ictodosaur vs synapsid reptile

ictodosaur and synapsid reptile both are nouns.

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

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

ictodosaur: intermediate in form between the therapsids and most primitive true mammals
synapsid reptile: extinct reptile having a single pair of lateral temporal openings in the skull

Other hypernyms of ictodosaur include synapsid.

ictodosaur (noun)	synapsid reptile (noun)
intermediate in form between the therapsids and most primitive true mammals	extinct reptile having a single pair of lateral temporal openings in the skull