hadrosaur vs hadrosaurus

hadrosaur and hadrosaurus both are nouns.

Word	Noun	Adjective	Verb	Adverb
hadrosaur	Yes	No	No	No
hadrosaurus	Yes	No	No	No

As nouns, hadrosaur and hadrosaurus are synonyms defined as:

hadrosaur and hadrosaurus: any of numerous large bipedal ornithischian dinosaurs having a horny duck-like bill and webbed feet; may have been partly aquatic

Other synonyms of hadrosaur include duck-billed dinosaur.

hadrosaur (noun)	hadrosaurus (noun)
any of numerous large bipedal ornithischian dinosaurs having a horny duck-like bill and webbed feet; may have been partly aquatic	any of numerous large bipedal ornithischian dinosaurs having a horny duck-like bill and webbed feet; may have been partly aquatic