plantigrade mammal vs placental

plantigrade mammal and placental both are nouns.

Word	Noun	Adjective	Verb	Adverb
plantigrade mammal	Yes	No	No	No
placental	Yes	Yes	No	No

As nouns, placental is a hypernym of plantigrade mammal; that is, placental is a word with a broader meaning than plantigrade mammal:

plantigrade mammal: an animal that walks with the entire sole of the foot touching the ground as e.g. bears and human beings
placental: mammals having a placenta; all mammals except monotremes and marsupials

Other hypernyms of plantigrade mammal include eutherian, eutherian mammal, placental mammal.

plantigrade mammal (noun)	placental (noun)
an animal that walks with the entire sole of the foot touching the ground as e.g. bears and human beings	mammals having a placenta; all mammals except monotremes and marsupials

plantigrade mammal (adjective)	placental (adjective)
	pertaining to or having or occurring by means of a placenta