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

FIORELLI, L; EZCURRA, M; TABORDA, J R A; TROTTEYN, M J; VON BACZKO, M B; IBERLUCEA, M; DESOJO, J B

Luján

Otro; Reunión Anual de comunicaciones de la Asociación Paleontológica Argentina y Ciclo de Conferencias: ?Vida y Obra de Florentino Ameghino?; 2011

Universidad Nacional de Lujan, Asociacion Paleontologica Argentina

The Ladinian Chañares Formation crops out in La Rioja Province as part of the Ischigualasto-Villa Unión Basin. This formation is one of the most fossiliferous Middle Triassic tetrapod-bearing assemblages around the world. The best sampled locality of the unit is the Romer?s type locality which yielded hundreds of tetrapod specimens. Cynodonts are the most common elements (ca. 82%), in which Massetognathus is the most abundant taxon, and archosauriforms (ca. 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 Desembocadura del Río Gualo in the lower-most levels of the Chañares Formation. Brazo del Puma formed part of a fluvial system with paleocanals and inter-canal plains, in which were recovered several fragmentary tetrapod remains of para-authoctonous origin. In contrast with Romer?s type assemblage, Brazo del Puma depicts a greater proportion of dicynodonts (ca. 59%), being followed by archosauriforms (ca. 27%) and cynodonts (ca. 14%), respectively. Among the archosauriforms, we identified small specimens assigned to proterochampsids and doswelliids and a medium-sized indeterminate form. Brazo del Puma strongly differs from Romer?s type locality in the high abundance of dicynodonts, but resembles the condition documented in other South American units, such as the co-eval Dinodontosaurus AZ of southern Brazil. Accordingly, the new explorations conducted in the Chañares Formation indicate that its tetrapod assemblages were more disparate than previously thought.