The long bone, found in sediments dating back 66 million years, clearly shows 10 deep grooves made by serrated teeth — the first tyrannosaur bone found to have such teeth marks, paleontologists say, and the first evidence that T. rex was eaten by its own kind.
The signs of Cretaceous cannibalism were clear enough that scientists spotted them immediately in the field, according to paleontologist Matthew McLain of Loma Linda University, who reported the find.
“Someone found a tyrannosaur bone that was broken at both ends. It was covered in grooves. They were very deep grooves.”
The deep, U-shape scores were up to five millimeters wide [about a fifth of an inch] at some points, he reported.
And in addition, the scars on the bone ran perpendicular to the length of the bone, suggesting that the flesh was pulled from the T. rex bone much as meat is eaten from a chicken’s drumstick.
Moreover, at the rounded end of the bone, a set of smaller, parallel grooves was found, made as the eating animal turned its head as it pulled the flesh, leaving serrated striations behind.
The fact that the grooves were made by serrated teeth rules out animals like crocodiles, McLain said, and indeed they could only have been made by another theropod dinosaur. [See a T. rex tooth up-close]
Since the only theropods found in the Lance Formation, in north-central Wyoming, are tyrannosaurs — including T. rex and Nanotyrannus, which some scientists believe may truly be juvenile specimens of T. rex — the only conclusion is that this T. rex was cannibalized by one of its own.
“This has to be a tyrannosaur,” said McLain. “There’s just nothing else that has such big teeth.”
It’s unclear from the fossils that have been found and studied so far whether the T. rex that was eaten was killed by the other tyrannosaur, or whether it was scavenged when already dead. [See another case of dinosaur CSI: “T. Rex Tooth Found in Dinosaur’s Tail Proves Tyrannosaurus Was a Predator, Study Says“]
But the clear serrations from the teeth marks may allow future research to pinpoint which species managed to eat the famous predator.
“Exactly who did the eating that day, in the Late Cretaceous, could still be sorted out by the same grooves,” McLain said.
Specifically, the nature of the serrations can provide data about the size of the animal that made them, which in turn could settle whether the dinosaur that did the dining was T. rex or Nanotyrannus.
“It only works if you know what species it is,” McLain said.
“And since tyrannosauruses are the only large predators in these formations, it’s pretty straightforward.”
McLain reports his team’s findings at the annual meeting of the Geological Society of America in Baltimore.