Sphenacodontia

Sphenacodontia is the name given to the clade that includes the Sphenacodontidae and all their descendants (including mammals). They first appear during the Late Pennsylvanian epoch. The defining characteristics include a thickening of the maxilla visible on its internal surface, above the large front (caniniform) teeth; and the premaxillary teeth being set in deep sockets. All other (sister group and more primitive) synapsid clades have teeth that are set in shallow sockets.

Basal Sphenacodontia constitute a transitional evolutionary series from early pelycosaurs to ancestral therapsids (which in turn were the ancestors of more advanced forms and finally the mammals). One might say that the Sphenacodontians are proto-therapsids.

Taxonomy and Phylogeny

 * Class Synapsida
 * ORDER PELYCOSAURIA
 * Suborder Eupelycosauria
 * Sphenacodontia (incl. paraphyletic Sphenacodontidae)
 * Haptodus
 * Palaeohatteria
 * Pantelosaurus
 * Cutleria
 * Sphenacodontoidea
 * Family Sphenacodontidae (sensu stricto)
 * Ctenospondylus
 * Dimetrodon
 * Secodontosaurus
 * Sphenacodon
 * Family Tetraceratopsidae
 * '''ORDER THERAPSIDA
 * '''Class Mammalia