Sphenacodontoidea is a
node-based clade
A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...
that is defined to include the
most recent common ancestor of
Sphenacodontidae 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 more ...
a and its descendants (including
mammal
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...
s). 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 have ...
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'' via a number of
transitional stages of small, unspecialised
pelycosaurs.
Classification
The following taxonomy follows Fröbisch ''et al.'' (2011) and Benson (2012) unless otherwise noted.
Class
Synapsida
* Sphenacodontoidea
** Family †
Sphenacodontidae
**
Therapsida
See also
*
Evolution of mammals
The evolution of mammals has passed through many stages since the first appearance of their synapsid ancestors in the Pennsylvanian sub-period of the late Carboniferous period. By the mid-Triassic, there were many synapsid species that looked l ...
References
*
Laurin, M. and
Reisz, R. R., 1997
Autapomorphies of the main clades of synapsids-
Tree of Life Web Project
{{Taxonbar, from=Q5853182
Transitional fossils
Extant Pennsylvanian first appearances