Siriusgnathus niemeyerorum (Eucynodontia: Gomphodontia): The youngest South American traversodontid?

摘要

Traversodontidae is a less inclusive Glade of cynognathian cynodonts that lived during the Triassic. Recently, a traversodontid from the southern Brazilian Triassic beds was described - Siriusgnathus niemeyerorum - based upon specimens found exclusively in its type-locality. No absolute age or index fossils have been reported for this locality, which prevents an accurate biostratigraphic correlation. In the present contribution, we describe the first specimens of S. niemeyerorum found outside its type-locality, comprising skull portions excavated from outcrops in southern Brazil assigned to the Caturrita Formation (upper portion of the Candelaria Sequence), Upper Triassic (Norian), Riograndia Assemblage Zone. As a result, we provide an updated biostratigraphic framework and suggest a Norian age for the type-locality of S. niemeyerorum, which, accordingly, possibly comprises the youngest South American traversodontid, pending additional geochronological studies in order to properly evaluate this hypothesis.