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Tuesday, July 30, 2013

T. rex wasn't just a scavenger

There’s a debate among paleontologists as to whether Tyrannosaurus rex was predominantly a predator or a scavenger. Did it chase down or ambush living prey like large cats, or did it seek out already dead carcasses like vultures? Researchers led by Robert DePalma II of the Palm Beach Museum of Natural History believe they have the paleontological equivalent of a smoking gun: a T. rex tooth embedded in a healed over wound in the tail bone of a hadrosaur.

To be clear, predators also scavenge. Almost any meat-eater will gladly forego the bother and risk of killing its own prey when there’s a perfectly good carcass just lying around. In contrast, true scavengers almost never set their table with a living victim. So the question is not whether T. rex ever scavenged but rather whether it also killed its own prey.

T. rex definitely had a bite that was powerful enough to subdue and kill its victims. It was also probably fast enough to run them down. However, neither of these attributes necessarily mean that it was a hunter. Physical prowess is also useful for driving other predators away from carcasses, not to mention for attracting mates.

So why is this tail wound so instructive? First, let’s state the obvious: dead animals don’t heal. If the T. rex had broken off a tooth while attempting to consume an already dead hadrosaur, the tail bone wouldn’t have healed. Because the tail had healed over, we know that the plant-eater had escaped the T. rex attack and lived long enough afterwards for the bone to heal. Second, the position of the bite, at the rear end of the victim, strongly suggests that the hadrosaur was fleeing at the time of the attack.

We still can’t say how often T. rex killed for itself. It might have mostly relied on finding the remains of other predators’ kills. Thanks to this find, we do know that it wasn’t exclusively a scavenger, which is a good thing because nobody wanted to think of T. rex that way anyway.

Photo by Daniel Schwen, 11/5/2010.

Robert A. DePalma, David A. Burnham, Larry D. Martin, Bruce M. Rothschild, & Peter L. Larson (2013). Physical evidence of predatory behavior in Tyrannosaurus rex Proceedings of the National Academy of Sciences of the United States of America DOI: 10.1073/pnas.1216534110.