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New dinosauriform paper



Ezcurra, M. D., 2006.  A review of the systematic position of the
dinosauriform archosaur Eucoelophysis baldwini Sullivan & Lucas, 1999 from
the Upper Triassic of New Mexico, USA. Geodiversitas 28(4):649-684.

Abstract
Eucoelophysis baldwini Sullivan & Lucas, 1999 is represented by several
postcranial elements from the Petrified Forest Formation (Norian), New
Mexico, USA. Eucoelophysis Sullivan & Lucas, 1999 was widely considered as
a coelophysoid dinosaur by several authors, but the hindlimb anatomy of
this genus
clearly indicates that it belongs to neither of these groups. The following
features exclude Eucoelophysis from Neotheropoda: absence of oblique
ligament
groove on caudal surface of femoral head, femoral medial epicondyle small
and smoothly rounded, absence of caudal cleft between medial part of the
proximal end of the tibia and fibular condyles, cnemial crest low, and
fibular crest absent. Moreover, Eucoelophysis lacks dinosaurian
synapomorphic characters, but has a plesiomorphic slightly inturned femoral
head that prevents its assignment to Dinosauria. Interestingly, the
morphology of the femur of Eucoelophysis is extremely similar to that of
the basal dinosauriform Silesaurus opolensis Dzik, 2003 from the Late
Triassic of Poland. In order to determine the phylogenetic position of
Eucoelophysis, a cladistic analysis was carried out, which depicts
Eucoelophysis as a non-dinosaurian dinosauriform. Thus reinterpreted,
Eucoelophysis constitutes the youngest record of a non-dinosaurian
dinosauriform, indicating their survival into the Norian, being co-eval
with early dinosaurs.

An interesting paper that independently comes to the same conclusions as
Nesbitt et al. (2005), Parker et al. (2006), and Nesbitt et al. (in press)
in finding that Eucoelophysis is outside of Dinosauria.  This is important
because it demonstrates the presence of dinosauriforms in the Norian of
North America where they are contemporaneous with basal saurischians (e.
g., Chindesaurus) and theropods (Coelophysis).  The similarities with
Silesaurus are discussed.  A parsimony analysis supports the placement of
Eucoelophysis outside of Dinosauria.  Also of interest in this analysis is
the positioning of Eoraptor as the basal-most theropod and Herrerasaurus
and Staurikosaurus as a clade of basal saurischians.  This placement for
Eoraptor differs from the recent findings of Langer and Benton (2006) and
Rauhut (2003), where Eoraptor is outside of Theropoda.  The new topology is
also of interest as Ezcurra and Novas (2006) had earlier found Eoraptor and
Herrerasaurus to be basal theropods and thus more closely related.


References:

Ezcurra,  N.  D., and F. E. Novas, 2006.  Phylogenetic relationships of the
Triassic   theropod  Zupaysaurus  rougieri  from  NWArgentina.   Historical
Biology iFirst article DOI: 10.1080/08912960600845791

Langer,  M.  C.,  and Benton, M. J., 2006.  Early Dinosaurs: a phylogenetic
study: Journal of Systematic Paleontology 4(4):309-358.

Nesbitt, S. N., Irmis, R. B., and W. G. Parker, 2005.  Critical review of
the Late Triassic dinosaur record, part 3: Saurischians of North America.
Society of Vertebrate Paleontology 25(3):96A.

Nesbitt, S. J., Irmis, R. B., and W. G. Parker, in press.  A critical
reevaluation of the Late Triassic dinosaur taxa of North America.  Journal
of Systematic Palaeontology.

Parker, W. G., Irmis, R. B., and S. J. Nesbitt, 2006.  Review of the Late
Triassic dinosaur record from Petrified Forest National Park, Arizona.
Museum of Northern Arizona Bulletin 62:160-161.

Rauhut, O. W. M., 2003.  The interelationships and evolution of basal
theropod dinosaurs.  Special Papers in Palaeontology 69:1-213.


************************************************************************
Bill Parker
Vertebrate Paleontologist
Division of Resource Management
Petrified Forest National Park
P.O. Box 2217
1 Park Road
Petrified Forest, AZ 86028
(928) 524-6228 x262