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Vertebrate Fauna of the Dockum Group, Triassic, Eastern New Mexico and West Texas Joseph P

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Vertebrate Fauna of the Dockum Group, Triassic, Eastern New Mexico and West Texas Joseph P New Mexico Geological Society Downloaded from: http://nmgs.nmt.edu/publications/guidebooks/23 Vertebrate fauna of the Dockum Group, Triassic, eastern New Mexico and West Texas Joseph P. Gregory, 1972, pp. 120-123 in: East-Central New Mexico, Kelley, V. C.; Trauger, F. D.; [eds.], New Mexico Geological Society 23rd Annual Fall Field Conference Guidebook, 236 p. This is one of many related papers that were included in the 1972 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. Free Downloads NMGS has decided to make peer-reviewed papers from our Fall Field Conference guidebooks available for free download. Non-members will have access to guidebook papers two years after publication. Members have access to all papers. This is in keeping with our mission of promoting interest, research, and cooperation regarding geology in New Mexico. However, guidebook sales represent a significant proportion of our operating budget. Therefore, only research papers are available for download. Road logs, mini-papers, maps, stratigraphic charts, and other selected content are available only in the printed guidebooks. Copyright Information Publications of the New Mexico Geological Society, printed and electronic, are protected by the copyright laws of the United States. No material from the NMGS website, or printed and electronic publications, may be reprinted or redistributed without NMGS permission. Contact us for permission to reprint portions of any of our publications. 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. VERTEBRATE FAUNAS OF THE DOCKUM GROUP, TRIASSIC, EASTERN NEW MEXICO AND WEST TEXAS by JOSEPH T. GREGORY Department of Paleontology University of California Berkeley, California DISCOVERY AND COLLECTION Robert Abercrombie of Norton, Quay County, New Mexico, OF TRIASSIC VERTEBRATE FOSSILS collected in this area for many years, sending specimens to Case and other paleontologists. He discovered the extensive Red beds along the Canadian River valley containing reptile trackways in the Redonda Formation on Mesa petrified logs were first described in 1853 by Jules Marcou Redonda. In 1947 J. T. Gregory began collecting in the who regarded them as Triassic in age. Bones of large reptiles Tucumcari area for Yale Peabody Museum, and later for the were discovered near Dockum, northwest of Spur, Dickens University of California. County, Texas, in 1890 by W. F. Cummins, and identified as R. V. Witter of Harvard University discovered the Triassic by E. D. Cope. Cope accompanied Cummins on a "Amphibian Graveyard" south of Lamy, Santa Fe County, in collecting trip along the east side of the Llano Estacado in 1936; collections were made here for Harvard by Witter and T. 1892 and secured additional Triassic vertebrates as well as E. White in 1938 and for the U.S. National Museum by David fossils from the late Tertiary and Pleistocene deposits. H. Dunkle, Franklin Pearce, and George Sternberg in 1947. The major portion of our knowledge of the Dockum verte- brates comes from the work of E. C. Case of the University of NATURE OF THE FAUNA Michigan who began describing fossils from Crosby County, Texas, in 1920, in part material found by G. D. Doughty of The Dockum fauna is typical of late Triassic continental Post, and William J. Eliot of Spur, Texas. Dr. Case returned to assemblages not only of the western United States, but of these localities repeatedly during the next 20 years and was most of the northern hemisphere. Many closely related or assisted in his fieldwork by William Buettner. In 1927 he col- identical genera of fishes, amphibians, and reptiles are known lected well-preserved reptiles near Otis Chalk, Howard County, from the Newark Group of the eastern United States, the Texas, and in 1930 he obtained an important concentration of Keuper Formation of Germany, the Maleri Formation of amphibians in northern Scurry County, Texas. The prolific site India, and recently discovered deposits in Morocco and the on Sierrita de la Cruz Creek northwest of Amarillo in Potter Sahara of Africa. Fragments of phytosaurs have been found in County, was discovered by Floyd V. Studer of Amarillo in Madagascar and China, and armored pseudosuchians are 1926; Case described material that he collected here in 1931; prominent in recently discovered late Triassic deposits of extensive collections were made around 1940 by the Pan- Argentina. handle-Plains Museum at Canyon, Texas. Dinosaurs are represented by infrequent and incomplete Further collections in the Otis Chalk region were made by J. fragments of at least two types; the slender, bipedal, predatory W. Stovall for the University of Oklahoma in 1931, and by Coelophysis, and the more probably quadrupedal prosauropod Grayson Meade for the University of Texas Bureau of Eco- Poposaurus, presumably an omnivore or even an herbivore. nomic Geology in 193901940. An important fish bed not far Pseudosuchians or "false crocodiles" were short-headed from the reptile quarries in Howard County, was collected by animals of crocodile-like proportions, protected by rings of Bobb Schaeffer for the American Museum of Natural History bony armor plates from which short spikes projected. In in 1954 and 1963. Another locality near Camp Springs in Desmatosuchus a pair of these spikes was enlarged into long Scurry County was found in 1937 (Langston, 1949). The Uni- curved horns above the shoulders. Their dentition was feeble, versity of Texas (Works Progress Administration) parties also and conjectures as to their food range from plants to carrion. collected from a site in southern Borden County, Texas, about Phytosaurs are by far the most abundant of the reptiles. 1940 and made additional collections from the well-known They were of the size and proportions of large crocodiles and Crosby County localities, some of which have also been probably of similar, mainly aquatic, habits. Paleorhinus and worked by Earl Green for Texas Technological College in Lub- Angistorhinus resembled the gavials of India in their very bock. slender jaws, and probably fed chiefly on fishes. The more In New Mexico, M. G. Mehl collected near Fort Wingate, massive Nicrosaurus (= Phytosaurus) could have preyed on McKinley County, in 1916, and in 1919 he described a larger land reptiles which ventured near the water, and on the phytosaur skull from near Santa Rosa, Guadalupe County. A large labyrinthodont amphibians of the streams and ponds. party from the University of Oklahoma under J. W. Stovall Rutiodon was intermediate in skull proportions but probably obtained a phytosaur from the Sloan Canyon Formation in the replaced Puleorhinus as a fish-eater in later Dockum time. Cimarron River valley, Union County, 1939. Fossil trackways Trilophosaurus had the proportions of a lizard, about 10 from the same beds at nearby localities have been described by feet long, with a short, deep head. Its jaws held a series of Baird (1964). Case and T. E. White prospected exposures chisel-like teeth, and terminated in a toothless, turtle-like south of San Jon and around Tucumcari in the early 1930s. beak. Apparently it chopped or tenderized its food before 120 swallowing it, but whether it fed on plants or insects has not BIOSTRATIGRAPHY been determined. Its remains are known only from Howard The implications of vertebrate fossils for correlation of and Crosby Counties, Texas, but closely similar forms have Triassic continental deposits of North America with those of been found in England. Europe have been summarized by Colbert and Gregory (1957, Metoposaurs are the last survivors of the labyrinthodont p. 1456-1457). The position of the Triassic-Jurassic boundary amphibians which were the dominant animals of the Carbon- in the Colorado Plateau is disputed currently (Welles, 1970, p. iferous coal swamps. Buettneria (also called Eupelor) had a 989; Galton, 1971, p. 781), but the beds in question lie above flat, wide body with disproportionately small legs and an ex- equivalents of the Dockum, whose faunas correspond in age to tremely large, flattened, wide head. These big amphibians, the middle Keuper of Germany. whose skulls may reach a meter in length, probably lay on the Detailed correlations within the Dockum are hindered by bottoms of shallow ponds or sluggish streams and engulfed incomplete knowledge of the assemblages from many local- fishes by suddenly opening their cavernous mouths. Their re- ities, and by nomenclatorial problems which obscure state- mains share top place in abundance with phytosaurs. ments about such relationships as are understood. At least Anaschisma is a related genus; Latiscopus a much smaller three distinct faunal zones may be recognized on the basis of labyrinthodont. evolutionary changes in the skulls
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