[ thuh-rap-sid ]
/ θəˈræp sɪd /


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.

Origin of therapsid

< New Latin Therapsida (1905), equivalent to Greek thēr- (stem of thḗr wild beast) + apsid- (stem of apsís arch, vault, referring to the temporal arch of the skull) + New Latin -a neuter plural ending (see -a1) Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

British Dictionary definitions for therapsid

/ (θəˈræpsɪd) /


any extinct reptile of the order Therapsida, of Permian to Triassic times: considered to be the ancestors of mammals

Word Origin for therapsid

C20: from New Latin Therapsida, from Greek thēr beast + Latin apsis arch
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Scientific definitions for therapsid

[ thə-răpsĭd ]

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.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.