Sphenacodontia

Sphenacodontia Temporal range: Late Pennsylvanian-Recent, 304–0 Ma PreꞒ Ꞓ O S D C P T J K Pg N
3D restoration of Dimetrodon grandis, a sphenacodontid
Restoration of a pair of Alopecognathus angusticeps, a therocephalian therapsid
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Synapsida
Clade:	Sphenacomorpha
Clade:	Sphenacodontia Romer & Price, 1940
Subgroups
†Haptodus[1] †Hypselohaptodus[1] †Ianthodon[2] Pantherapsida Spindler, 2016[3] †Kenomagnathus †Tetraceratops †Palaeohatteriidae Sphenacodontoidea †Shashajaia †Sphenacodontidae Therapsida

Sphenacodontia is a stem-based clade of derived synapsids. It was defined by Amson and Laurin (2011) as "the largest clade that includes Haptodus baylei, Haptodus garnettensis and Sphenacodon ferox, but not Edaphosaurus pogonias".^[4] They first appear during the Late Pennsylvanian (Upper Carboniferous) epoch. From the end of the Carboniferous to the end of the Permian, most of them remained large, with only some secondarily becoming small in size.

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 (even though there is almost a 30-million-years gap between the separation of the ancestors of therapsids from other sphenacodontians and the first appearance of therapsids in the fossil record).