pterosaur vs archosaur

pterosaur and archosaur both are nouns.

Word	Noun	Adjective	Verb	Adverb
pterosaur	Yes	No	No	No
archosaur	Yes	No	No	No

As nouns, archosaur is a hypernym of pterosaur; that is, archosaur is a word with a broader meaning than pterosaur:

pterosaur: an extinct reptile of the Jurassic and Cretaceous having a bird-like beak and membranous wings supported by the very long fourth digit of each forelimb
archosaur: extinct reptiles including: dinosaurs, plesiosaurs, pterosaurs, ichthyosaurs, thecodonts

Other hypernyms of pterosaur include archosaurian, archosaurian reptile.

pterosaur (noun)	archosaur (noun)
an extinct reptile of the Jurassic and Cretaceous having a bird-like beak and membranous wings supported by the very long fourth digit of each forelimb	extinct reptiles including: dinosaurs, plesiosaurs, pterosaurs, ichthyosaurs, thecodonts