T. Rex tooth embedded in fossil proves he was a predator

The Tyrannosaurus rex occupies a unique place in our cultural imagination.

Thanks to films like "Jurassic Park," the dinosaur is one of the scariest monsters we know. Thanks to its short forearms, T. rex is ripe for comedy.

So which is the real Tyrannosaurus rex?

Despite a terrifying reputation, paleobiologists weren't actually sure whether T. rex was a ferocious predator, or more of a scavenger.

Until, perhaps, now.

Researchers at the University of Kansas unearthed a fossil of the tailbone of a plant-eating hadrosaur that might put the 100-year debate to rest. Embedded between two of the tailbones, they discovered a tooth once belonging to a T. rex.

T. rex teeth are distinctive -- long, sharp and serrated, nicknamed "lethal bananas" -- and the way the hadrosaur bone had regrown around it seems to prove the would-be prey survived its encounter with rex.

"It's the bullet from the smoking gun," said paleontologist David Burnham, who, with a graduate student, found the fossil. "Here you have attempted murder, and here we are able to identify the perpetrator."

The location of the tooth in the tail is more evidence the T. rex was hunting the hadrosaur, since predators typically grab at the tail of running prey.

Still, the predators may have also feasted on carrion, Burnham and his colleagues wrote, so tooth-punctured fossils without signs of healing would not contradict the findings of this research.

Burnham said the significance of the find was apparent immediately.

"It was a very exciting moment," he said. "We felt like the king was back."

Other researchers cast doubt on Burnham's theory, suggesting alternate scenarios that would disprove it.

Montana State University paleontologist Jack Horner, who was not part of the study, said the location of the tooth, on the underside of the tail might indicate the hadrosaur was lying down when it was attacked by the T. Rex.

The study only proves the T. Rex "bit the animal, and the animal lived," Horner said. Perhaps the T. Rex mistook the hadrosaur, and abandoned it when it realized its potential meal was still alive.

But study leader Robert DePalma, a paleontologist at the Palm Beach Museum of Natural History, called Horner's scenario "implausible."

"A scavenger doesn't come across a food source and realize all of a sudden that it's alive," he said.

Short of the invention of a time machine, we may never know for sure.