A broken T rex tooth found in another dinosaur's tail bone offers the first hard evidence that the king of all meat-eating beasts hunted live prey, US paleontologists say.
Scientists have long debated whether the fossil record really proves the legendary Tyrannosaurus rex was a ferocious hunter or just a scavenger that feasted on carcasses of the dead.
Previous discoveries of dinosaur bones in the bellies of T rex fossils, and even T rex-shaped bites out of the tails of other dinosaurs, have strongly suggested that the beast - from 66-100 million years ago - was a predator.
But paleontologists have not been able to rule out that T rex was an opportunistic scavenger, and scientists say the latest research still cannot disprove that theory.
What researchers have described in the Proceedings of the National Academy of Sciences, a US journal, is the first discovery of a broken T rex tooth in another dinosaur bone - in this case, in the vertebrae of a plant-eating hadrosaur.
"What we can tell from this, without a shadow of a doubt, is that a T rex engaged a living hadrosaur," said lead author Robert dePalma, of the Palm Beach Museum of Natural History in Florida.
"What this present specimen does, is it helps to essentially recrown the king."
The bones were uncovered in 2007 in the Hell Creek Formation, a prominent dinosaur fossil field that spans parts of Montana and North and South Dakota.
Poking out of two fused vertebrae is a major chunk of a T rex tooth - a well-preserved crown 3.75cm long.
T rex teeth were as big as bananas, and they could regrow any lost during their lifetimes, much like sharks do today, de Palma said.
The hadrosaur's bone regrew over the injury, signifying that the creature escaped and healed, maybe even living for years afterward.
But researchers say their analysis does not mean the reputed dino bully ate only living beasts - it likely ate dead remains, too.
"Like most modern large predators, it almost certainly did also scavenge carcasses," said the study.
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