There is a glitch on single player where if you find a pack of 3 allos, two will be stuck inside each other, while one is still running around. If you go and hit the two that are stuck with anything, they will both despawn. This is useful because then you are left with one to tame. Warning if you run into to them with out hitting them they will dislodge and attack you.

More Allosaurus Encountering Tips