Why Did Tyrannosaurus Have Such Small Front Legs?

Tyrannosaurus had powerful back legs to carry it long distances in search of food, sharp teeth and powerful jaws to tear it with and the size to scare its enemies. If it was a scavenger rather than a killer it had no need of large forelegs as well. There are many unanswered questions about tyrannosaurs, like the usefulness of their underdeveloped forelegs. Allosaurus, the largest Jurassic carnivore, had mighty, three-toed forelegs, which it used in hunting its prey. By comparison a tyrannosaur's tiny, two-toed forelegs must have been useless for hunting, which suggests the possibility that it was more a scavenger than a killer.