Biostratigraphic significance of a new record of Protuberum cabralense , a bizarre traversodontid cynodont from the Middle‑Late Triassic of Southern Brazil

Abstract

Traversodontid cynodonts are one of the most abundant and diverse groups of tetrapods in the Triassic assemblages of Brazil. These cynodonts are distributed across four Brazilian Assemblage Zones (AZ), ranging from the late Ladinian to the early Norian. The most taxonomically diverse record comes from the Dinodontosaurus AZ, which has so far yielded at least six traversodontid genera. Among these taxa,Protuberum cabralense represents one of the most bizarre forms. This cynodont is characterised by thepresence of enlarged and rounded protuberances along the dorsal surface of the ribs, the vertebral neural spines and dorsal portion of the iliac blades. These structures have been suggested to serve as a defensive mechanism or related to burrowing/digging habits. We report the first occurrence of P. cabralense at the Linha Várzea 1 site, located in the municipality of Paraíso do Sul, Brazil. This site is considered late Ladinian to early Carnian in age. The new material consists of five rib fragments, which possess the characteristic protuberances on their dorsal surface. A biostratigraphic investigation demonstrates the absence of P. cabralense in fossiliferous sites that yielded the cynodonts Luangwa. This observation contributes to the discussion regarding a potential subdivision within the Dinodontosaurus AZ.