- any of various groups of mammallike reptiles of the extinct order Therapsida, inhabiting all continents from mid-Permian to late Triassic times, some of which were probably warm-blooded and directly ancestral to mammals.
- of or relating to the Therapsida.
- any extinct reptile of the order Therapsida, of Permian to Triassic times: considered to be the ancestors of mammals
- Any of a group of amniotes that emerged in the Permian Period. Therapsids developed differentiated dentition, with nipping, biting, and crushing teeth, and (unlike diapsids) had forelimbs that were more greatly developed than hindlimbs. Therapsids include the so-called mammallike reptiles of the Permian and Triassic Periods, as well as mammals. Compare anapsid diapsid synapsid.