dinosaur that existed in the Jurrasic period. The average size for one is 8.5 meters long. Some of them may have reached 12 meters in length at maximum size. "Allosaurus" means "different lizard," and these different lizards are some of the best-known dinosaurs ever, but are much less famous than the well-known Tyrannosaurus Rex. Their small arms have three fingers on their hands, unlike the Tyrannosaurus, who has two fingers on each of their hands.