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an order of fossil mammal-like reptiles that lived from the Late Carboniferous to the Permian. The animals, which ranged in size from relatively small (about 1 m) to very large (6 m), were closely related to Cotylosauria. The skull usually was high and narrow and had a small temporal depression and a large parietal opening. The teeth were conical. Only the maxillary canines were differentiated, and there were sometimes vomerine teeth. There were about 90 vertebrae, approximately two-thirds of which were caudal. In some Pelycosauria (Dimetrodon, Edaphosaurus), the spinous processes of the trunk vertebrae were greatly elongated, forming a dorsal sail. The hind limbs were longer than the forelimbs. The femur often had a developed process, the fourth trochanter, which is characteristic of animals with bipedal locomotion. (Dinosaurs also had a fourth trochanter.) Many Pelycosauria had abdominal ribs.
Pelycosauria were the parent group of higher mammal-like reptiles. Most were predators, but some were insectivorous or herbivorous. The reptiles inhabited dry land and water. Numerous remains of Pelycosauria have been found in the United States and Western Europe. Remains have also been discovered in southern Africa. In the USSR remains have been found in the northern European part, in the Urals region, and in Kazakhstan.