The Paleobiology of Coelophysis bauri (Cope) from the Upper Triassic (Apachean) Whitaker quarry, New Mexico, with detailed analysis

Here, we investigate the paleobiology of a single population of the Late Triassic dinosaur Coelophysisbauri from the Whitaker quarry at Ghost Ranch, New Mexico. The quarry, discovered by George Whitaker of the American Museum of Natural History in 1947, has produced about 30 large blocks of fossil material during two extended excavations by the American Museum during the late 1940’s and early 1950’s, and by the Carnegie Museum of Natural History during the 1980’s. At least a few hundred dinosaur skeletons are contained in these blocks. We have studied numerous quarry blocks at several institutions, but we concentrate on the block at the New Mexico Museum of Natural History (NMMNH).The Whitaker quarry lies near the center of the Upper Triassic Rock Point Formation of the Chinle Group in the Chama Basin of northern New Mexico, 30 m above the Upper Triassic Painted Desert Formation and 35 m below the Middle Jurassic Entrada Sandstone. Based on lithostratigraphy, tetrapod biostratigraphy and conchostracanbiostratigraphy the quarry is of Apachean (late Norian-Rhaetian) age.The NMMNH block was turned over and prepared from the bottom-up, thus revealing new details about thepaleoecology of the site. The quarry apparently preserves a single very large flock of Coelophysis bauri together with other larger and smaller animals that were washed into a topographic low containing a small pond, where they probably drowned and were buried by a sheet flood event from a nearby river. The quarry fauna comprises ostracodes and conchostracans from the pond deposit, large coelacanth and small redfieldiid fish, apparently from the river, and small through large reptiles represented by a sphenodontid and drepanosauromorphs (small), dinosaurs and other archosauromorphs (medium) and phytosaurs (large). We list and describe the quarry fauna, but the paleobiological analysis is confined to C. bauri.Our research generally agrees (and occasionally disagrees) with some previous workers, but also breaks considerable new ground. We find that Coelophysis bauri was a bipedal, carnivorous, theropod dinosaur that was a fast, agile runner and a diurnal, visually-oriented hunter. Based on skull and orbit morphology, and on a complete sclerotic ring present in one specimen, we assess the vision characteristics of C. bauri. Using bird and reptileoutgroups for comparison, particularly in the sclerotic ring morphology and the degree of binocular overlap of the visual fields, we convincingly demonstrate that the eyes of C. bauri ally with those of hawks and eagles, and probably had similar acuity, power of accommodation and depth perception. Thus, they were the eyes of a fast,agile hunter of small, fast-moving prey.Coelophysis grew quickly, in a more bird-like than reptile-like manner, and displayed numerous sexuallydimorphic characters, particularly in the skull and neck, and pelvis and sacrum. Although Coelophysis had many bird-like features, including its overall appearance, hollow bones and the oldest documented furcula (wishbone), its reproduction was probably more “reptilian” than bird-like. We demonstrate that Coelophysis probably invested about as much effort in reproduction as modern reptiles of similar size, producing a large number of relatively small eggs and providing at least some parental care. Yet at least on occasion it cannibalized its young. The Ghost Ranch flock of Coelophysis contained a great many more yearlings and juveniles than adults; about 20 yearlings for each of the largest adults. Sexual maturity probably onset between two and three years of age and the largest animals in the flock were seven years old, or older. The babies had a suite of characters that is common to many tetrapods.Compared to the adults, they had short snouts, large eyes, small hands, long legs and large pedes. The survivorship curve of Coelophysis indicates that juvenile mortality was very high, but if they survived for a few years, the chances for a long life were greatly increased