synapsid vs protomammal

synapsid and protomammal both are nouns.

Word	Noun	Adjective	Verb	Adverb
synapsid	Yes	No	No	No
protomammal	Yes	No	No	No

As nouns, protomammal is a hyponym of synapsid; that is, protomammal is a word with a more specific, narrower meaning than synapsid:

synapsid: extinct reptile having a single pair of lateral temporal openings in the skull
protomammal: probably warm-blooded; considered direct ancestor of mammals

Other hyponyms of synapsid include therapsid, ictodosaur, pelycosaur, edaphosaurus, dimetrodon.

synapsid (noun)	protomammal (noun)
extinct reptile having a single pair of lateral temporal openings in the skull	probably warm-blooded; considered direct ancestor of mammals