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Eucoelophysis baldwini, a new theropod dinosaur from the Upper Triassic of New Mexico, and the status of the original types of Coelophysis

Describes the new dinosaur Eucoelophysis and argues that at least some of the original type specimens of Coelophysis may belong to this dinosaur.

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Abstract

Eucoelophysis baldwini is a new genus and species of theropod dinosaur from the Upper Triassic Petrified Forest Formation of the Chinle Group in north-central New Mexico. Eucoelophysis baldwini is diagnosed by the autapomorphous structure of its pubis (presence of ischio-acetabular groove), and femur, which has a sulcus in its proximal surface. It differs from Coelophysis bauri and Syntarsus rhodesiensis in lacking a well-developed posterior femoral notch below the femoral head. It is further distinguished from Coelophysis bauri in having a tibia that has a distinct appressed surface along the distal two-thirds of the bone and lacks a fibular crest. The original syntypes of Coelophysis longicollis (Cope, 1887a) include a pubis with autapomorphies of Eucoelophysis baldwini and can be assigned to that taxon. Many of the other syntypes of C. longicollis, C. bauri and C. willistoni probably also belong to E. baldwini, but this cannot be demonstrated with certainty. The type horizon of E. baldwini is in the upper part of the Petrified Forest Formation, about 45 m stratigraphically below the locality of the neotype of Coelophysis bauri, the Whitaker (Ghost Ranch) quarry, which is in the Rock Point Formation.