Synapsida

plural noun

Syn·​ap·​si·​da

-psədə

: a subclass of Reptilia comprising extinct reptiles of the Pennsylvanian, Permian, and Triassic, having a single pair of lateral temporal openings in the skull, and usually held to be ancestral to the true mammals compare ictidosauria , therapsida

Word History

Etymology

New Latin, from synapsis + -ida

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