A review of the systematic position of the dinosauriform archosaur Eucoelophysis baldwini from the Upper Triassic of New Mexico, USA

EZCURRA, M. D.

Geodiversitas

Publications Scientifiques du Muséum national d?Histoire naturelle

Lugar: Paris; Año: 2006 vol. 28 p. 649 - 684

1280-9659

Eucoelophysis baldwini Sullivan & Lucas, 1999 is represented by several postcranialelements from the Petrified Forest Formation (Norian), New Mexico,USA. Eucoelophysis Sullivan & Lucas, 1999 was widely considered as a coelophysoiddinosaur by several authors, but the hindlimb anatomy of this genusclearly indicates that it belongs to neither of these groups. The following featuresexclude Eucoelophysis from Neotheropoda: absence of oblique ligamentgroove on caudal surface of femoral head, femoral medial epicondyle small andsmoothly rounded, absence of caudal cleft between medial part of the proximalend of the tibia and fibular condyles, cnemial crest low, and fibular crest absent.Moreover, Eucoelophysis lacks dinosaurian synapomorphic characters, but hasa plesiomorphic slightly inturned femoral head that prevents its assignmentto Dinosauria. Interestingly, the morphology of the femur of Eucoelophysis isextremely similar to that of the basal dinosauriform Silesaurus opolensis Dzik,2003 from the Late Triassic of Poland. In order to determine the phylogeneticposition of Eucoelophysis, a cladistic analysis was carried out, which depicts Eucoelophysisas a non-dinosaurian dinosauriform. Thus reinterpreted, Eucoelophysisconstitutes the youngest record of a non-dinosaurian dinosauriform, indicatingtheir survival into the Norian, being co-eval with early dinosaurs.