It's been some years now that paleontologists have been volleying back and forth the idea that Tyrannosaurus rex, the biggest (ok, there are a couple other dino-predators in the same size range), meanest-looking carnivore ever to stomp the earth, was primarily a scavenger. Among the points cited are the small forelimbs and analyses indicating it wasn't fast enough to chase prey.
One researcher at the University of Alberta says this latter point isn't correct. He looked at the tail structure of T. rex vs. modern analogues like the komodo dragon and concluded the dino's tail was much more muscular than people had been assuming. The muscles at the base of the tail is a clue to how much muscle there was in the thighs, and together they can give us an idea how fast the animal moved. The answer: fast enough to run prey down, and faster than needed for a scavenger.
COMMENT: All predators will scavenge whenever the opportunity arises, but I never liked the arguments that T. rex did so almost exclusively. The animal is just over-equipped, ridiculously big and well-armed, for the job.