Scientists have found a Tyrannosaurus rex tooth lodged in the spine of a hadrosaur, providing what may be the deciding piece of evidence in a long-running paleontological debate: Was T. rex a hunter or a scavenger?

It might seem obvious to anyone that’s been to a museum or watched “Jurassic Park” that T. rex was built to hunt prey, but scientists have long lacked for definitive proof. The fossil evidence of a Tyrannosaur diet up to this point could easily coincide with a scavenger as well as a hunter. T. rex fossils have been found with baby hadrosaur bones still preserved where the stomach once was, but there was no way to tell if the hadrosaurs were alive or dead when they were eaten.

But now, new bones dredged from the Hell Creek Formation in South Dakota show that at least one plant-eating dinosaur nearly fell prey to a hungry T. rex. Researchers discovered that one hadrosaur unearthed there had a T. rex tooth crown embedded in one of its tail vertebra.

Scientists from the Palm Beach Museum of Natural History, the University of Kansas Biodiversity Institute and the Black Hills Institute of Geological Research reported the find in the Proceedings of the National Academy of Sciences on Monday. The key piece of evidence pointing to the conclusion that T. rex hunted its meals instead of scavenging them, they say, is that the embedded tooth is surrounded by healed bone growth.

“This indicates that the prey escaped and lived for some time after the injury, providing direct evidence of predatory behavior by T. rex,” the authors wrote.

Furthermore, the position of the tooth near the end of the hadrosaur’s tail suggests that the T. rex was running after its prey. The researchers note that the hadrosaur’s escape shouldn’t be taken as a demonstration of T. rex’s poor hunting abilities. Modern predators like coyotes and lions typically fail in their hunts between 45 and 62 percent of the time, the authors wrote.

While you won’t have to readjust your image of T. rex as a hungry predator, you still may want to recalibrate your “Jurassic Park”-induced conception. There’s a lively debate right now concerning whether or not T. rex, like some dinosaurs, had feathers. There’s no clear answer just yet. While Dilong, a dinosaur closely related to T. rex, had simple feathers that were probably used for insulation, it was a smaller beast. Insulating feathers make more sense on a tiny creature, less so on a 10-ton beast like T. rex, according to Queen Mary, University of London paleontologist Dave Hone – though he does point out that the recently discovered Yutyrannus, much closer to T. rex both on the evolutionary tree and in size, also had feathers.

“The evidence for the possibility of feathers in Tyrannosaurus is piling up and my discussions with several colleagues [suggest] that a number now think the balance of probability lies with a fluffy or fuzzy Tyrannosaurus rex,” Hone wrote for the Guardian last October. “I'd put myself in that same bracket – for my money, even big, adult Tyrannosaurus more likely than not had at least some feathers on its body.”

So while a fluffy, fuzzy T. rex might not square with the popular representations of this dinosaur, it was a killer just the same.

SOURCE: DePalma et al. “Physical evidence of predatory behavior in Tyrannosaurus rex.” Proceedings of the National Academy of Sciences published online 15 July 2013.

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