The postcranial skeleton of Luangwa sudamericana (Traversodontidae: Cynodontia) from the Middle-Late Triassic of southern Brazil

Abstract

Traversodontidae represent a highly successful lineage of Triassic Cynodontia, renowned for their taxonomic diversity and abundance. Characterized by their labiolingually expanded gomphodont postcanines, traversodontids also display a wide range of body sizes. Despite their evolutionary, paleobiological and biostratigraphy significance, studies on their postcranial anatomy remain limited. Here, we provide the first description of the postcranium of Luangwa sudamericana, based on the specimen MCN-PV 10500, recovered from the Middle-Late Triassic, Bortolin site, Santa Maria Supersequence. The specimen includes partially disarticulated vertebrae, ribs, and elements of shoulder and pelvic girdles, as well as hindlimb and forelimb bones. Specialized rib morphologies closely resembling the different stages of the ribs of the African species L. drysdalli are present. The humerus also shares comparable proportions and anatomical features with L. drysdalli. Characteristics as prominent lesser tuberosity, robust entepicondyle and supracondylar crest were observed in the humerus of MCN-PV 10500, L. drysdalli and L. sudamericana (MCN-PV 10314). Similar morphology of anterior and posterior process of the ilium, distinctive femoral greater trochanter, and anterodorsally deflected femoral head are additional similarities that support a close relationship between MCN-PV 10500 and L. drysdalli. Taphonomic and sedimentological evidence, as well as the preservation mode, suggest that the specimen was preserved in fluvial floodplain deposits, with variable bone surface preservation reflecting distinct depositional and diagenetic conditions. Although studies about the postcranial anatomy of cynodonts are quite limited the shared features of MCN-PV 10500 and L. drysdalli supports the assignment to L. sudamericana.