COMMENTS ON THE PAJCHA PATA (BOLIVIA) THEROPOD TOOTH

FEDERICO A. GIANECHINI; SEBASTIÁN APESTEGUÍA

General Roca, Río Negro

Jornada; Reunión Anual de Comunicaciones de la Asociación Paleontológica Argentina; 2012

Asociación Paleontológica Argentina - Instituto de Investigaciones en Paleobiología y Geología-Universidad Nacional de Río Negro

In 1989 a dinosaur tooth (MHNC-3702) was reported from the El Molino Formation (Maastrichtian) outcropping in the locality of Pajcha Pata, close to Cochabamba, Bolivia. This is the only published theropod tooth from Bolivia, a country with a remarkable ichnological record but scarce in dinosaur bones. This tooth is characterized by a straight distal border and chisel-like denticles, approximately 3 per millimeter, with the mesial ones shorter and the distal ones rectangular and more elongated. The tooth is undoubtedly referable to a theropod but the original assignment to Coelurosauria is questioned here. The straight distal border is typical in teeth of abelisaurid theropods, and was proposed as synapomorphic for this family, as is observed in teeth of Majungasaurus Lavocat, 1955, Kryptops Sereno and Brusatte, 2008, and Skorpiovenator Canale, Scanferla, Agnolín and Novas, 2009. Chisel-like denticles, being the distal ones rectangular whereas the mesial ones are shorter and the largest; and the denticle count, are also characteristic of abelisaurid teeth. The assignment to Coelurosauria, based on the size of the specimen, is not supported here, because size is not a valid or unambiguous character for taxonomic assignment in theropod teeth. On the other side, the indicated combination of traits is not common among coelurosaurian teeth. In conclusion, the Bolivian tooth is more probably belonging to an Abelisauridae. Though expected, this record is significant paleogeographically, since it expands the presence of this group to other unreported South American regions beyond Patagonia and Brasil.