T. Rex Tooth Found in Dinosaur's Tail Proves Tyrannosaurus Was a Predator, Study Says

The telltale tooth of a Tyrannosaurus rex found embedded in the tail of a plant-eating dinosaur provides long-sought proof that the famous carnivore hunted and killed its prey, paleontologists announced today.

"We now have conclusive evidence that T. rex indeed engaged in predatory behavior," the team of scientists, led by Dr. David Burnham of the University of Kansas, writes in this week's issue of The Proceedings of the National Academy of Sciences.

Experts discovered the tooth sunk deep in the tail bones of a 70-million-year-old herbivorous dinosaur called Edmontosaurus annectens that had been excavated from the ancient sediments of Harding County, South Dakota.

The predator, Tyrannosaurus rex

...and the woud-be prey, Edmontosaurus annectens

Despite having suffered a deep, hard bite, though, there's not much need to pity the prey. Extensive bone growth found around the tooth shows that, after a rather nasty infection, the surrounding vertebrae in the Edmontosaur's tail grew together and closed over the wound, indicating that the animal lived long after the failed attack.

T. rex, on the other hand, snapped off the top of its tooth in its would-be victim.

Since only the crown of the tooth remained in the wound, there was no genetic material available in the tooth to test its owner's identity.

But the size, shape and density of the sharp, ridged tooth is “indistinguishable” from that of a subadult Tyrannosaurus rex, the experts write.

The T. rex tooth was found lodged in two vertebrae that fused together after the attack (Image courtesy of David A. Burnham/PNAS)

The fact that T. rex was a predator -- though not always a successful one, apparently -- may not sound like news, but scientists have long debated whether Tyrannosaurs hunted their food or scrounged on carrion and other predators' kills.

Some experts -- like famous dinosaur hunter Jack Horner of The Museum of the Rockies -- have argued that T. rex was too bulky and lumbering to have been an effective predator. Instead, this camp has claimed, Tyrannosaurs bore some distinctive features, like enlarged smell receptors, that are more typical of scavengers.

The new discovery appears to put the dispute to rest, the paleontologists say, not only cementing the reputation of Tyrannosaurus rex as a fearsome killer but also providing a new level of insight into what the systems of life in the ancient West were really like.

T. rex accounts for up to 15 percent of the animal fossils found in the American West, the authors note, so "T. rex’s role as either a scavenger or predator has a profound effect on our view of the paleoecology, because it is such a massive animal.

"As such, our view of this large theropod as a predator enables us to speculate with more confidence on more accurate paleoecological reconstructions [of the region] in the Late Cretaceous."

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Sources:

• "Physical evidence of predatory behavior in Tyrannosaurus rex,"  Proceedings of the National Academy of Sciences 

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