As most anyone who went through the "dinosaur phase" in childhood already guessed Tyrannosaurus rex was a fearsome predator.
A plant-eating dinosaur found with a Tyrannosaurus rex tooth lodged in its tail has confirmed what scientists long suspected: T. rex was a predator.
The tooth was discovered in the tail of a hadrosaur that lived about 66 million years ago.
"It's the Holy Grail for a paleontologist," said study co-author David Burnham, a paleontologist at the University of Kansas. "Not only was the tooth broken off, but the tail had healed around it. That means that Tyrannosaurus rex attacked that other dinosaur." (Image Gallery: See the T. rex bite wound)
The findings were published today (July 15) in the journal Proceedings of the National Academy of Sciences.
Circumstantial evidence Although T. rex has been portrayed as the deadliest dino predator, the case for predation wasn't airtight. Even though stomach remains, a fearsome bite and body plan all suggested the imposing dinosaur attacked and ate other prey, some paleontologists proposed that T. rex was a scavenger, feasting on already dead animals but not killing its prey itself.
A few other herbivore fossils had been found with traces of T. rex bite wounds, but the evidence wasn't conclusive.
Burnham and his colleagues were excavating in the Hell Creek formation in South Dakota. During the Cretaceous Period, the area was a vast network of forested rivers, and the formation now contains myriad fossils of dinosaurs and small mammals from the period.
'Beyond a reasonable doubt' Burnham's graduate student, Robert DePalma, uncovered two fused vertebrae from the tail of a hadrosaur, likely Edmontosaurus annectens, a plant eater that munched on pine needles using scissorlike teeth.
Lodged inside the vertebrae was part of a tooth, and the area around it showed signs of healing. When the team analyzed the serrations on the tooth, they confirmed it belonged to a T. rex.
"We were able to establish beyond a reasonable doubt that that is a T.rex tooth," Burnham told LiveScience.
The T. rex likely attacked the hadrosaur, but the herbivore was able to escape, Burnham said. The healing over the tooth indicates that the hadrosaur lived awhile after the attack.
The new findings prove that the iconic dinosaur preyed on hadrosaurs.
"This is the first time we have physical evidence, and without physical evidence for predation, people always said, 'Oh yeah, T.rex could have been a scavenger,'" Burnham said.
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Image Gallery: The Life of T. Rex Image Gallery: Dinosaur Daycare Wipe Out: History's Most Mysterious Extinctions Copyright 2013 LiveScience, a TechMediaNetwork company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.