brontosaur vs brontosaurus

brontosaur and brontosaurus both are nouns.

Word	Noun	Adjective	Verb	Adverb
brontosaur	Yes	No	No	No
brontosaurus	Yes	No	No	No

As nouns, brontosaur and brontosaurus are synonyms defined as:

brontosaur and brontosaurus: huge quadrupedal herbivorous dinosaur common in North America in the late Jurassic

Other synonyms of brontosaur include apatosaur, apatosaurus, Apatosaurus excelsus, thunder lizard.

brontosaur (noun)	brontosaurus (noun)
huge quadrupedal herbivorous dinosaur common in North America in the late Jurassic	huge quadrupedal herbivorous dinosaur common in North America in the late Jurassic