New information on the fauna from "La Bonita" (Bajo de la Carpa-Anacleto formations boundary, Santonian to Early Campanian), Río Negro Province, Argentina

FEDERICO A. GIANECHINI; GABRIEL LIO; SEBASTIÁN APESTEGUÍA

San Rafael, Mendoza

Jornada; XXIV Jornadas Argentinas de Paleontología de Vertebrados; 2009

The Bajo de la Carpa Formation is well known since early XX century for the finding of notosuchian crocodiles and large snakes. However, dinosaurs played a minor role, and the record includes the small abelisauroid Velocisaurus unicus Bonaparte, 1991, and the titanosaur sauropod Bonitasaura salgadoi Apesteguía, 2004. The latter was collected at "La Bonita" locality, where the boundary between the Bajo de la Carpa and the overlain Anacleto formations (Santonian to Early Campanian) is represented. A new fieldtrip to the zone resulted in the discovery of isolated theropod teeth with interesting insights. The four pieces belong to archosaurs: three of them to theropod dinosaurs, and the other to a neosuchian crocodyliform. The theropod tooth MPCA 247 particularly resembles those present in the coelurosaurian Orkoraptor burkei Novas, Ezcurra & Lecuona, 2008, especially after the absence of a mesial carina, the abrupt curvature of the apical portion of the crown, and the 8-shaped basal section. The remaining theropod teeth, MPCA 249 and 251 are very similar each other, with mesial and distal carinae bearing denticles and blood grooves, bands in the lateral sides, and a straight distal edge. These characters are coherent with those of the Abelisauridae. Conversely, MPCA 246 is considered as belonging to a neosuchian crocodile, due to the presence of two derived features for this clade: circular cross section and lack of lateromedial compression, and a carinae with denticles. Although represented by isolated teeth, this finding shows a part of the faunal assemblage different from the previously known.