Sphenacodontoidea is a node-based clade that is defined to include the

most recent common ancestor In biology and genetic genealogy, the most recent common ancestor (MRCA), also known as the last common ancestor (LCA) or concestor, of a set of organisms is the most recent individual from which all the organisms of the set are descended. The ...

Sphenacodontidae Sphenacodontidae (Greek: "wedge point tooth family") is an extinct family of small to large, advanced, carnivorous, Late Pennsylvanian to middle Permian pelycosaurs. The most recent one, ''Dimetrodon angelensis'', is from the late Kungurian ...

and

Therapsid Therapsida is a major group of eupelycosaurian synapsids that includes mammals, their ancestors and relatives. Many of the traits today seen as unique to mammals had their origin within early therapsids, including limbs that were oriented mor ...

a and its descendants (including mammals). Sphenacodontoids are characterised by a number of

synapomorphies In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to hav ...

concernin
proportions of the bones of the skull and the teeth
The sphenacodontoids evolved from earlier

sphenacodont 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 ...

s such as ''

Haptodus ''Haptodus'' is an extinct genus of basal sphenacodont, member of the clade that includes therapsids and hence, mammals. It was at least in length. It lived in present-day France during the Early Permian. It was a medium-sized predator, feedin ...

'' via a number of

transitional stages Transition or transitional may refer to: Mathematics, science, and technology Biology * Transition (genetics), a point mutation that changes a purine nucleotide to another purine (A ↔ G) or a pyrimidine nucleotide to another pyrimidine (C ↔ ...

of small, unspecialised

pelycosaur Pelycosaur ( ) is an older term for basal or primitive Late Paleozoic synapsids, excluding the therapsids and their descendants. Previously, the term ''mammal-like reptile'' had been used, and pelycosaur was considered an order, but this is now ...

Classification

The following taxonomy follows Fröbisch ''et al.'' (2011) and Benson (2012) unless otherwise noted. Class Synapsida * Sphenacodontoidea ** Family †

** Therapsida

References

* Laurin, M. and Reisz, R. R., 1997
Autapomorphies of the main clades of synapsids
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Tree of Life Web Project The Tree of Life Web Project is an Internet project providing information about the diversity and phylogeny of life on Earth. This collaborative peer reviewed project began in 1995, and is written by biologists from around the world. The site ...

{{Taxonbar, from=Q5853182 Transitional fossils Extant Pennsylvanian first appearances

Classification

See also

References