REVIEW OF TWO PROTEROCHAMPSIAN SPECIMENS (ARCHOSAURIFORMES) FROM THE MIDDLE TRIASSIC OF BRAZIL (SANTA MARIA 1 SEQUENCE; DINODONTOSAURUS AZ)

RAUGUST, T.; SCHUTLZ, C. L.; EZCURRA, M. D.

Gramado

Congreso; XXIII Congresso Brasileiro de Paleontologia; 2013

Proterochampsians are non-archosaurian archosauriforms restricted to the Middle and Upper Triassicof Argentina (Ischigualasto Villa-Union Basin) and Brazil (Paraná Basin). The members of this group(i.e. Cerritosaurus, Proterochampsa, Tropidosuchus, Gualosuchus, Chanaresuchus andRhadinosuchus) are carnivorous and medium-sized quadruped forms reminiscent to extantcrocodilians, suggesting a semiaquatic lifestyle. Here we present a preliminary reevaluation of two269almost complete skulls from the Middle Triassic Santa Maria 1 Sequence (Dinodontosaurus AZ).These specimens (UFRGS-PV-0464-T and UFRGS-PV-065-T) were preliminarily assigned toChanaresuchus sp. by Dornelles (1995) and Kischlat (1996), respectively. However, both possess acombination of characters that is not present in Chanaresuchus, but some of them are presentelsewhere among other proterochampsians. The premaxillae are very laterally expanded in front oftheir suture with the maxilla, a character previously proposed as an autapomorphy of Proterochampsa.The maxillae possess a laterally inflated anterior process, resembling the condition described inRhadinosuchus. The prefrontals are strongly laterally expanded and widely convex laterally in dorsalview, as occurs in Tropidosuchus, Cerritosaurus and Gualosuchus. The maximum preserved length ofthe infratemporal fenestra is greater than that of the orbit, contrasting with Tropidosuchus. WithinProterochampsia, UFRGS-PV-0464-T and UFRGS-PV-065-T differ from other members of the groupby the presence of sub-triangular orbit with a dorsoventrally deep anterior process of jugal (ventraledge of the orbit is drop-shaped). These new data indicate that the taxonomic resolution withinProterochampsia is ambiguous, but the attribution of a new species based on the new specimens couldonly be made after an up-to-dated phylogenetic analysis.