Galesphyrus capensis from the Permian of South Africa and the origin of Neodiapsida

The anatomy of the enigmatic stem-reptile Galesphyrus capensis (Middle–Late Permian, South Africa) is redescribed in detail. The validity of G. capensis is confirmed based on its holotype, but the other previously referred specimen is excluded from G. capensis based on skeletal differences. The new anatomical data described here are included in an expanded phylogenetic dataset, designed to examine the relationships of Permian reptiles. Both specimens are recovered as early-diverging members of a clade which includes Millerettidae, traditionally considered ‘parareptiles’ and Neodiapsida. Consequently, Parareptilia is paraphyletic, as Millerettidae occupies a more crownward position than any other parareptile, themselves not forming a clade. Our results also demonstrate that neodiapsids originated at least in the late Capitanian, prior to the Capitanian Mass Extinction, and highlight the diversity of Younginidae, which includes three South African taxa. The exquisitely preserved postcranium of G. capensis sheds light on postcranial evolution in Late Permian stem-reptiles, bringing additional support for sister-group relationship between millerettids and neodiapsids. Our new data on G. capensis and other stem-reptiles demonstrate that the evolutionary history of the foot was remarkably complex close to the origin of Sauria, with some of the prerequisites to the evolution of the saurian foot and gait having already appeared by the late Capitanian. These overlooked Middle and Late Permian stem-reptiles have the potential to further our understanding of the origin of the reptilian crown group.