Edaphosaurus a Eupelycosaurian
The Eupelycosauria originally referred to a suborder of Pelycosaurs (Reisz 1987), but has been redefined (Laurin and Reisz 1997) to designate a clade of synapsids that includes most pelycosaurs, as well as all therapsids and mammals. They first appear during the Early Pennsylvanian epoch (i.e: Archaeothyris, and perhaps an even earlier genus, Protoclepsydrops), and represent just one of the many stages in the acquiring of mammal-like characteristics (Kemp 1982), in contrast to their earlier amniote ancestors. The defining characteristics which separate these animals from the Caseasauria (also Pelycosaurs) are based on details of proportion of certain bones of the skull. These include a long, narrow supratemporal bone (in contrast to caseasaurs where this bone is almost as wide as it is long), and a frontal bone with a wider connection to the upper margin of the orbit (Laurin and Reisz 1997).
Many non-therapsid Eupelycosaurs enjoyed dominance from the Latest Carboniferous to the end of the Early Permian epoch. Ophiacodontids dominated the Latest Carboniferous until the Permian time, but they went progressively small. The Edaphosaurids, along with the Caseids, a group of synapsids that aren't Eupelycosaurs were the dominant herbivores from the Latest Carboniferous and Early Permian. Ranging from the size of a pig to the size of rhinoceroses, some were even the size of elephants. The most renowned Edaphosaurid is Edaphosaurus, a large (10 - 12 ft long) herbivore who had a sail on its back, probably for regulating heat. Edaphosaurids's (and Caseids's) Eupelycosaur predators were the Sphenacodontids - the superpredators of the Early Permian epoch. Sphenacodonts included the famous Dimetrodon, which is sometimes mistaken for a dinosaur, was a most dangerous killer of the time. It was about the size of a large bear (10 - 13 feet long). Like Edaphosaurus, Dimetrodon also had a distinctive sail on its back, and probably had a same function - regulating heat. All these Eupelycosaurs looked like reptiles - cold-blooded, and sprawling amniotes.
The closest relatives of the Sphenacodontids, the therapsids appeared in the Early Permian. In fact, Sphenacodontids and Therapsids were part of an unranked clade called Sphenacodontia - the characteristic of the skull, narrow and enlongated. Therapsids dominated over the primitive Eupelycosaurs, and ruled the land for the rest of the Permian. Therapsids gave rise to the first mammals in the Triassic.
- Series Amniota
- Kemp. T.S., 1982, Mammal-like Reptiles and the Origin of Mammals. Academic Press, New York
- Laurin, M. and Reisz, R. R., 1997, Autapomorphies of the main clades of synapsids - Tree of Life Web Project
- Reisz, R. R., 1986, Handbuch der Paläoherpetologie – Encyclopedia of Paleoherpetology, Part 17A Pelycosauria Verlag Dr. Friedrich Pfeil, ISBN 3-89937-032-5
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