allosaur vs allosaurus

allosaur and allosaurus both are nouns.

Word	Noun	Adjective	Verb	Adverb
allosaur	Yes	No	No	No
allosaurus	Yes	No	No	No

As nouns, allosaur and allosaurus are synonyms defined as:

allosaur and allosaurus: late Jurassic carnivorous dinosaur; similar to but somewhat smaller than tyrannosaurus

allosaur (noun)	allosaurus (noun)
late Jurassic carnivorous dinosaur; similar to but somewhat smaller than tyrannosaurus	late Jurassic carnivorous dinosaur; similar to but somewhat smaller than tyrannosaurus