A distinctive pattern of tooth marks on a 66-million-year-old tyrannosaur bone found in eastern Wyoming offers one of the best evidences yet that tyrannosaurid dinosaurs were not shy about eating their own kind, according to a team of paleontologists led by Loma Linda University, California.

The tyrannosaur long bone was recovered from the uppermost Cretaceous Lance Formation.

“The bone was found at the surface near a thin bonebed within a sandstone unit,” explained Loma Linda University paleontologist Matthew McLain.

The grooves were clearly those of an animal pulling the flesh off the bone – pulling in a direction perpendicular to the bone, in the same way humans eat a piece of fried chicken.

“But one groove stood out. It was located at the larger end of the bone and contained smaller parallel grooves caused by the diner’s head turning, so that the serrated edges of its teeth dragged across the bone,” said McLain, who will be presenting the discovery on November 1, 2015, at the annual meeting of the Geological Society of America in Baltimore.

“Serrated teeth rule out crocodiles and point directly to a theropod dinosaur like Tyrannosaurus rex,” he said.

“The fact that the only large theropods found in the Lance Formation are two tyrannosaurs – Tyrannosaurus rex or Nanotyrannus lancensis – eliminates all interpretations but cannibalism.”

“This has to be a tyrannosaur. There’s just nothing else that has such big teeth,” McLain said.

The direction of the grooves is consistent with getting flesh from bones off an animal that was quite dead at the time.

“The bones don’t reveal whether the cannibal was scavenging or was also the killer of the tyrannosaur,” McLain said.

“To our knowledge, this is the first description of tyrannosaur cannibalism in the Lance Formation,” he said. “Tyrannosaur cannibalism has been previously noted in Daspletosaurus in the Dinosaur Park Formation in Alberta, Canada.”

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Matthew A. McLain et al. 2015. Tyrannosaur Cannibalism: A Case of a Tooth-Traced Tyrannosaur Bone in the Lance Formation of Eastern Wyoming. Geological Society of America Abstracts with Programs, vol. 47, no. 7, p. 68