Pronunciation: s ə - ' nap-s ə d
Function: noun
Etymology: New Latin Synapsida, from Greek syn- + apsid-, apsis arch, vault ― more at APSIS
Date: 1956
: any of a subclass (Synapsida) of extinct chiefly Permian and Triassic reptiles (as the pelycosaurs) that resembled mammals, had a single pair of lateral temporal skull openings, and are usually held to be ancestral to mammals
– synapsid adjective