synapsid

noun

syn·​ap·​sid sə-ˈnap-səd 

: 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.

synapsid adjective

Examples of synapsid in a Sentence

Recent Examples on the Web

Researchers unearthed a large cache at the site, including the remains of ancient reptiles, amphibians and synapsids, the precursors to mammals. —Taylor Nicioli, CNN, 21 Mar. 2024

Life on land throughout the Permian Period, which lasted from about 298 million to 252 million years ago, was dominated by synapsids, the evolutionary precursors to mammals or protomammals. —Jeanne Timmons, New York Times, 22 May 2023

Dimetrodon was a synapsid, sometimes called a proto-mammal or a mammal-like reptile. —Gemma Tarlach, Discover Magazine, 31 May 2016

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

Word History

Etymology

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

First Known Use

1940, in the meaning defined above