The anatomy and relationships of the Lower Permian reptileAraeoscelis

Two recently discovered skeletons of the enigmatic Lower Permian reptile Araeoscelis provide important, additional information on its osteology and permit a reassessment of its phylogenetic relationships. A combination of primitive and derived characters shared by Araeoscelis and Petrolacosaurus justifies their inclusion in the suborder Araeoscelidia as members of separate families and indicates that they represent the earliest, most primitive known stage in the adaptive radiation of the diapsid reptiles. Araeoscelis exhibits a suite of unusual cranial features resulting in a massive, sturdily constructed skull, which is interpreted as an adaptation to a specialized diet that probably included invertebrates protected by heavy exoskeletons. This theory is also used to explain the absence of a lower temporal fenestra in Araeoscelis as the result of secondary closure. Some cranial features are noted that support this hypothesis.