A NEW SKELETON OF THE DINOSAUR PRECURSOR LEWISUCHUS ADMIXTUS ALLOWS REASSESSING THE TAXONOMY OF THE DINOSAURIFORMS FROM THE LOWER CARNIAN LEVELS OF THE CHAÑARES FORMATION (LA RIOJA PROVINCE)

NESBITT, S. J.; EZCURRA, M. D.; DESOJO, J. B.; FIORELLI, L. E.

Congreso; Reunión de Comunicaciones de la Asociación Paleontológica Argentina, Puerto Madryn, 2018; 2018

The lower Carnian levels of the Chañares Formation (Ischigualasto-Villa Unión Basin, La Rioja Province) have yielded some of the most informativedinosaur precursor species known so far. However, these species are based on partial skeletons that in several cases hamper the comparisonbetween them because of the absence of overlapping bones. The latter has generated a contentious debate about the synonym between two of thesespecies, Lewisuchus admixtus and Pseudolagosuchus major. Here, we describe a new dinosauriform partial skeleton (CRILAR-Pv 552)recently collected in the Chañares Formation that for the first time preserves previously unknown anatomical regions and allows comparisonswith other dinosauriform specimens. CRILAR-Pv 552 is referred to Lewisuchus admixtus because it possesses a proportionally large skull withrecurved teeth ankylosed to the bone and lacks a coracoid foramen. The new specimen preserves a dorsally bowed dentary with a lateroventral shelf that is identical to a dentary associated with the holotype of Lewisuchus admixtus. The latter bone has been recently reinterpreted asprobably belonging to a proterochampsid, but CRILAR-Pv 552 confirms that it instead is part of the holotype of the species. Additionally, themorphology of the new specimen is completely congruent with that of specimens of Pseudolagosuchus major, bolstering the hypothesis that thelatter species is the same as Lewisuchus admixtus. We concluded that the holotype of Pseudolagosuchus major is not diagnostic at a specieslevel, thus we propose that this species should be considered a nomen dubium, but its referred specimens can be referred to Lewisuchus admixtus.