Coelophysis

Coelophysis is a genus of coelophysid theropod dinosaurs that lived during the late Triassic, from about 215 to 201.4 million years ago, in what is now the southwestern United States. It was a small, slender, ground-dwelling bipedal carnivore, reaching up to 3 meters in length. As one of the earliest known dinosaur genera, it is also one of the most specimen-rich. The genus *Megapnosaurus* was once considered a species of *Coelophysis*, but that view has been challenged, and *Megapnosaurus* is now accepted as a valid genus. Scattered remains of similar animals have turned up in Late Triassic and Early Jurassic formations worldwide.

The type species, *C. bauri*, was first placed in the genus *Coelurus* by Edward Drinker Cope in 1887 and described by him in 1889. The names *Longosaurus* and *Rioarribasaurus* are synonyms of *Coelophysis*.

In April 1887, Cope described vertebrate remains from the Triassic of New Mexico as new species of *Coelurus*, covering nearly the whole skeleton except the skull and teeth. While *Coelurus* had been considered an uncertain reptile by Othniel Charles Marsh, Cope’s new material showed it was a dinosaur, likely close to *Megadactylus* (now *Anchisaurus*) from the Triassic of Massachusetts. Cope named two new species from his New Mexican collection: *Coelurus longicollis* (based on multiple vertebrae and a pelvis) and *Coelurus bauri* (named after Georg Baur, covering similar skeletal regions). In July 1887, he reclassified these into the German genus *Tanystrophaeus*, creating *Tanystrophaeus longicollis* and *Tanystrophaeus bauri*. He later added *Tanystrophaeus willistoni*, named after Samuel Wendell Williston, for a partial pelvis even smaller than the others. Realizing the vertebrae he thought matched *Tanystrophaeus* were not definitely caudal, Cope gave the species a new genus name in 1889: *Coelophysis*, from the Greek *koilos* (“hollow”) and *fysis* (“form”), with three species: *C. longicollis*, *C. bauri*, and *C. willistoni*.

All of Cope’s original material was collected by David Baldwin in 1881 from three sites in Rio Arriba County, New Mexico. The only surviving labels indicate the specimens came from below a gypsum layer at “Arroyo Seco” and “Gallina Canyon.” That gypsum layer is now known to be part of the Middle Jurassic Todilto Formation, which overlies the Chinle Formation near Ghost Ranch, where Arroyo Seco (Arroyo Canjilon) flows. Baldwin must have collected from a region around Ghost Ranch where the river cuts through the Chinle below the Todilto gypsum. In 1912, Williston and Ermine Cowles Case believed they found Baldwin’s collecting area and located surface fragments they assigned to *Coelophysis*.

Friedrich von Huene reviewed *Coelophysis* in 1906, following Cope’s species identifications and illustrating the material for the first time, including hand elements of *C. longicollis* and vertebrae of *C. bauri* that Cope had not described. Huene did not consider *Coelophysis* closely related to *Anchisaurus*, instead placing it in Coeluridae. In a 1915 review limited to Cope’s New Mexican collection, Huene sorted the specimens into three species by size—*C. longicollis* largest, *C. willistoni* smallest—and suggested more than three species might exist. He designated no type species and identified no specimen numbers, complicating later assignments. In 1986, Kevin Padian revisited the type material, identifying which specimens Cope and Huene had referred to each species, and noted some material in Cope’s collection that remained undescribed.

In the summer of 1946, Edwin H. Colbert began searching for Triassic fossils in Petrified Forest National Park, Arizona, for the American Museum of Natural History. The next year, he planned to stop at Ghost Ranch on the way, where many phytosaur skulls had been found. The 1947 field crew included Colbert, George Simpson, Bill Fish, George Whitaker, and Tom Ierardi. Simpson and Fish worked on Eocene mammals in northern New Mexico, while Colbert, Whitaker, and Ierardi headed to northern Arizona for Triassic reptiles. On June 21, they explored the Chinle Formation near Ghost Ranch and uncovered a complete phytosaur skull. The next day, Whitaker discovered some remains.