Coelophysis ( traditionally; or , as heard more commonly in recent decades) is an extinct genus of coelophysid theropod dinosaur that lived approximately 228 to 201.3 million years ago during the latter part of the Triassic Period from the Carnian and Rhaetian faunal stages in what is now the southwestern United States. Megapnosaurus was once considered a species within this genus, but this interpretation has been challenged since 2017 and the genus Megapnosaurus is now considered valid. Coelophysis was a small, slenderly-built, ground-dwelling, bipedal carnivore that could grow up to long. It is one of the earliest known dinosaur genera. Scattered material representing similar animals has been found worldwide in some Late Triassic and Early Jurassic formations. The type species C. bauri, originally given to the genus Coelurus by Edward Drinker Cope in 1887, was described by the latter in 1889. The names Longosaurus and Rioarribasaurus are synonymous with Coelophysis. Coelophysis is one of the most specimen-rich dinosaur genera. History of discovery The type species of Coelophysis was originally named as a species of Coelurus. Edward Drinker Cope first named Coelophysis in 1889 to name a new genus, outside of Coelurus and Tanystropheus, which C. bauri was previously classified in, for C. bauri, C. willistoni and C. longicollis. An amateur fossil collector working for Cope, David Baldwin, had found the first remains of the dinosaur in 1881 in the Chinle Formation in northwestern New Mexico. Early in 1887, Cope referred the specimens collected to two new species, C. bauri and C. longicollis of the genus Coelurus. Later in 1887 Cope reassigned the material to a yet another genus, Tanystropheus. Two years later, Cope corrected his classification after realizing differences in the vertebrae, and named Coelophysis, with C. bauri as the type species, which was named for Georg Baur, a comparative anatomist whose ideas were similar to Cope's. The name Coelophysis comes from the Greek words κοῖλος/koilos (meaning 'hollow') and φύσις/physis (meaning 'form'), together "hollow form", which is a reference to its hollow vertebrae. However, the first finds were too poorly preserved to give a complete picture of the new dinosaur. In 1947, a substantial 'graveyard' of Coelophysis fossils was found by George Whitaker, the assistant of Edwin H. Colbert, in New Mexico, at the Ghost Ranch, close to the original find. American Museum of Natural History paleontologist Edwin H. Colbert conducted a comprehensive study of all the fossils found up