Eupelycosauria

 ( Synapsida ) 

Eupelycosauria is a large clade of animals characterized by the unique shape of their skull, encompassing all and their closest extinct relatives. They first appeared 308million 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,Kemp. T.S., 1982, Mammal-like Reptiles and the Origin of Mammals. Academic Press, New York in contrast to their earlier amniote ancestors.

---

Taxonomy Eupelycosaurs are , animals whose skull has a single opening behind the eye. They are synapomorphy from the 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.Michel Laurin and Robert Reisz, 1997, Autapomorphies of the main clades of synapsids - Tree of Life Web Project The only living descendants of basal eupelycosaurs are the .

The group was originally considered a suborder of pelycosaurs or "mammal like reptiles",Reisz, R. R., 1986, Handbuch der Paläoherpetologie – Encyclopedia of Paleoherpetology, Part 17A Pelycosauria Verlag Dr. Friedrich Pfeil, 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, leaving the other defined subgroup of it, Metopophora, as its synonym.

---

Evolution Many non-therapsid eupelycosaurs were the dominant land animals from the latest Carboniferous to the end of the Cisuralian epoch. Ophiacodontids were common from their appearance in the late Carboniferous (Pennsylvanian) to the early Permian, but they became progressively smaller as the early Permian progressed. The edaphosaurids, along with the caseids, were the dominant in the early part of the Permian. The most renowned edaphosaurid is Edaphosaurus, a large herbivore which had a sail on its back, probably used for thermoregulation and mating. Sphenacodontidae, a family of carnivorous eupelycosaurs, included the famous Dimetrodon, which is sometimes mistaken for a dinosaur, and was the largest predator of the period. Like Edaphosaurus, Dimetrodon also had a distinctive sail on its back, and it probably served the same purpose - regulating heat. The Varanopidae family passingly resembled today's and may have had the same lifestyle.

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 the Triassic, descendants of the , an advanced group of therapsids, gave rise to the first true . All non-therapsid synapsids, including all basal eupelycosaurs, as well as many other life forms, became extinct at the end of Permian period.

---

Classification The following cladogram is modified from Huttenlocker et al. (2021):

---

External links

Post Comment