THE VALIDITY OF LAGOSUCHUS TALAMPAYENSIS ROMER, 1971 (ARCHOSAURIA, DINOSAURIFORMES), FROM THE LATE TRIASSIC OF ARGENTINA

AGNOLIN, FEDERICO L.; EZCURRA, MARTIN D.

Breviora

Field Museum

Año: 2019 vol. 565 p. 1 - 21

The Chanares Formation (latest Middle?earliest Late Triassic) of northwestern Argentina is part of ?the Ischigualasto?Villa Union Basin and preserves a rich fossil vertebrate record discovered by a crew of the Museum ´of Comparative Zoology (Harvard University) led by Alfred Romer. A diverse non-dinosaurian dinosauromorphassemblage has been described from this formation and includes the iconic, small-sized ??proto-dinosaur?? Lagosuchustalampayensis Romer, 1971. This species has been crucial to understand the body plan of dinosaur precursors and thehigher-level phylogenetic relationships of dinosaurs. More recently, authors considered this genus and species asnomina dubia. The aim of this contribution is to reassess the taxonomic validity of L. talampayensis. Newobservations indicate that the holotype of L. talampayensis differs from other avemetatarsalians, but not from thehypodigm of Marasuchus lilloensis, in the presence of a globose femoral head (strongly convex proximal and medialsurfaces) with a distinctly dorsal orientation and a sub-oval outline in proximal view as a result of incipient posteriorand posteromedial tuberosities. Thus, Lagosuchus talampayensis is here considered a senior synonym of ??Marasuchuslilloensis?? (Romer, 1972). Our conclusions have implications in the knowledge about early dinosauromorph diversityand the taxonomic richness of the group in the Chanares Formation