CONICET | Buscador de Institutos y Recursos Humanos

The Ischigualasto-Villa Unión Basin is one of the most extensive Triassic rift basins located along the western margin of Gondwanaland. As part of its infilling, the Chañares Formation is represented by fluvio/lacustrine deposits containing a unique Middle Triassic non-marine tetrapod assemblage characterized by its diversity and well-preserved fossil record. It includes a variety of archosauriforms (i.e., non archosaurian archosauriforms, pseudosuchians, ornithodirans) and abundant therapsids (i.e., non-mammalian cynodonts, dicynodonts). A detailed taphonomical analysis of the Chañares assemblage developed under precise stratigraphical and paleoenvironmental control allows us to recognize two different taphonomic pathways. The attritional accumulation associated with the natural death of individuals and an extraordinary accumulation associated with a mass mortality event. This study characterizes in details both pathways and reveals that good representation of the original faunal composition is present, which permits their palaeoecological examination as a fauna. The Chañares fauna is numerically dominated by therapsids both herbivorous and carnivorous, and only a low abundance of archosauriforms are documented. The herbivorous taxa of Chañares fauna represent the 58% of the specimens, whereas the exclusive carnivorous taxa (therapsids and archosauriforms) reach 36%. The rest of the fauna is represented by the piscivorous (1%) and insectivorous/carnivorous (5%) taxa. Thus, the Ladinian Chañares Fauna present the typical dominance of therapsids documented in others Early-Middle Triassic Faunas (Puesto Viejo Group, Cerro de las Cabras Formation, etc.) but with a wide representation of the taxonomic and ecological groups.