A NEW TETRAPOD-BEARING ASSEMBLAGE FROM THE LATE MIDDLE TRIASSIC CHAÑARES FORMATION, LA RIOJA PROVINCE, ARGENTINA

FIORELLI, LUCAS E.; EZCURRA, MARTÍN D.; TABORDA, JEREMIAS R.A.; TROTTEYN, MARÍA JIMENA; VON BACZCO, M. BELÉN; IBERLUCEA, MAXIMILIANO; DESOJO, JULIA BRENDA

Luján

Otro; Reunión Anual de la Sociedad Palentológica Aregentina; 2011

Asociación Paleontológica Argenitna

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. Its best sampled locality is the classic Los Chañares locality which yielded hundreds of tetrapod specimens. Cynodonts are the most common elements (82%), in which Massetognathus 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 levels of 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 several fragmentary tetrapod remains of parautochthonous origin. In contrast with the classic assemblage, 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 indeterminate form. Brazo del Puma strongly differs from the classic locality in the high abundance of dicynodonts, but resembles the condition documented in 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 showing paleoecological differences between them.