Synapsida (mammal-like reptiles; subphylum Vertebrata, class Reptilia) A subclass of reptiles which includes the Pelycosauria and Therapsida. The pelycosaurs appeared in the Upper Carboniferous and disappeared in early Permian times, displaced by the therapsids to which they had given rise. The therapsids flourished in the latter part of the Permian and in the Triassic, but dwindled to extinction in the early Jurassic. The therapsids are the ancestors of the mammals, and share in common with them a synapsid skull (i.e. a skull with one temporal opening above which the postorbital and squamosal bones meet). See also ICHTHYOPTERYGIA.

Synapsida (mammal-like reptiles; class Reptilia) Subclass of reptiles which includes the pelycosaurs (Pelycosauria) and therapsids (Therapsida). The pelycosaurs appeared in the Upper Carboniferous and disappeared in mid-Permian times, displaced by the therapsids to which they had given rise. The therapsids flourished in the latter part of the Permian and in the Triassic, but dwindled to extinction in the early Jurassic. The therapsids are the ancestors of the mammals, and share in common with them a synapsid skull (i.e. a skull with one temporal opening).

Pelycosauria (class Reptilia, subclass Synapsida) An order of reptiles, dating from the Upper Carboniferous and Lower Permian, several of which sported large, sail-like, dorsal fins. There were both carnivorous and herbivorous types. They gave rise to and were replaced by the mammal-like reptiles (Therapsida).

Pelycosauria Order of synapsid reptiles dating from the Upper Carboniferous and Lower Permian, e.g. Varanosaurus, Edaphosaurus, and Dimetrodon. Several sported large, sail-like, dorsal fins, and both carnivorous and herbivorous types appeared. They gave rise to and were replaced by the mammal-like reptiles (Therapsida).