Osteology of the temnospondyl Neldasaurus and the evolution of basal dvinosaurians

The morphology of the Lower Permian genus Neldasaurus, a long-snouted dvinosaurian temnospondyl from the Texas Red Beds, is revised. The elongate skull is characterized by medially placed nares and a wide premaxilla-maxilla contact, and large vomerine fangs penetrating the mandible. A range of features is more consistent with other dvinosaurians than previously assumed: The otic region retains a well-defined squamosal embayment, the choana is wide oval, the vomerine fangs are aligned transversely rather than parasagittally, but the contact between the pterygoid and the vomer remains unsettled. The preorbital region is highly autapomorphic and indicates a secondary elongation of the snout. According to a cladistic analysis of dvinosaurian intrarelationships, Neldasaurus is found to nest with Trimerorhachis, together forming the sister taxon of the Dvinosauroidea (Erpetosaurus, Isodectes, Acroplous, Dvinosaurus, Tupilakosaurus, Thabanchuia, and Slaugenhopia).