New information on the archosaurs from the Late Triassic fissure fills locality of Pant-y-ffynnon, Wales

113. SPIEKMAN S.N.F., EZCURRA M.D., BUTLER R.J., FRASER N.C., MAIDMENT S.C.R.

Congreso; The Palaeontological Association 65th Annual Meeting; 2021

The Late Triassic to Early Jurassic fissure fill localities of the Bristol Channel area preserve adiverse fauna of mostly small-bodied vertebrates, which has provided important insights intothe early evolution of major tetrapod groups such as mammaliaforms, rhynchocephalians,crocodylomorphs and dinosaurs. The Late Triassic site at Pant-y-ffynnon in Wales yieldsa particularly rich, but poorly understood assemblage of archosaurs, including the recentlynamed theropod dinosaur Pendraig milnerae, the cursorial crocodylomorph Terrestrisuchusgracilis, the small sauropodomorph Pantydraco caducus, and the enigmatic pseudosuchianAenigmaspina pantyffonnensis. Ongoing research has revealed several new insightsinto this fauna. Pendraig is identified as a small-sized non-coelophysid coelophysoiddinosaur. A revision of Aenigmaspina, characterized by unique, bifurcating osteoderms andconspicuously T-shaped neural spines on the cervical and anterior dorsal vertebrae, recovers this genus as the sister taxon of Erpetosuchidae + Aetosauriformes in a new phylogeneticanalysis. Finally, CT-scanning has elucidated the braincase anatomy of Terrestrisuchusgracilis, highlighting several features likely plesiomorphic to Crocodylomorpha, such as aquadrate that is not fused to the braincase. Together, these studies reveal the significance ofthe fissure fills fauna for our understanding of early archosaur evolution and diversity.