When T. rex met the enemy, it may have been himself

Tyrannosaurus rex may have had a surprising predator to fear: Tyrannosaurus rex.

Paleontologists from the United States and Canada discovered T. rex bones with T. rex tooth markings on them, according to a study published online Friday in the journal PLoS One.

Nicholas Longrich, the Yale University paleontologist who led the study, had been picking through dinosaur bone collections in museums, looking for signs of bites by small, scavenging mammals. Instead, he came across a T. rex bone with deep gouges that appeared to be left by a large, reptilian predator.

What creature roaming the Hell Creek Formation (named after Hell Creek near Jordan, Mont.,) could have gnawed the T. rex bone? There was only one culprit in this area 65 million years ago, the scientists said: another T. rex.

“It’s not what I was looking for, but may as well run with it,” Longrich recalled thinking.

After searching through several different collections around the continent, Longrich and colleagues from Montana, Florida and Canada turned up four bones showing the distinctive tooth damage.

As telling as the tooth marks are, it’s unclear whether Tyrannosaurus rex killed one another or picked the meat off their already-dead brethren.

Scavenging seems a likely bet, Longrich said, because teeth marks thought to be from younger, smaller T. rex were also found on the bones.

But the predators also could have fought their peers for territory — and feasted on the fallen losers.

“Pick the one you like better; I suspect both would have happened,” Longrich said.

Evidence that the king of the dinosaurs ate its brethren had not been noticed before, said Sterling Nesbitt, a paleontologist at the University of Washington who was not involved in the study. That’s because finding fossils with key evidence about their former owners’ behaviors — such as what they consumed, or how they reared their young — is rare.

For instance, analysis of how a dinosaur protected its eggs “can only be made if you find the dinosaur brooding on the nest; that’s an example of how rare it is,” Nesbitt said. “That animal had to die sitting on its eggs.”

amina.khan@latimes.com