New rhadinosuchine proterochampsids from the late Middle-early Late Triassic of southern Brazil enhance the diversity of archosauriforms.

Abstract

Proterochampsidae is a clade of non-archosaurian archosauriforms restricted to the Middle to the Late Triassic of the Ischigualasto-Villa Unión Basin of Argentina and the Santa Maria Supersequence of Brazil. A reappraisal of proterochampsid specimens from the Brazilian Dinodontosaurus Assemblage Zone (AZ) of the Pinheiros-Chiniquá Sequence (late Ladinian-early Carnian) is presented here. One of the specimens was preliminary assigned to Chanaresuchus sp., whose type species comes from the Massetognathus-Chanaresuchus AZ of the Chañares Formation of Argentina. However, our revision indicates that it differs from Chanaresuchus, being more closely related to the middle-late Carnian Rhadinosuchus gracilis. We therefore propose the new taxon, Pinheirochampsa rodriguesi, to reallocate this specimen. Additionally, we present a revision of other putative Chanaresuchus occurrences in Brazil, including the only known specimen described for the Santacruzodon AZ (Santa Cruz do Sul Sequence; early Carnian), also proposing it as a new taxon: Kuruxuchampsa dornellesi. Both new species are characterized, among other features, by transverse expansion of the anterior end of the rostrum, similar to the condition present in Rhadinosuchus, but absent in Chanaresuchus, Gualosuchus, Pseudochampsa, and non-rhadinosuchine proterochampsids. These two new species expand the growing knowledge of the non-archosaurian archosauriform diversity during the Middle-Late Triassic in South America and enhance faunal and chronological comparisons between approximately coeval geological units between Argentina and Brazil.