Sphenacodontoidea

{{Short description|Superfamily of synapsids}}

{{Automatic taxobox

| name = Sphenacodontoids

| fossil_range = Late Carboniferous-Recent, {{Fossil range|300|0}}

| image = NHM Sammlung - 4.jpg

| image_caption = Fossilized skull of two sphenacodontoids: Clelandina (Therapsida, Gorgonopsidae) and a Dimetrodon (Sphenacodontidae).

| display_parents = 3

| taxon = Sphenacodontoidea

| authority = Marsh, 1878

| subdivision_ranks = Clades

| subdivision =

• {{extinct}}Shashajaia
• {{extinct}}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).{{cite journal|last1=Huttenlocker|first1=A. K.|last2=Singh|first2=S. A.|last3=Henrici|first3=A. C.|last4=Sumida|first4=S. S.|year=2021|title=A Carboniferous synapsid with caniniform teeth and a reappraisal of mandibular size-shape heterodonty in the origin of mammals|journal=Royal Society Open Science|volume=8|issue=12|pages=211237|doi=10.1098/rsos.211237|pmid=34925870|pmc=8672069|bibcode=2021RSOS....811237H}} Sphenacodontoids are characterised by a number of synapomorphies concerning proportions of the bones of the skull and the teeth.{{cite journal|author=R. R. Reisz, David S Berman, Diane Scott|year=1992|url=https://www.researchgate.net/publication/227670876|title=The cranial anatomy and relationships of Secodontosaurus, an unusual mammal-like reptile (Synapsida: Sphenacodontidae) from the Early Permian of Texas|journal=Zoological Journal of the Linnean Society|volume=104|issue=2|page=127-184|doi=10.1111/j.1096-3642.1992.tb00920.x}}{{cite web|url=http://tolweb.org/notes/?note_id=466|title=Autapomorphies of the main clades of synapsids|website=Tolweb|archive-url=https://web.archive.org/web/20231027063241/http://tolweb.org/notes/?note_id=466|archive-date=October 27, 2023|url-status=live}}

The sphenacodontoids evolved from earlier sphenacodonts such as Haptodus and Ianthodon via a number of transitional stages of small, 1-10 kg, faunivore animals. 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. The first predators among Sphenacodontoidea, like Shashajaia, appeared in the tropical western part of Pangea in the Late Carboniferous. Later, in Permian, sphenacodontoids gave rise to the dominant terrestrial carnivores in both sphenacodontid and therapsid groups.