The Triassic coelurosaurian dinosaur, Coelophysis bauri, described by Cope on the basis of fragmentary remains, has become abundantly documented by the materials excavated from the now famous Coelophysis quarry at Ghost Ranch, New Mexico. This little dinosaur, some six feet in length as an adult, is probably the oldest saurischian and embodies the characters of an ancestral theropod dinosaur. Although it stands at the base of the saurischian evolutionary tree, it is nonetheless a highly evolved reptile. It was a member of the Chinle fauna of Carnian-Norian age, but it did not occupy the dominant position in the fauna that the dinosaurs enjoyed in Jurassic and Cretaceous assemblages. The remarkable concentration of Coelophysis skeletons in the Ghost Ranch quarry raises intriguing questions concerning deposition, ecology, climate, dinosaurian life histories and continental relationships during late Triassic time.