New Specimen Sheds Light on the Anatomy and Taxonomy of the Early Late Triassic Dinosauriforms from the Chañares Formation, NW Argentina

EZCURRA, MARTÍN D.; NESBITT, STERLING J.; FIORELLI, LUCAS E.; DESOJO, JULIA B.

ANATOMICAL RECORD-ADVANCES IN INTEGRATIVE ANATOMY AND EVOLUTIONARY BIOLOGY

WILEY-LISS, DIV JOHN WILEY & SONS INC

Año: 2020 vol. 303 p. 1393 - 1438

1932-8486

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 speciesare based on partial skeletons that in several cases hamper the comparisonbetween them because of the absence of overlapping bones. This has generateda contentious debate during the last 20 years about the synonymybetween two of these species, Lewisuchus admixtus and Pseudolagosuchusmajor. Here, we describe a new dinosauriform partial skeleton (CRILARPv552) recently collected in the Chañares Formation that preserves previouslyunknown anatomical regions for the dinosaur precursors of this unit(e.g., premaxilla, inner ear, anterior zeugopodium) and allows comparisonswith other dinosauriform specimens. CRILAR-Pv 552 is referred toLewisuchus admixtus because it possesses a proportionally large skull, alaterally projected, shelf-like ridge on the jugal, and recurved, finely serratedmiddle?posterior maxillary and dentary teeth ankylosed to the bone,and the absence of a coracoid foramen. The new specimen preserves a dorsallybowed dentary with a lateroventral shelf that is identical to a dentaryassociated with the holotype of Lewisuchus admixtus. Additionally, themorphology of the new specimen is completely congruent with that of specimensof Pseudolagosuchus major, bolstering the hypothesis that the latterspecies is a subjective junior synonym of Lewisuchus admixtus. A preliminaryphylogenetic analysis with updated scorings for Lewisuchus admixtusfound this species at the base of Silesauridae.