sea cow vs aquatic mammal

sea cow and aquatic mammal both are nouns.

Word	Noun	Adjective	Verb	Adverb
sea cow	Yes	No	No	No
aquatic mammal	Yes	No	No	No

As nouns, aquatic mammal is a hypernym of sea cow; that is, aquatic mammal is a word with a broader meaning than sea cow:

sea cow: any of two families of large herbivorous aquatic mammals with paddle-shaped tails and flipper-like forelimbs and no hind limbs
aquatic mammal: whales and dolphins, manatees and dugongs, walruses, seals

sea cow (noun)	aquatic mammal (noun)
any of two families of large herbivorous aquatic mammals with paddle-shaped tails and flipper-like forelimbs and no hind limbs	whales and dolphins, manatees and dugongs, walruses, seals