An archosauromorph diapsid from the Tarjados Formation (Early-Middle Triassic, NW Argentina)

EZCURRA, M.D.; MARTINELLI, A.G.; FIORELLI, L.E.; DA-ROSA, A.A.S.; DESOJO, J.B.

Diamante

Jornada; XXIX Jornadas Argentinas de Paleontología de Vertebrados; 2015

CICYTTP

TheAgua de la Peña Group of the Ischigualasto−Villa Unión Basin (northwesternArgentina) documents the evolution of archosauromorph assemblages in westernGondwana during the late Middle to Late Triassic. However, the South Americanarchosauromorph record in the aftermath of the Permo-Triassic mass extinction(Early−early Middle Triassic) is remarkably scarce and restricted to isolatedbones. Here we describe a recently collected isolated second sacral vertebraand rib (CRILAR-Pv 499) from the Lower−Middle Triassic Tarjados Formation, unitthat immediately underlies the Agua de la Peña Group. This specimen isidentified as an archosauromorph because of the presence of a non-notochordalcentrum and a bifurcated distal end of the second sacral rib. The latterfeature places the new specimen as an archosauromorph more derived thanprotorosaurs/tanystropheids, but more basal than archosauriforms, and morecrownward than proterosuchids. In particular, this specimen resembles thenon-archosauriform archosauromorphs Pamelaria, Prolacerta andearly rhynchosaurs (e.g. Noteosuchus, Mesosuchus) in thepresence of a squared posterior projection of the bifurcated second sacral rib.The new specimen also represents the second record of a diapsid for theTarjados Formation and one of the oldest members of the group in theIschigualasto−Villa Unión Basin. This specimen increases the knowledge of the taxonomicrichness of Archosauromorpha in South America in the aftermath of thePermo−Triassic mass extinction.