Allosaurus was almost definitely an active hunter, but, like any other carnivore, it would not have been above scavenging. We do know that Allosaurus fed upon the numerous sauropods that shared its environment - Allosaurus teeth have been found embedded in Apatosaurus bones. They probably targeted young or ill sauropods most of the time, because a healthy 20+ ton adult would have been quite dangerous. When dealing with large animals, Allosaurus probably ambushed its prey and used "hit & run" tactics. In other words, it would run up to the brontosaur from behind, bite a massive chunk of flesh from its flank or a limb, and then retreat in order to avoid being crushed, or struck down by the sauropod's whip-like tail. It would then wait for the brontosaur to succumb to blood loss, and maybe deadly bacteria saturated saliva, much like a Komodo dragon's. Allosaurus may have used its powerful arms to grapple with smaller animals, such as Camptosaurus, holding the victim in place with its powerful talons while dispatching it with its jaws.
Many researchers think Allosaurus may have been a pack hunter. This is examined further on the "Intraspecific Interactions".
The Bite of Allosaurus
A recent study found that the true power behind Allosaurus' bite did not lie in the muscles of its jaws, but in its neck & reinforced skull. It would gape and cleave flesh from its prey by using its powerfully-muscled neck to wield its impact-resistant skull like an axe. This would have done far more damage than simply opening and closing its jaws.
Pursuit of Prey
It has been said that Allosaurus could not have been an effective hunter because it was too slow and too heavy. First of all, the weight factor is not really an issue here. Modern day rhinos weigh as much as 3 1/2 tonnes (only an exceptionally large Allosaurus would have been heavier) and they are capable of running at speeds in excess of 35 mph. No matter how slow Allosaurus was, most of its potential prey (Sauropods and Stegosaurs) were slower, less agile animals that often weighed many times more than Allosaurus. Keeping pace with them certainly would not have been a problem.
Another argument against Allosaurus pursuing prey was that, with its weight and short arms, it would not survive a fall if it tripped while running. Therefore Allosaurus would not risk injury to pursue prey. The results of a study conducted by Bruce Rothschild of the Arthritis Center of Northeast Ohio seem to be contrary to this idea. X-ray analysis of pathologic Allosaurus ribs showed healed injuries consistent with what one would expect if the beast had tumbled while running. So it seems Allosaurus was more resilient than proponents of the pure scavenger theory once believed.
