Eupelycosauria

Eupelycosauria Temporal range: Pennsylvanian–Recent, 308–0 Ma PreꞒ Ꞓ O S D C P T J K Pg N Possible Bashkirian records.
Edaphosaurus pogonias skeleton mounted at the Field Museum.
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Synapsida
Clade:	Eupelycosauria Kemp, 1982
Subgroups
†Varanopidae? Metopophora Spindler et al., 2018[1] †Ophiacodontidae Haptodontiformes Spindler et al., 2018[1] †Ianthodon †Milosaurus[2] †Kenomagnathus Sphenacomorpha Ivakhnenko, 2003 †Edaphosauridae Sphenacodontia

Eupelycosauria is a large clade of animals characterized by the unique shape of their skull, encompassing all mammals and their closest extinct relatives. They first appeared 308 million years ago during the Early Pennsylvanian epoch, with the fossils of Echinerpeton and perhaps an even earlier genus, Protoclepsydrops, representing just one of the many stages in the evolution of mammals,^[3] in contrast to their earlier amniote ancestors.

Eupelycosaurs are synapsids, animals whose skull has a single opening behind the eye. They are distinguished from the Caseasaurian synapsids by having a long, narrow supratemporal bone (instead of one that is as wide as it is long) and a frontal bone with a wider connection to the upper margin of the orbit.^[4] The only living descendants of basal eupelycosaurs are the mammals.

The group was originally considered a suborder of pelycosaurs or "mammal like reptiles",^[5] but it was redefined in 1997, and the term pelycosaur itself has fallen into disfavor. We now know that the eupelycosaurs were not in fact reptiles nor of reptile lineage - the modern term stem mammal is used instead. Some recent studies suggested that one of its subgroups, Varanopidae, are really nested within sauropsids,^[6][7][8] leaving the other defined subgroup of it, Metopophora, as its synonym.