discovery various paleontol- Agua Zarca Sandstone Member ogists have collected and studied Triassic fossils from northern New Mexico, to reveal a tetrapod assemblage of true signifi- These sediments, with a total thickness of 700 to 800 feet, cance for students dedicated to the study of organic evolution are of continental origin. The Agua Zarca, up to 100 feet in and the succession of vertebrate faunas during Mesozoic time. thickness, consists of conglomeratic sandstones and siltstones. Much has been learned as a result of work during the past The Salitral, which also may be 100 feet thick, is a variegated century on the Triassic vertebrates of the Southwest in gen- shale with limestone concretions. The Poleo sandstone, a rel- eral, and of New Mexico in particular. Much remains to be atively thin member, no more than 60 feet in thickness, is learned. nonetheless very resistant and topographically prominent. Three areas in northern New Mexico have yielded Triassic Most of the thickness of the Chinle Formation in this region is fossils: namely the slopes at the base of Cerro Blanco (already composed of the Petrified Forest Member, consisting of color- mentioned) a hogback immediately to the west of Capulin ful red, brown and purple clays, siltstones and sandstones. Mesa, as well as around the Mesa; the badlands at Ghost These beds are made up, to a large degree, of intricately inter- Ranch, and particularly the basal portions of the colorful cliffs tonguing lenses. (See also O'Sullivan, this issue, for a discus- which rise in spectacular splendor behind the ranch; and sion of Triassic stratigraphy in the Ghost Ranch area.) exposures in the vicinity of Lamy, to the south of Santa Fe. Our interest is in the first two of the areas listed, and especial- THE FOSSILS ly in the sediments at Ghost Ranch. Although fossils are known from the Agua Zarca, Poleo and COLLECTORS IN THE TRIASSIC Petrified Forest members, it is only in the last of these hori- zons that there is comprehensive paleontological evidence Cope's preliminary discoveries of 1874 have been men- bearing upon the Late Triassic life of New Mexico. Fossil leaves tioned. In 1881 David Baldwin, a professional collector, and wood are locally common in the Agua Zarca, Poleo and explored the Triassic beds around Capulin Mesa and at Ghost Petrified Forest beds, with the ancient conifer, Araucarioxylon Ranch. At the time he was working for Cope (he had pre- being perhaps the most characteristic plant. This is the tree so viously collected for Othniel Charles Marsh, Cope's bitter abundantly preserved in the Petrified Forest of Arizona, the rival). And as a result of his efforts he obtained bones of a type region for the Petrified Forest Member. Araucarioxylon is small Triassic dinosaur, described by Cope as Coelophysis. related to the modern arancarias, so typical of the Southern Some 30 years later, in 1911, this region was explored Hemisphere. The Poleo has yielded cycadeoids such as jointly by Samuel Wendell Williston and Paul Miller of the Otozamites and Zamites, and the cordaitalean, Yuccites, repre- University of Chicago, Ermin C. Case of the University of sented by strap-like leaves some two feet in length. Michigan and Frederick von Huene of Tübingen University. However, the bulk of the fossils in the Chinle Formation are However, the party was more concerned with the Permian found in the Petrified Forest Member. Besides plants there are vertebrates, to be found in the area near Coyote, than with fossil unionids—fresh-water clams—and fishes, amphibians and Triassic fossils. reptiles. The vertebrates are of particular significance, and to In the nineteen thirties the Triassic beds at Ghost Ranch them we will now turn our attention. were worked extensively by Charles Camp and Samuel Welles and their assistants, from the University of California at THE CHINLE VERTEBRATES Berkeley. A fine series of phytosaurs was collected. During this time Llewellyn Price and Theodore White collected the The vertebrates of the Petrified Forest beds in northern armored thecodont reptile, Typothorax, for Harvard. New Mexico may be listed as follows. After the second world war E. H. Colbert and his associates Fishes—Ceratodus, a lungfish opened a large quarry at Ghost Ranch, and excavated numer- Amphibians—Metoposaurus, a large labyrinthodont ous articulated skeletons of the dinosaur, Coelophysis. This Reptiles—Typothorax, a large, armored thecodont quarry has been subsequently worked. Rutiodon, a large crocodile-like thecodont *Curator of Vertebrate Paleontology, The Museum of Northern Coelophysis, a saurischian dinosaur Arizona; Curator Emeritus, The American Museum of Natural History, New York; Professor Emeritus, Columbia University, New York. Other fishes and reptiles are known from the Chinle Forma- 1 76 COLBERT tion in Arizona and Utah and from the related Dockum beds respects representing the climax of reptilian evolution. The in Texas and the Newark series in eastern North America, thus ancestral archosaurs were the thecodonts, essentially confined broadening our knowledge of Late Triassic life in North to the Triassic period. From the thecodonts there arose the America. But our immediate concern is with the Upper two orders of dinosaurs, the Saurischia and Ornithischia, the Triassic vertebrates of northern New Mexico. flying reptiles or pterosaurs, and the crocodilians. The birds also had their origins from the thecodont reptiles, or perhaps from some of the dinosaurs. Fishes The archosaurs anatomically were and are advanced reptiles, The lungfish, Ceratodus, is represented by its very character- active and frequently aggressive. The skeleton generally shows istic tooth-plates, which look something like combs with adaptations for rapid and well-controlled movements; the skull radiating ridges. These tooth plates show that the Triassic lung- commonly is lightly constructed, but very strong. The fish Ceratodus was closely related to the modern Australian archosaurs were the rulers of Mesozoic continents, and the lungfish, Epiceratodus. The Australian lungfish lives in rivers surviving crocodilians may be considered as very successful and lakes in Queensland. When the water inhabited by these reptiles, giving way only in recent years to the