| Eupelycosauria | |
|---|---|
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| Edaphosaurus pogonias skeleton mounted at theField Museum | |
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| Cutleria wilmarthi | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Synapsida |
| Clade: | Eupelycosauria Kemp, 1982 |
| Subgroups | |
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Eupelycosauria is a largeclade of animals characterized by the unique shape of theirskull, encompassing allmammals and their closest extinct relatives. They first appeared 308 million years ago during theEarly Pennsylvanian epoch, with the fossils ofEchinerpeton and perhaps an even earlier genus,Protoclepsydrops, representing just one of the many stages in the evolution of mammals,[3] in contrast to their earlieramniote ancestors.
Eupelycosaurs aresynapsids, animals whose skull has a singleopening behind the eye. They aredistinguished from theCaseasaurian synapsids by having a long, narrowsupratemporal bone (instead of one that is as wide as it is long) and afrontal bone with a wider connection to the upper margin of theorbit.[4] The only living descendants of basal eupelycosaurs are themammals.
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 termstem mammal is used instead. Some recent studies suggested that one of its subgroups,Varanopidae, are really nested withinsauropsids,[6][7][8] leaving the other defined subgroup of it,Metopophora, as its synonym.
Many non-therapsid eupelycosaurs were the dominant land animals from the latestCarboniferous to the end of theEarly Permian epoch.Ophiacodontids were common from their appearance in the lateCarboniferous (Pennsylvanian) to the early Permian, but they became progressively smaller as the early Permian progressed. Theedaphosaurids, along with thecaseids, were the dominantherbivores in the early part of the Permian. The most renowned edaphosaurid isEdaphosaurus, a large [10–12-foot-long (3.0–3.7 m)] herbivore which had a sail on its back, probably used for thermoregulation and mating.Sphenacodontids, a family of carnivorous eupelycosaurs, included the famousDimetrodon, which is sometimes mistaken for adinosaur, and was the largest predator of the period. LikeEdaphosaurus,Dimetrodon also had a distinctive sail on its back, and it probably served the same purpose - regulating heat. Thevaranopid family passingly resembled today'smonitor lizards and may have had the same lifestyle.[9]
Therapsids descended from a clade closely related to the sphenacodontids. They became the succeeding dominant land animals for the rest of the Permian, and in the latter part of theTriassic, descendants of thecynodonts, an advanced group of therapsids, gave rise to the first truemammals. All non-therapsid synapsids, including all basal eupelycosaurs, as well as many other life forms,became extinct at the end of Permian period.
The followingcladogram is modified from Huttenlockeret al. (2021):[10]
| Synapsida |
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