Small to large, advanced, carnivorous, Late Pennsylvanian to middle Permian "pelycosaurs".

The most recent one, Dimetrodon angelensis, is from the latest Kungurian or, more likely, early Roadian San Angelo Formation.

Several large (~3 meters) and advanced members of this group (Ctenospondylus, Sphenacodon, Secodontosaurus and Dimetrodon) are distinguished by a tall sail along the back, made up of elongated vertebral neural spines, which in life must have been covered with skin and blood vessels, and presumably functioned as a thermoregulatory device.

The clade Sphenacodontoidea is used by Laurin and Reisz 1997 to designate the most recent common ancestor of Sphenacodontidae and Therapsida and all their descendants, and is defined by certain features of the skull.

Sphenacodontidae in a cladogram after Fröbisch et al., 2011:[4] Edaphosauridae Haptodus garnettensis Palaeohatteria longicaudata Pantelosaurus saxonicus Ianthodon schultzei Cutleria wilmarthi Therapsida Secodontosaurus obtusidens Cryptovenator hirschbergeri Sphenacodon Ctenospondylus Dimetrodon