New materials of an ornithopod (Dinosauria: Ornithischia) From the Upper Cretaceous Bajo Barreal Formation of Lago Colhue Huapi, Southern Chubut province, Argentina.

IBIRICU, LUCIO M.; LAMANNA, MATTHEW C.; MARTÍNEZ, RUBÉN D.; CASAL, GABRIEL A.; LACOVARA, KENNETH J.

Pittsburgh

Congreso; SVP: Reunión anual de Paleontología; 2010

Society of Vertebrate Paleontology

We describe an associated partial postcranial skeleton as the third definitive ornithopod dinosaur record from the Upper Cretaceous Bajo Barreal Formation of central Patagonia, Argentina. Specifically, the specimen was recovered from the uppermost Cretaceous (Campanian-?Maastrichtian) Upper Member of the Bajo Barreal Formation as exposed on an ephemeral island in the southeastern portion of Lago Colhué Huapi in southern Chubut Province. Identifiable skeletal elements include four partial dorsal vertebrae, three incomplete proximal caudal vertebrae, a middle caudal neural arch, a partial distal caudal vertebra, a dorsal rib fragment, the right calcaneum, and portions of the left metatarsal III and right metatarsal IV. Comparisons with corresponding elements of other ornithischians indicate that the material pertains to a medium-sized, non-hadrosaurid ornithopod. In particular, the morphology of the calcaneum is characteristic of these dinosaurian herbivores. The new discovery enhances our understanding of the latest Cretaceous continental vertebrate assemblages of central Patagonia and adds to the generally meager record of Late Cretaceous ornithischians from the Southern Hemisphere. Furthermore, it is important in constituting a representative of Ornithischia from the same general geographic region, and probably an equivalent stratigraphic unit, as two problematic members of this clade: the supposed ceratopsian Notoceratops and the fragmentary hadrosaurid Secernosaurus. The taxon represented by the new specimen may therefore have relevance for resolving the controversies surrounding the stratigraphic provenance of both of these Patagonian ornithischians and thesystematic position of Notoceratops.