therapsid
noun
the·rap·sid thə-ˈrap-səd 
: any of an order (Therapsida) of advanced synapsid vertebrates that flourished during the Permian and Triassic periods with the last forms becoming extinct during the Cretaceous period and that are considered ancestors of the mammals
therapsid adjective
Word History
Etymology
New Latin Therapsida, from ther- mammal (from Greek thēr wild animal) + apsid-, apsis arch, vault — more at fierce, apsis
First Known Use
1912, in the meaning defined above