You and I say yuk to cannibalism, but for some species, it’s normal to eat their own. Crocodiles and lions will eat their young–or somebody else’s young.
A lion will kill and eat the offspring of another lion so that it can then mate with the newly available females. It’s one way of making sure your genes get passed on and the other guys don’t.
With dinosaurs, though, a more likely reason would be simple starvation–food was pretty scarce in the late Cretaceous Period, especially for big critters like T. Rex. But this is only speculation.
There is, however, some evidence to chew on–new studies of backbones found in Madagascar that once belonged to Majungatholus Atopus.
The Majungatholus is a close relative of T. Rex, and it lived about seventy million years ago. The backbones have long striations on them, consistent with having been scarred while the animal’s meat was being torn off. Guess what kind of teeth match the bite marks?
The Majungatholus Atopus. It’s strong evidence that animals in the T. Rex family may have been cannibals. Of course, we don’t know if they actually hunted each other or just scavenged anything dead.