Archosaur remains from Late Triassic beds of San Luis Province (Quebrada Del Barro Formation, Marayes-Carrizal Basin), Argentina

FEDERICO A. GIANECHINI; LAURA S. CODORNIÚ; ANDREA B. ARCUCCI; GABRIELA CASTILLO ELÍAS; GERÓNIMO CANDELA

Diamante, Entre Ríos

Jornada; XXIX Jornadas Argentinas de Paleontología de Vertebrados; 2015

In this contribution, we present tetrapod remains from the Quebrada del Barro Formation, south of Sierra de Guayaguas, NW of San Luis province. The locality was previously reported but a detailed study of the material is conducted here. The specimens were found isolated, and consist in one partial incomplete maxilla (MIC-V718), one caudal vertebra (MIC-V719) and two fragmentary metatarsals (MIC-V720, MIC-V721). The maxilla is represented by the posterior process, it is triangular in lateral view and remarkably large and robust. It preserved six alveoli and one partially erupted tooth, which is lateromedially compressed with ?chisel-like? denticles. Anatomical features and size allow its assignment to the Rauisuchia. The vertebra has a centrum larger in height than in length, with a ventral longitudinal furrow and expanded articular processes for the chevrons. The diapophysis arises at the posterior half of the neural arch and below the level of the prezygapophyses, and it is dorsoventrally compressed and posterodorsally inclined. The prezygapophyses are short and anterodorsally projected. The neural spine and postzygapophyses are missing. This caudal vertebra resembles those of sauropodomorphs. The metatarsals present slender diaphyses, one of them with well-developed distal condyles and the other with a convex and triangular distal articular surface. These metatarsals resemble those of theropods. Despite being fragmentary, these materials indicate the presence of a diverse archosaur association from Late Triassic beds of San Luis. Moreover, they evidence a faunal assemblage similar to the one recorded from coeval deposits of San Juan province and Los Colorados Formation in La Rioja.