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 Archaeothyris 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.

Temporal range: Pennsylvanian–Recent, 308–0 Ma
Examples of eupelycosaurians : Edaphosaurus, Dimetrodon (two pelycosaurs), Inostrancevia, Moschops, Castorocauda, Adelobasileus (four therapsids including two mammaliamorphs), Panthera tigris and Bos taurus (two mammals).
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Clade: Synapsida
Clade: Eupelycosauria
Kemp, 1982

The group includes most pelycosaurs and all therapsids, the only surviving members of which are the mammals.[4] Eupelycosaurs are synapsids, animals whose skull has a single opening behind the eye. They are distinguished from the Caseasaurian pelycosaurs 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 group was originally a suborder of pelycosaurs,[5] but it was redefined in 1997.


Many non-therapsid eupelycosaurs were the dominant land animals from the latest Carboniferous to the end of the Early Permian 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 herbivores in the early part of the Permian, ranging from the size of a pig to the size of a rhinoceros. The most renowned edaphosaurid is Edaphosaurus, 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 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 varanopid family passingly resembled today's monitor lizards and may have had the same lifestyle.[6]

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, therapsids gave rise to the first true mammals. All non-therapsid pelycosaurs, as well as many other life forms, became extinct at the end of Permian period.


Archaeothyris belongs to the family Ophiacodontidae and appears in the Early Pennsylvanian

The following cladogram follows the one found on Mikko's Phylogeny Archive.



















  1. ^ a b Spindler, F., R. Wernburg, J. W. Schneider, L. Luthardt, V. Annacker, and R. Roßler. 2018. First arboreal ‘pelycosaurs’(Synapsida:Varanopidae) from the early Permian Chemnitz Fossil Lagerstatte, SE-Germany, with a review of varanopid phylogeny. Palaontologische Zeitschrift. doi: 10.1007/s12542-018-0405-9.
  2. ^ Neil Brocklehurst & Jörg Fröbisch (2018) A reexamination of Milosaurus mccordi, and the evolution of large body size in Carboniferous synapsids, Journal of Vertebrate Paleontology, 38:5, DOI: 10.1080/02724634.2018.1508026
  3. ^ Kemp. T.S., 1982, Mammal-like Reptiles and the Origin of Mammals. Academic Press, New York
  4. ^ a b Laurin, M. and Reisz, R. R., 1997, Autapomorphies of the main clades of synapsids - Tree of Life Web Project
  5. ^ Reisz, R. R., 1986, Handbuch der Paläoherpetologie – Encyclopedia of Paleoherpetology, Part 17A Pelycosauria Verlag Dr. Friedrich Pfeil, ISBN 3-89937-032-5
  6. ^ Paleos Synapsida Archived 13 March 2006 at

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