Analysis of the battle-scarred skull of a large tyrannosaur found in Alberta suggests the carnivores fought each other viciously in life and snacked on each other after death.
That conclusion was drawn by David Hone, a lecturer in ecology at the Queen Mary University of London, who analyzed the skull and lower jaw of a Daspletosaurus found in Alberta and reported his findings in a recent study.
The Daspletosaurus, a slightly smaller cousin of a Tyrannosaurus rex, was just under six metres long and weighed about 500 kilograms when it died.
Hone's analysis of the bones found the skull and jaw were both raked with bite marks, some of which showed evidence of healing — indicating they were made when the animal was still alive — and others that were made after the dinosaur died.
"And actually we've got good reason to think this occurred quite a long time after it died — days if not actually weeks," Hone said.
And Hone said he has compelling reasons to think the bite marks were made by another tyrannosaur, rather than some other type of predator.
First, tyrannosaurs had unique teeth that were not only ideal for crunching through bones, but also left distinctive marking patterns, he said.
Also, like most large predators where tyrannosaurs lived, they were very likely the only large carnivores in the area
"If you got out to somewhere like the Maasai Mara (in Kenya), you will see hundreds of wildebeests and zebra and giraffe for every lion that you come across," he said. "There is not going to be space for one every mile or so in the ecosystem."
"So when you see big marks and bigs chunks of bone effectively are being broken and scored and scraped through, it's hard to mistake it for anything else."
The bigger picture
While researchers have previously suggested tyrannosaurs — like other large carnivores — once fought and scavenged amongst themselves, this most recent find helps solidify those claims.
The palaeontologists with the Royal Tyrrell Museum in southern Alberta who excavated the skull did an exceptional job collecting not only the bones, but recording their relationship to one another as well as to their geographical context, said Hone.
"That allowed us to put back together this picture and work out the chain of events that had occurred."
The problem, Hone said, is that dinosaur skeletons are incredibly rare finds — meaning that there is often only a single record of a certain type of event or behaviour.
"You just don't know — is that a complete one-off that we've been lucky enough to find, or was that naturally a relatively regular occurrence and we just don't see it very much because bones are fundamentally rare?" he said.
"Even in a place like Alberta, where there are tons and tons of dinosaur bones, actual records like this are still very, very few and far between."
And because tyrannosaurs themselves were also likely few and far between, with large territories where meeting others of their species was relatively unlikely, finding fossil evidence of in-fighting is even more unlikely.
Given those odds, finding evidence at several sites that the animals were fighting and feeding on each other is "all the more intriguing," Hone said.
"Maybe the tyrannosaurs were doing something a little bit different" than other carnivorous dinosaurs of the age, he said.
"It's a real delight to find this."