plantigrade vs placental mammal

plantigrade and placental mammal both are nouns.

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

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

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

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

plantigrade (noun)	placental mammal (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 (adjective)	placental mammal (adjective)
(of mammals) walking on the whole sole of the foot (as rabbits, raccoons, bears, and humans do)