The first record of a nyctiphruretid parareptile from the Early Permian of North America, with a discussion of parareptilian temporal fenestration

The Richards Spur Locality of Oklahoma, USA, long known for its highly diverse Early Permian terrestrial tetrapod assemblage, is particularly interesting for the presence of many endemic taxa. The parareptilian component of the assemblage, rare members of other Early Permian communities, is especially diverse at Richards Spur, consisting of six species. The newest parareptile, Abyssomedon williamsi gen. et sp. nov., consists of an articulated left jaw and various disarticulated cranial and postcranial elements. A new phylogenetic analysis of parareptiles, based on an updated modified data matrix revealed that Ab.williamsi is a member of the small clade Nyctiphruretidae. This makes Ab.williamsi the first and oldest nyctiphruretid, a clade of parareptiles otherwise known from the Middle and Late Permian of Russia, extending the age of the clade back into the Early Permian. This discovery also raises the possibility that nyctiphruretids may have dispersed from western Laurasia to eastern Laurasia. The characteristic jugal morphology of Ab.williamsi shows that it would have possessed a slender, deep, temporal emargination. The current topology of Parareptilia indicates that there was considerable variability in the patterns of lateral temporal openings amongst the various members of this clade, suggesting that there may have been multiple, independent modifications of this region of the skull.(c) 2014 The Linnean Society of London