A reappraisal of the taxonomic status of Aetosauroides (Archosauria, Aetosauria) specimens from the Late Triassic of South America and their proposed synonymy with Stagonolepis

摘要

The South American record of early Late Triassic aetosaurs is composed of two species: Aetosauroides scagliai and Aetosauroides subsulcatus. Previously undescribed materials belonging to Aetosauroides subsulcatus allow us to reassess its taxonomy, leading us to consider it a junior synonym of Aetosauroides scagliai. Based on the emended diagnosis of the species provided here, we recognize that specimens assignable to Aetosauroides scagliai are less common than thought previously and several of them are not diagnostic beyond indeterminate non-typothorasicine aetosaurins. Previous assignments of Aetosauroides as a junior synonym of Stagonolepis are not followed because the South American taxon is distinct due to the presence of a maxilla excluded from the external narial margin, tooth crowns with a straight distal margin and without a constriction between the root and crown, a gradually convex ventral margin of the dentary, oval fossae ventral to the neurocentral suture on the lateral sides of the centra, and a ratio between the length and the width between the distal-most tips of the postzygapophyses equal to or lower than 0.75. The evidence provided here bolsters the validity of Aetosauroides and extends the distribution of Aetosauroides scagliai into southern Brazil. Although Stagonolepis was employed as an index taxon for the Adamanian LVF, this genus is currently restricted to Europe and North America. Thus, no overlapping genera or species of aetosaur are shared between South America and other landmasses. Accordingly, the record of aetosaurs is not useful for providing biostratigraphical correlations between Late Triassic South American beds and those in other regions.