An Archosauromorph diapsid from the Tarjados Formation (Early-Middle Triassic, Nw Argentina)

MARTÍN EZCURRA; AGUSTÍN MARTINELLI; LUCAS E. FIORELLI; ATILA DA ROSA; JULIA DESOJO

Diamante

Jornada; XXIX Jornadas Argentinas de Paleontología de Vertebrados; 2015

CICYTTP

The Agua de la Peña Group of the Ischigualasto−Villa Unión Basin (northwestern Argentina) documents the evolution of archosauromorph assemblages in western Gondwana during the late Middle to Late Triassic. However, the South American archosauromorph record in the aftermath of the Permo-Triassic mass extinction (Early−early Middle Triassic) is remarkably scarce and restricted to isolated bones. Here we describe a recently collected isolated second sacral vertebra and rib (CRILAR-Pv 499) from the Lower−Middle Triassic Tarjados Formation, unit that immediately underlies the Agua de la Peña Group. This specimen is identified as an archosauromorph because of the presence of a non-notochordal centrum and a bifurcated distal end of the second sacral rib. The latter feature places the new specimen as an archosauromorphmore derived than protorosaurs/tanystropheids, but more basal than archosauriforms, and more crownward than proterosuchids. In particular, this specimen resembles the non-archosauriform archosauromorphs Pamelaria, Prolacerta and early rhynchosaurs (e.g. Noteosuchus, Mesosuchus) in the presence of a squared posterior projection of the bifurcated second sacral rib. The new specimen also represents the second record of a diapsid for the Tarjados Formation and one of the oldest members of the group in the Ischigualasto−Villa Unión Basin. This specimen increases the knowledge of the taxonomic richness of Archosauromorpha in South America in the aftermath of the Permo−Triassic mass extinction.