Sphenacodontoidea

Sphenacodontoids Temporal range: Late Carboniferous-Recent, 300–0 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Fossilized skull of two sphenacodontoids: Clelandina (Therapsida, Gorgonopsidae) and a Dimetrodon (Sphenacodontidae).
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Synapsida
Clade:	Sphenacomorpha
Clade:	Sphenacodontia
Clade:	Pantherapsida
Clade:	Sphenacodontoidea Marsh, 1878
Clades
†Shashajaia †Sphenacodontidae Therapsida

Sphenacodontoidea is a node-based clade that is defined to include the most recent common ancestor of Sphenacodontidae and Therapsida and its descendants (including mammals).^[1] Sphenacodontoids are characterised by a number of synapomorphies concerning proportions of the bones of the skull and the teeth.^[2][3]

The sphenacodontoids evolved from earlier sphenacodonts such as Haptodus and Ianthodon via a number of transitional stages of small, 1-10 kg, faunivore animals.^[1] The possible common ancestor of sphenacodontids and therapsids was a carnivorous synapsid that reached moderate or large size and more closely resembled the land-dominant Early Permian sphenacodontids than the small Haptodus.^[2] The first predators among Sphenacodontoidea, like Shashajaia, appeared in the tropical western part of Pangea in the Late Carboniferous.^[1] Later, in Permian, sphenacodontoids gave rise to the dominant terrestrial carnivores in both sphenacodontid and therapsid groups.^[2]

The following taxonomy follows Fröbisch et al. (2011) and Benson (2012) unless otherwise noted.^[4][5]

Class Synapsida

• Sphenacodontoidea
  • Family †Sphenacodontidae
  • Therapsida

Sphenacodontoidea in a cladogram modified from Huttenlocker et al. (2021):^[1]

• Evolution of mammals

• Laurin, M. and Reisz, R. R., 1997, Autapomorphies of the main clades of synapsids - Tree of Life Web Project

• "Synapsida". Mikko's Phylogeny Archive. Archived from the original on September 3, 2007.