synapsid

Any of a group of amniote vertebrates that first emerged in the late Permian Period, characterized by a single opening in the temporal region on each side of the skull and including the mammals along with various extinct groups more closely related to mammals than to other amniotes.

Same as synapsidan.

Pertaining to the class Synapsida, of animals which have an opening low in the skull roof behind each eye, leaving a bony arch beneath each.

Any animal (including all mammals) of the class Synapsida.

extinct reptile having a single pair of lateral temporal openings in the skull