megathere vs megatherian mammal

megathere and megatherian mammal both are nouns.

Word	Noun	Adjective	Verb	Adverb
megathere	Yes	No	No	No
megatherian mammal	Yes	No	No	No

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

megathere: gigantic extinct terrestrial sloth-like mammal of the Pliocene and Pleistocene in America
megatherian mammal: a large extinct ground sloth

Other hypernyms of megathere include megatherian, megatheriid.

megathere (noun)	megatherian mammal (noun)
gigantic extinct terrestrial sloth-like mammal of the Pliocene and Pleistocene in America	a large extinct ground sloth