herbivore vs fauna

herbivore and fauna both are nouns.

Word	Noun	Adjective	Verb	Adverb
herbivore	Yes	No	No	No
fauna	Yes	No	No	No

As nouns, fauna is a hypernym of herbivore; that is, fauna is a word with a broader meaning than herbivore:

Other hypernyms of herbivore include animal, animate being, beast, brute, creature.

herbivore (noun)	fauna (noun)
any animal that feeds chiefly on grass and other plants	a living organism characterized by voluntary movement
	all the animal life in a particular region or period