A uniquivocal rauisuchian from the Elliot Formation of South Africa

CHOINIERE, JONAH N.; BARRETT,E.J.; KIMBERLEY E.J. CHAPELLE; FREDERICK TOLCHARD; J.B. DESOJO; BUTLER, RICHARD J.

Bloemfontein

Simposio; 20th Palaeontological Society of Southern Africa meeting, Bloemfontein, Sudafrica.; 2018

?Rauisuchia? is a paraphyletic assemblage of primarily large-bodied, carnivorous, non-crocodylomorph pseudosuchian archosaurs whose members were relatively common components of Triassic terrestrial faunas. As they went extinct at the end of the Triassic, ?rauisuchians? can be useful biostratigraphic markers for discerning the position of the Triassic?Jurassic boundary. Surprisingly, the Late Triassic (Norian?Rhaetian) lower Elliot Formation of South Africa has never produced a definitive rauisuchian fossil, although several jaw fragments and isolated teeth have been referred to this group. The productive Elliot Formation locality Heelbo (Free State Province, South Africa) has yielded abundant remains of Early Jurassic sauropodomorph dinosaurs, including Aardonyx, Pulanesaura, and Arcusaurus. Excavations at Heelbo by our research team in 2016 recovered the articulated sacrum of a large archosaur that we initially identified as a sauropodomorph. However, preparation of the specimen revealed derived features of the ilium, including a large, dorsolaterally projecting buttress dorsal to the acetabulum, that are diagnostic for ?Rauisuchia?. Furthermore, the ilium bears strong anatomical similarities to that of Postosuchus, a member of the Late Triassic, monophyletic rauisuchian group Rauisuchidae. The new material represents the first unequivocal ?rauisuchian? from South Africa, and one of the most southerly known records for this group (~55 degrees South in the Late Triassic). The strata at Heelbo are poorly dated, but intriguingly the new fossil comes from a layer previously thought to be Early Jurassic (this level also contains Aardonyx). This means either that our find represents the only Jurassic ?rauisuchian? or that the relative age of the Heelbo strata and its fossils needs to be reassessed.