The Apatosaurus had many predators one of them was the allosaurs.
Scientists found an Apatosaurus vertebra was found with allosaursus teeth prints on it. This was a result of an attack.
Allosaurus was a large, fierce predator that could kill medium-sized sauropods (or sick or injured large sauropods like Apatosaurus) and many others of this kind. Allosaurus may also have been a scavenger.