reptilian vs Reptilia

reptilian and Reptilia both are nouns.

Word	Noun	Adjective	Verb	Adverb
reptilian	Yes	Yes	No	No
Reptilia	Yes	No	No	No

reptilian (noun)	Reptilia (noun)
any cold-blooded vertebrate of the class Reptilia including tortoises, turtles, snakes, lizards, alligators, crocodiles, and extinct forms	class of cold-blooded air-breathing vertebrates with completely ossified skeleton and a body usually covered with scales or horny plates; once the dominant land animals

reptilian (adjective)	Reptilia (adjective)
of or relating to the class Reptilia