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.