Debate over whether Tyrannosaurus Rex was a fierce hunter or opportunistic scavenger may finally be settled after fossil evidence of a T. rex tooth found embedded in a plant-eating dinosaur was uncovered.

The T. rex tooth was wedged into the spine of a hardosaurus, but the fossil evidence suggests that the hardodsaur's backbone had grown over the tooth, indicating that the creature healed and likely lived for years after a failed attack.

The evidence was presented Monday by a team of U.S. paleontologists, who published their work in the journal Proceedings of the National Academy of Sciences.

Previous fossil records have revealed T. rex-inflicted wounds and bones of other dinosaurs in T. rex bellies, but until now, experts were unable to rule out that the dinosaur may have been a scavenger.

"Most people assume they were predators, but the scientific evidence for predation has been really elusive," said David Burnham, preparator of vertebrate paleontology at the Biodiversity Institute at the University of Kansas. "Yes, we've found lots of dinosaur skeletons with tooth marks that had been chewed up by something. But what did that really prove? Yes, these large carnivores fed on other dinosaurs - but did they eat them while they were alive or dead? That's where the debate came in. Where was the evidence for hunt and kill?"

Burhham was approached by Robert DePalma, then a doctoral student at the University of Kansas, with an unusual fossil. After cleaning it up, it was clear the fossil belonged to a duck-billed vertebrate, and a CT scan of the specimen revealed the tooth embedded in the bone.

"What we can tell from this without a shadow of a doubt is that a T. rex engaged a living hadrosaur," DePalma, now with the Palm Beach Museum of Natural History in Florida, told the AFP.

"What this present specimen does is it helps to essentially re-crown the king," he said.

The fossils were unearthed in 2007 in the Hell Creek Formation, a prominent dinosaur fossil field that covers ground in Montana, North Dakota and South Dakota.

DePalma said the rarity of the find is "extreme."

"We never in a million years expected to find something that was this clear in the fossil record," he said.

Mark Norell, a paleontologist at the American Museum of Natural History in New York, who was not involved in the find, said, "This is smoking-gun evidence that, in fact, Tyrannosaurus did attack animals and did not just go after carrion."