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).

Synapsida