syn·​ap·​sid | \ sə-ˈnap-səd How to pronounce synapsid (audio) \

Definition of synapsid

: any of a subclass (Synapsida) of terrestrial vertebrates (such as the pelycosaurs and therapsids) having a single pair of lateral temporal skull openings

Note: Traditional classifications typically consider synapsids to be mammal-like, extinct reptiles ancestral to mammals. Cladistic classifications also consider these extinct forms ancestral to mammals but do not categorize them as reptiles.

Other Words from synapsid

synapsid adjective

Examples of synapsid in a Sentence

Recent Examples on the Web At the end of the Permian, there was a sort of bottleneck that caused only smaller synapsids to survive into the Triassic. John Wenz, Popular Mechanics, 22 Nov. 2018 Four-limbed vertebrates were becoming more diverse and among them were primitive amphibians, early reptiles and synapsids, the group that would one day include mammals. Fox News, 23 Jan. 2011

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'synapsid.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

First Known Use of synapsid

1940, in the meaning defined above

History and Etymology for synapsid

New Latin Synapsida, from Greek syn- + apsid-, apsis arch, vault — more at apsis

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Time Traveler for synapsid

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The first known use of synapsid was in 1940

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Cite this Entry

“Synapsid.” Dictionary, Merriam-Webster, Accessed 25 Sep. 2022.

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