Reconstruction of the inner ear of the aetosaur Aetosauroides scagliai from the Upper Triassic of the Santa Maria Formation, Brazil

CARDILLO, ARIEL F.; VON BACZKO, M. BELÉN; PAES NETO, VOLTAIRE D.; DESOJO, JULIA B.

Roca

Congreso; Reunión de Comunicaciones de la Asociación Paleontologica Argentina 2023; 2023

Universidad Nacional de Rio Negro

Aetosauria is a widespread group of quadrupedal pseudosuchian archosaurs from the Upper Triassic, characterized by their heavily armored bodies. Particularly, Aetosauroides scagliai is a non-stagonolepidid aetosaur from the Upper Triassic of South America, recovered from the Ischigualasto Formation (Ischigualasto-Villa Unión Basin) in Argentina and the Santa Maria Formation (Paraná Basin) in Brazil. In this contribution, we present a novel virtual three- dimensional model of the complete inner ear of A. scagliai, obtained from micro-CT images of one of the best preserved braincases of the species (Universidade Federal de Santa Maria 11505). The semicircular canals appear slightly wider anteroposteriorly than dorsoventrally high. The inner ear of Aetosauroides scagliai shows a clear asymmetry, with a larger anterior semicircular canal and a considerably smaller posterior semicircular canal, as seen in the aetosaur Desmatosuchus species but contrasting with the symmetric inner ear of Neoaetosauroides engaeus. The anterior and posterior semicircular canal form an angle of approximately 90° in dorsal view, barely wider than in other known aetosaurs. The lateral semicircular canal is convex in dorsal view and is connected to a proportionally large anterior ampulla. The fenestra ovalis is approximately as dorsoventrally high as the common crus, delimiting a short lagena ventrally similar to that of Desmatosuchus spurensis and shorter than in Desmatosuchus smalli. In general, the morphology of the inner ear of A. scagliai resembles that of Desmatosuchus spurensis but differs on some characteristics of the semicircular canals. This new model of the inner ear of A. scagliai expands the current knowledge about the neurosensorial organs of aetosaurs, a lineage that comprises species of various feeding behaviors and body sizes, contributing to the understanding of the relationships between form and habits in this clade of pseudosuchians, an area in current exploration.