Paleontologist David Burnham and others at the Kansas University Biodiversity Institute have found what they believe is conclusive proof that the Tyrannosaurus rex was indeed a predator and not just a scavenger. Burnham is holding a cast of a fossil from a section of a hadrosaur backbone, which has a TRex tooth embedded within it. The fossil was found in the Hell Creek formation in South Dakota by a student of Burnham's.

The embedded tooth can be seen at the center of the core of the fossil cast.

This sketch by Robert DePalma depicts the attack that may have resulted in the tooth of a Tyrannosaurus rex becoming lodged in the vertebrae of a hadrosaur, or duck-billed dinosaur. DePalma, who earned a master's degree from Kansas University in 2010, discovered a hadrosaur fossil with a T. rex tooth embedded inside, confirming that the T. rex was a predator, not a scavenger that fed on already-dead animals. A journal article describing the discovery, by DePalma and several other KU researchers, was published this week.

You might not guess it if you’ve watched “Jurassic Park,” but for about 100 years, some paleontologists have argued that the famed dinosaur Tyrannosaurus rex was actually a scavenger that fed on carcasses, not the fearsome predator many imagine.

But now there’s no doubt that the T. rex was at the top of the dinosaur food chain, a group of Kansas University researchers says. They’ve discovered evidence that the T. rex was indeed a killer.

“The monster is real,” said David Burnham, a paleontologist at KU’s Biodiversity Institute.

Burnham, a preparator for the vertebrate paleontology lab, was one of four KU researchers, including the late paleontologist Larry Martin, to contribute to an article on the discovery published today in the journal Proceedings of the National Academy of Sciences.

Their clue came from a fossil from a different dinosaur: two connected vertebrae from a hadrosaur, sometimes called a “duck-billed” dinosaur.

Robert DePalma, then a KU graduate student, brought the fossil to Burnham several years ago after he collected it from the Hell Creek formation in South Dakota, an area fertile with dinosaur fossils. DePalma, who now works at the Palm Beach Museum of Natural History in Fort Lauderdale, Fla., asked Burnham why the vertebrae had formed an odd lump, wondering if perhaps the bone had been diseased.

But after they’d blasted the mud and debris off the fossil, they saw that the two vertebrae had fused together because a tooth was lodged between them, causing the bones to heal around it.

That suggested that whatever had left its tooth there had attacked the hadrosaur while it was still alive.

“We said, ‘Well, wouldn’t it be neat if it was a T. rex?’ ” Burnham said.

If it was, the implication would be that the T. rex was indeed a hunter, not a scavenger.

Burnham and the other KU researchers already believed that was the case. But for the last century, some paleontologists had questioned the T. rex’s status as the “apex predator,” the top of the food chain, of its environment about 66 million years ago, he said. They proposed that it was too big, too slow and too fragile to chase down and catch live prey.

“It was debatable, because there wasn’t definitive evidence,” Burnham said. “We would find bones that had been bitten and chewed, and opponents just said, well, that was evidence of scavenging.”

Knowledge about exactly how 65 million-year-old dinosaurs behaved is hard to come by, Burnham said.

And when they measured the tooth its serrations — which serve as a fingerprint-like indicator that can identify a dinosaur by species — they found that it did come from a T. rex.

As DePalma put it, according to Burnham: “We crowned the king.” The T. rex had hunted down a piece of live prey, and it had attacked fiercely enough to lodge a tooth in its backbone, even if it somehow escaped.

“We thought it, or we believed it. Now we know it,” said Bruce Rothschild, one of the paper’s other authors.

Rothschild, a KU research associate as well as a professor of medicine at Northeast Ohio Medical University, used a CT scan conducted at Lawrence Memorial Hospital to confirm that the tooth was from a T. rex.

The article is one of several authored partly by Martin that have been or will be published after his death. A prolific researcher, he also contributed to a book that’s still to be released and left a number of other projects unfinished that Burnham hopes will be picked up by others.

“We like the idea that papers are still coming out with Larry’s name on it,” Burnham said. “He was such a big force in paleontology.”

Now, thanks to his and others’ work, any child — or adult — who has imagined the T. rex as the most fearsome of dinosaurs can continue to do so.

“You look at this hadrosaur vertebra with this tooth in it, and it’s kind of chilling,” Burnham said. “I mean, these things could chase you and eat you.”