A new tetrapod -bearing assemblage from the late Middle Triassic Chañares Formation, La Rioja Province, Argentina

FIORELLI, L. E.; EZCURRA, M. D.; TABORDA, J. R. A.; TROTTEYN, M. J.; BACZKO, M. B.; IBERLUCEA, M.; DESOJO, J. B.

Lujan

Jornada; REUNIÓN ANUAL DE COMUNICACIONES DE LA ASOCIACIÓN PALEONTOLÓGICA ARGENTINA; 2011

The Ladinian Chañares Formation is one of the most fossiliferous Middle Triassic tetrapod-bearing assemblages around the world. Its best sampledlocality is the classic Los Chañares locality which yielded hundreds of tetrapod specimens. Cynodonts are the most common elements (82%), in whichMassetognathus Romer is the most abundant taxon, and archosauriforms (13%) and dicynodonts (5%) are less numerous. During the Fall of 2011,field work was conducted in a locality, coined here as Brazo del Puma, which is situated within the dawning of the Gualo River in the upper-most levelsof the Lower Member of the Chañares Formation. Brazo del Puma formed part of a fluvial system with some meandering paleocanals in a fluvial plain,showing paleofloristic and paleofaunistic differences and diverse taphonomic attributes in each microenvironment. In this locality were recovered severalfragmentary tetrapod remains of parautochthonous origin housed at the Centro Regional de Investigaciones La Rioja. In contrast with the classicassemblage, Brazo del Puma depicts a greater proportion of dicynodonts (59%), being followed by archosauriforms (27%) and cynodonts (14%),respectively. Among the archosauriforms, we identified small specimens assigned to proterochampsids and doswelliids and a medium-sized indeterminateform. Brazo del Puma strongly differs from the classic locality in the high abundance of dicynodonts, but resembles the condition documentedin the co-eval Dinodontosaurus Assemblage Zone of southern Brazil. Accordingly, the new explorations conducted in the Chañares Formation indicatethat its tetrapod assemblages were more disparate than previously thought showing paleoecological differences between them.