apatosaur vs apatosaurus

apatosaur and apatosaurus both are nouns.

Word	Noun	Adjective	Verb	Adverb
apatosaur	Yes	No	No	No
apatosaurus	Yes	No	No	No

As nouns, apatosaur and apatosaurus are synonyms defined as:

apatosaur and apatosaurus: huge quadrupedal herbivorous dinosaur common in North America in the late Jurassic

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

apatosaur (noun)	apatosaurus (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