Pentasaurus

Pentasaurus is an extinct genus of dicynodont of the family Stahleckeriidae, closely related to the well known Placerias. It was found in the Lower Elliot Formation of South Africa, dated to the Norian of the Late Triassic period. The genus contains the type and only species, Pentasaurus goggai. Pentasaurus is named after the ichnogenus Pentasauropus, fossil footprints that were originally described from the lower Elliot Formation in 1970 decades before the body fossils of Pentasaurus itself were recognised. Pentasauropus footprints were likely made by dicynodonts, and in South Africa Pentasaurus itself was the likely trackmaker. The name reflects the fact that a large dicynodont was predicted to have existed in the lower Elliot Formation before any body fossils were recognised, and so Pentasaurus was named after its probable footprints. This is a reversal of the more typical occurrence where fossil footprints are named after their presumed trackmakers. The name of the species honours its collector Alfred Brown, nicknamed "Gogga", which means "bug" in Afrikaans.

Pentasaurus is also unique for being one of the only known dicynodonts to have coexisted with large-bodied sauropodomorph dinosaurs. Prior to its discovery, large sauropodomorphs and dicynodonts were thought to have never ecologically coexisted, with dicynodonts either going extinct prior to large sauropodomorphs evolving or being outcompeted and driven to extinction by the herbivorous dinosaurs. Pentasaurus challenges these assumptions, suggesting that dicynodonts and large sauropodomorphs could be contemporaneous, and may instead have been separated through habitat and dietary preferences. Furthermore, Pentasaurus expands the range of stahleckeriid dicynodonts in the Late Triassic into South Africa, refuting ideas that dicynodonts were geographically restricted by the Late Triassic.