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Lepidus, new coelophysoid neotheropod from Upper Triassic of North America
A new online paper:
Sterling J. Nesbitt and Martín D. Ezcurra (2015)
The early fossil record of dinosaurs in North America: A new
neotheropod from the base of the Upper Triassic Dockum Group of Texas.
Acta Palaeontologica Polonica (in press)
The dinosaur record from the stratigraphically-lowest portions of
Upper Triassic deposits of western North America is poor and only
consists of a handful of fragmentary hind limb elements. Here we
present an articulated segment of the ankle region of a dinosaur that
consists of the distal ends of the tibia and fibula and a complete
astragalocalcaneum. Additionally, we suggest that an isolated femur
and maxilla from the same locality may belong to the same taxon. Using
the most comprehensive analysis of early theropod relationships
currently available, we determined that the new specimen pertains to a
coelophysoid neotheropod (i.e., more closely related to Coelophysis
bauri than to Allosaurus fragilis). The stratigraphic position of the
locality where the new specimen was discovered is equivalent to the
famous Otis Chalk localities and this set of localities likely
predates the rest of the Dockum Group and possibly the entirety of the
fossiliferous portion of the Chinle Formation on the Colorado Plateau.
Therefore, the new specimen represents one of the oldest neotheropods.
Accordingly, neotheropods were present at or just after the onset of
both the Chinle Formation and Dockum Group deposits.