To be honest, I’m surprised that more people haven’t advocated the “Tyrannosaurus and its family were pack hunters” theory before. I mean, I know it
has been suggested before, but not nearly enough for my liking. General consensus says Tyrannosaurus was a solitary opportunist, and though that seems to be changing with the scientific community, most laypeople still think of large meat-eaters, especially the tyrant lizard king, as solitary hunters.
Personally, I’m becoming more and more convinced that there's something to the idea that if tyrannosaurs in general and Tyrannosaurus in particular hunted regularly at all (I’m not completely sold on the scavenger theory, but I haven’t totally discounted it either; of course, a scavenger could live in groups as well), they hunted in packs. As much is regularly proposed about Allosaurus, the smaller, distant relative of the Jurassic.
Of course, it’s hard to have definitive evidence of anything when you’re dealing with extinct animals you can’t actually observe and your knowledge of them is constantly changing. Most of the time, what we think we know about dinosaur behavior is composed essentially of educated guesses. But I think there’s compelling reason to believe that tyrannosaurs, like the smaller and more agile dromeosaurids, were pack animals.
Recorded head- and face-biting (link is long, very technical, requires Adobe Reader, but a good read if you have the time and patience for animals’ Latin names) in certain tyrannosaurs actually seems to suggest pack behavior, given that head- and face-biting occasionally occurs in extant animals during squabbles over a mate or dominance in the pack hierarchy.
Of course, such biting could also be indicative of packs or solitary animals fighting over territory, could be indicative of cannibalism or attempted cannibalism, or could even be play that got too aggressive. Although some possibility for intraspecific conflict exists in Tyrannosaurus itself, it’s
much less conclusive.
Still,
one Albertosaurus site contained the remains of 22 animals, including one very old animal and several juveniles, with few plant-eating dinosaurs around in the area. This seems to suggest that Albertosaurus – a relative of Tyrannosaurus – lived in groups. While not definitive proof that either Albertosaurus or Tyrannosaurus was a pack animal, it's still pretty compelling food for thought.
Tyrannosarus and its relatives may have been ambush predators, considering some people have theorized that they could not run and, given the creature’s size, it would have had trouble turning, would lend credence to the pack theory. While I don’t think it can be said, “The tyrannosaurs were pack hunters without a doubt” – I’m not sure you can say anything not directly indicated by a dinosaur’s skeleton is without a doubt – I do think it’s an intriguing idea that needs more attention.
(I am using my Aucasaurus icon because, though Aucasaurus is not a tyrannosaur, it is another large Cretaceous therapod that may have hunted in packs and so it is the best I can do.)