The skull of Sphenacodon ferocior, and comparisons with other sphenacodontines (Reptilia: Pelycosauria)

Sphenacodon Marsh, known from the Lower Permian of New Mexico, Utah, and Arizona, is one of the best represented pelycosaurs in fossil collection, yet its skull has never been completely described. Virtually complete, disarticulated cranial remains of Sphenacodon ferocoir from the Lower Permian Cutler and Abo Formations of north-central New Mexico are described in detail for the first time. These descriptions provide the basis for the most detailed comparisons to date within the genus Sphenacodon and the subfamily Sphenacodontinae. No morphological differences exist between the skulls of Sphenacodon and Ctenospondylus , and only minor morphological differences exist between Sphenacodon and Ctenospondylus on the one hand and Dimetrodon on the other. On the basis of cranial morphology alone, Sphenacodon and Ctenospondylus appear to be more closely related than the current taxonomy reflects. Macromerion is undiagnostic below the subfamily level and materials referred to Neosaurus, Bathygnathus, and " Oxyodon " are undiagnostic below the subfamily level. The retention of all of these names except " Oxyodon " are undiagnostic as a paleogeographic conveniences, " Oxyodon " has been shown by Paton (1974) to be preoccupied, and pelycosaur material assigned to that taxon should be therefore reclassified as Sphenacodontinae incertae sedis.