class Aves vs subclass Archaeornithes

class Aves and subclass Archaeornithes both are nouns.

Word	Noun	Adjective	Verb	Adverb
class Aves	Yes	No	No	No
subclass Archaeornithes	Yes	No	No	No

class Aves (noun)	subclass Archaeornithes (noun)
(ornithology) the class of birds	primitive reptile-like fossil birds of the Jurassic or early Cretaceous