Daspletosaurus is remarkably similar to Tyrannosaurus with the main differences being smaller but heavier build, the feet shorter and the teeth proportionally larger. This has led some to conclude that Daspletosaurus was the ancestor of Tyrannosaurus, while others consider it to be a subspecies, although no definitive Tyrannosaurus remains have been found to date from the same time as Daspletosaurus.
Daspletosaurus is a possible contender for social interaction leading to pack hunting. At least two skulls show tooth marks that were inflicted on the face, with one of the skulls belonging to a juvenile showing that the tooth marks had healed over, indicating that the bite was not intended to be fatal. Face biting occurs in other predators and can relate to a number of reasons including dominance over a group subordinate, territorial dominance, or possibly even being inflicted during the mating process. An alternative explanation however is that these marks were caused by an ailment such as a parasitic infection.