New Crocodyliform and dinosaur discoveries from the Upper Cretaceous (Campanian-Maastrichtian?) Upper member of Bajo Barreal Formation, Southern Chubut Province, Argentina

LAMANNA, MATTHEW C.; LUNA, MARCELO; CASAL, GABRIEL A.; MARTÍNEZ, RUBÉN D.; IBIRICU, LUCIO M.; SCIUTTO, JUAN C.

St Paul; Minnesota

Congreso; SVP; Reunión anual de Paleontología; 2003

Society of Vertebrate Paleontology (SVP)

The Upper Cretaceous Bajo Barreal Formation of central Patagonia, Argentina has yielded a diverse continental vertebrate assemblage that includes chelid turtles, crocodyliforms, abelisauroid and tetanuran theropods, titanosauriform and diplodocoid sauropods, and ornithopods. The majority of these forms derive from the Cenomanian- ?Coniacian Lower Member of the Bajo Barreal. Here we report new tetrapod discoveries from the uppermost Cretaceous (Campanian-? Maastrichtian) Upper Member of the Bajo Barreal, exposed in the vicinity of Colhué Huapi in southern Chubut Province. The rostral portion of articulated mandibles characterized by a rostrocaudally elongated symphysis and marked heterodonty indicate the presence of a distinctive mesoeucrocodylian in the Upper Member fauna. The procumbent first dentary crown is labiolingually compressed and denticulate, while crowns 2-4 are ovoid in basal section. Distal crowns are globular with a denticulate distal carina and basal constriction. Dinosaur remains from the Upper Member include a fragmentary skeleton of uncertain affinities and sauropod and ornithopod material. Eighteen articulated procoelous proximal and middle caudal vertebrae and haemal arches represent a derived titanosaurian sauropod similar to Aeolosaurus, a genus widespread in the Late Cretaceous deposits elsewhere in Patagonia and Brazil. Ornithopod material consists of an isolated ilium pertaining to a derived iguanodontian, possibly a hadrosaur. If accurately identified, the latter would provide increased support for hypotheses of latest Cretaceous faunal interchange between the Americas. Further paleontological exploration of Upper Member exposures is needed to elucidate the paleobiogeographic relationships of the terminal Cretaceous tetrapod fauna of southern South America.