Tyrannosaurus

When examining Sue, paleontologist Pete Larson found a broken and healed fibula and tail vertebrae, scarred facial bones and a tooth from another Tyrannosaurus embedded in a neck vertebra. If correct, it might be strong evidence for aggressive behavior between tyrannosaurs but whether it would be competition for food and mates or active cannibalism is unclear.[61] However, further recent investigation of these purported wounds has shown that most are infections rather than injuries (or simply damage to the fossil after death) and the few injuries are too general to be indicative of intraspecific conflict.[62] In the Sue excavation site, an Edmontosaurus annectens skeleton was also found with healed tyrannosaur-inflicted scars on its tail. The fact that the scars seem to have healed suggests active predation instead of scavenging a previous kill.[63][64] Another piece of evidence is a Triceratops found with bite marks on its ilium. Again, these were inflicted by a tyrannosaur and they too appear healed.[65]

There have been conflicting studies regarding the extent to which Tyrannosaurus could run and exactly how fast it might have been; speculation has suggested speeds up to 70 km/h (45 mph) or even more. However, according to James Farlow, a palaeontologist at Indiana-Purdue University in Fort Wayne, Indiana, "If T. rex had been moving fast and tripped, it would have died."[66] If it tripped and fell while running, a tumbling tyrannosaur's torso would have slammed into the ground at a deceleration of 6 g (six times the acceleration due to gravity, or about 60 m/s²).[5] (See also Locomotion, below.)

Some argue that if Tyrannosaurus were a scavenger, another dinosaur had to be the top predator in the Amerasian Upper Cretaceous. Top prey were the larger marginocephalians and ornithopods. The other tyrannosaurids share so many characteristics that only small dromaeosaurs remain as feasible top predators. In this light, scavenger hypothesis adherents have suggested that the size and power of tyrannosaurs allowed them to steal kills from smaller predators.