The taxonomic status and phylogenetic position of the Late Triassic Brazilian rauisuchian Prestosuchus.

DESOJO, J.B.; RAUHUT, O.W.

Bristol, Gran Bretaña

Congreso; 69th Annual Meeting Society of Vertebrate Paleontology, London, Inlaterra.; 2009

University of Bristol Bristol, United Kingdom

In the end of the 1920s, Huene excavated the first basal crurotarsan archosaurs from SouthAmerica from the Late Triassic Santa Maria Formation of southern Brazil. The materialwas subsequently described as six different taxa of “pseudosuchians”: Rauisuchus,Rhadinosuchus, Procerosuchus, Hoplitosaurus, and two species of Prestosuchus, P. loricatusand P. chiniquensis. The latter was the best represented taxon, and a complete skull withassociated axial material has subsequently been referred to it. A review of the originalmaterial of Huene showed that P. chiniquensis is a valid taxon, and Procerosuchus and theparalectotype of P. loricatus can be referred to the same taxon, whereas the lectotype of P.loricatus represents a different genus. The referred skull and axial material also represent P.chiniquensis, making it one of the best known rauisuchian taxa. A preliminary phylogeneticanalysis of basal crurotarsans recovered a monophyletic Rauisuchia, which includes twosubclades, the Rauisuchidae and the Poposauridae. The latter include Arizonasaurus asthe most basal taxon and Lotosaurus, Poposaurus, Sillosuchus, Shuvosaurus and Effigiaas more derived taxa. Within the Raisuchidae, Postosuchus represents the most basaltaxon, followed by Prestosuchus, Stagonosuchus and Saurosuchus. More derived taxainclude Batrachotomus, Ticinosuchus and Rauisuchus. Rauisuchia is supported by threeunambiguous characters, a stepped postorbital bar, a large ventral astragalocalcanealarticular facet, and large lateral fossae in the cervical vertebrae. Rauisuchidae is currently only supported by one unambiguous character, the presence of a large subnarial foramen, but rauisuchids more derived than Postosuchus share four unambiguous synapomorphies, an exposed quadrate head in lateral view, an oblique ridge on the lateral side of the squamosal, a fully closed acetabulum, and a high, crest-like iliofibularis trochanter on the fibula. The fact that one of the most derived rauisuchids known, Ticinosuchus, comes from the Middle Triassic (Anisian-Ladinian boundary),