A reappraisal of “Aetosauroides subsulcatus” (Archosauria: Aetosauria) and its synonymy with Aetosauroides scagliai

DESOJO, J.B.; EZCURRA, M.

San Rafael, Mendoza, Argentina.

Jornada; XXIV Jornadas Argentinas de Paleontología de Vertebrados; 2009

Asociación Paleontológica Argentina

The Late Triassic aetosaur record of South America is currently based on the Argentinean Aetosauroides scagliai Casamiquela and Neoaetosauroides engaeus Bonaparte, the Chilean putative Chilenosuchus forttae Casamiquela, and the Brazilian “Aetosauroides subsulcatus”. The latter taxon was described by Zacarias in 1982 as a new species of Aetosauroides (MCP-13-PV) from the Santa Maria Formation. More recently, Lucas and Heckert reviewed the taxonomy of Aetosauroides and referred both A. scagliai and “A. subsulcatus” to Stagonolepis robertsoni Agassiz. However, this taxonomic referral has not been widely followed in more recent contributions. Previously undescribed materials belonging to the type specimenof “Aetosauroides subsulcatus” allow us to reassess the taxonomy of this species. The new elements consist of a series of six articulated and well-preserved dorsal vertebrae, and several osteoderms. The presence of fossae (lateral oval depressions) below the neurocentral suture, vertebral laminae (posterior infradiapophyseal lamina), and posterolaterally divergentpostzygapophyses are characters which are exclusively shared between “Aetosauroides subsulcatus” and Aetosauroides scagliai. As a result, we suggest that “Aetosauroides subsulcatus” is a junior synonym of Aetosauroides scagliai. In addition, followingthe recent review of Aetosauroides scagliai by one of the authors (JBD), this taxon is not a junior synonym of Stagonolepis robertsoni. The new evidence provided here bolsters the validity of Aetosauroides and extends the distribution of Aetosauroides scagliai into southern Brazil. The common presence of Aetosauroides scagliai in the lower Ischigualasto Formation and the Santa Maria Formation (Alemoa Member) reinforces the biostratigraphic correlation between theseunits belonging to the Hyperodapedon-Acme Zone.