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
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 ...
of
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 or e ...
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
sphenacodonts 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, feeding ...
'' via a number of
transitional stages 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 no ...
s.
Classification
The following taxonomy follows Fröbisch ''et al.'' (2011) and Benson (2012) unless otherwise noted.
Class
Synapsida
* Sphenacodontoidea
** Family †
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 or e ...
**
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
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 h ...
{{Taxonbar, from=Q5853182
Transitional fossils
Extant Pennsylvanian first appearances