Redescription of the holotype of Chanaresuchus bonapartei Romer, 1971 (Archosauriformes: Proterochampsidae) from the Upper Triassic Cha~nares Formation of north-western Argentina

Abstract

Proterochampsids are one of the several diapsid groups that originated, flourished and became extinct during theTriassic Period. The current fossil record of this group indicates that its species were restricted to continentalassemblages of the early Late Triassic of South America. The recent description of new rhadinosuchine proterochampsidspecimens from the Cha~nares Formation (early Carnian, Argentina) increased the morphological diversity of the groupand cast doubts on their current taxonomic scheme. Previous authors have pointed out that available diagnoses do notallow specimens to be referred unambiguously to the different rhadinosuchine species. Here we redescribe, figure andcompare in detail the holotype of one of these rhadinosuchine species, Chanaresuchus bonapartei from the Cha~naresFormation. The new information provided here allows us to discuss the degree of post-mortem deformation present inthe specimen and check the character scorings for the proterochampsid species sampled in the most comprehensivephylogenetic data set currently available for Permo?Triassic archosauromorphs. Our new cladistic analyses find strongersupport than previous studies for the monophyly of Rhadinosuchinae and the clades that includeDoswelliidaeþProterochampsidae and Tropidosuchus þ Rhadinosuchinae. Doswelliids are recovered withinProterochampsidae, as the sister taxon to the genus Proterochampsa, in some analyses under implied weights. Somecharacters present a phylogenetic signal consistent with the latter grouping, but one additional step is required to force itin the analysis under equal weights. We consider that the new anatomical and phylogenetic information provided here isa step towards a necessary taxono