corythosaur vs corythosaurus

corythosaur and corythosaurus both are nouns.

Word	Noun	Adjective	Verb	Adverb
corythosaur	Yes	No	No	No
corythosaurus	Yes	No	No	No

As nouns, corythosaur and corythosaurus are synonyms defined as:

corythosaur and corythosaurus: duck-billed dinosaur with nasal passages that expand into a crest like a hollow helmet

corythosaur (noun)	corythosaurus (noun)
duck-billed dinosaur with nasal passages that expand into a crest like a hollow helmet	duck-billed dinosaur with nasal passages that expand into a crest like a hollow helmet