The validity of Lagosuchus talampayensis Romer, 1971 (Archosauria, Dinosauriformes), from the Late Triassic of Argentina

Abstract

The Chañares Formation (latest Middle–earliest Late Triassic) of northwestern Argentina is part of the Ischigualasto–Villa Unión 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 dinosauromorph assemblage has been described from this formation and includes the iconic, small-sized “proto-dinosaur” Lagosuchus talampayensis Romer, 1971. This species has been crucial to understand the body plan of dinosaur precursors and the higher-level phylogenetic relationships of dinosaurs. More recently, authors considered this genus and species as nomina dubia. The aim of this contribution is to reassess the taxonomic validity of L. talampayensis. New observations indicate that the holotype of L. talampayensis differs from other avemetatarsalians, but not from the hypodigm of Marasuchus lilloensis, in the presence of a globose femoral head (strongly convex proximal and medial surfaces) with a distinctly dorsal orientation and a sub-oval outline in proximal view as a result of incipient posterior and posteromedial tuberosities. Thus, Lagosuchus talampayensis is here considered a senior synonym of “Marasuchus lilloensis” (Romer, 1972). Our conclusions have implications in the knowledge about early dinosauromorph diversity and the taxonomic richness of the group in the Chañares Formation.