New occurrences of massetognathine traversodontids and chiniquodontids (Synapsida, Cynodontia) from the early Late Triassic Santacruzodon Assemblage Zone (Santa Maria Supersequence, southern Brazil): Geographic and biostratigraphic implications

Abstract

We describe the fossil content of the Carolina Soil outcrop in Vera Cruz Municipality (Rio Grande do Sul State, Brazil), which represents one of the few localities with a conspicuous fossil record in the still poorly sampled Upper Triassic Santacruzodon Assemblage Zone (Santa Cruz Sequence, Santa Maria Supersequence). The site has yielded numerous specimens of the massetognathine traversodontid Santacruzodon hopsoni (Cynodontia: Gomphodontia) with a broad range of ontogenetic stages, and a new record of the chiniquodontid cynodont Chiniquodon sp. (Cynodontia: Probainognathia). The new material improves our knowledge of the anatomy of Santacruzodon, which is based on relatively incomplete, small-sized specimens collected in the Schöenstatt outcrop (Santa Cruz do Sul Municipality). Although Chiniquodon co-occurs with Santacruzodon in the Schöenstatt outcrop, its presence is not biostratigraphically significant, as Chiniquodon has a large biochron and geographical distribution, and its phylogenetic distribution requires to be comprehensively explored. However, this chiniquodontid is poorly represented in this Assemblage Zone, in contrast with the older Dinodontosaurus Assemblage Zone. The traversodontid Santacruzodon remains an index taxon of the Santacruzodon Assemblage Zone and aspects of the knowledge of its anatomy are here improved. The Carolina Soil outcrop represents one of the few fossiliferous localities known for this AZ, which was only briefly mentioned in previous studies and has a great paleontological potential for future studies.