protomammal vs synapsid reptile

protomammal and synapsid reptile both are nouns.

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

As nouns, synapsid reptile is a hypernym of protomammal; that is, synapsid reptile is a word with a broader meaning than protomammal:

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

Other hypernyms of protomammal include synapsid.

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