Db_abstract

Topotypic material of Coelophysis bauri (Cope) and the Coelophysis-Rioarribasaurus-Syntarsus problem

Discusses the fossils later named Eucoelophysis, arguing that they are likely from the same stratigraphic level and locality as the original type specimens of Coelophysis.

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Abstract

The recent discovery of specimens, comparable to the syntypic series of Coelophysis bauri in both preservation and diagnostic features, challenge the belief that the syntypes were collected by David Baldwin at the site of the famous Whitaker (Ghost Ranch) Quarry (Rock Point Formation: Chinle Group). Five separate sites in the underlying Petrified Forest Formation (Chinle Group) around Orphan Mesa, located approximately 3.2 kilometers south of the quarry, have yielded indeterminate ceratosaur fossils which are considered topotypic material of Coelophysis bauri. These sites are located at the head of the east fork of the Arroyo Seco drainage, which is geographically contiguous with the main branch of Arroyo Seco. It is therefore most likely that Baldwin's material came from this area and not the site of the quarry.


The undiagnostic nature of the syntypes (including the recently designated lectotype [AMNH 2772] and the neotype [AMNH 2724]) renders Coelophysis bauri a nomen dubium. The name is not available for the skeletons from the famous quarry which have been recently designated Rioarribasaurus colberti. A number of specimens from the Smithsonian block (C-3-82) suggests referral of some specimens to a Syntarsus-like dinosaur based on pelvis morphology and the presence of incipient paired longitudinal skull crests (which are also present in Early Jurassic Syntarsus kayentakatae from Arizona). Synonymy of Rioarribasaurus with Syntarsus is premature, and the possibility of two closely related taxa occurring in the Whitaker Quarry cannot be ruled out.