Acrocanthosaurus was a large carnosaur theropod dinosaur that had a large head, many sharp teeth, strong arms, powerful back legs, and a long slender tail that balanced its body when it ran. It lived alongside the small raptor Deinonychus , some small ankylosaurs, and hunted large sauropods. Acrocanthosaurus had one feature that made it look very different from other theropods; the tall "sail" along its neck, back, and tail.