Monday, September 20th 2021, 2:35 pm - 202 fossils bearing 324 scars create picture of who was fighting — and why.
Illustration shows how Tyrannosaurus rex would fight each other either for territory or to attract mates. (Illustration by Julius Csotonyi)
Whether it was establishing their territory or getting in good with the ladies, male tyrannosaurs got right up in each other's faces during prehistoric clashes of epic proportions.
At least, that's a hypothesis being put forward by a team of Alberta paleontologists that studied 202 tyrannosaurid skull specimens featuring 324 bite marks and battle scars.
"Basically these animals were biting each other on the face," said Caleb Brown, co-author of a recent study and a curator at the Royal Tyrrell Museum in Drumheller, Alta.
That, in itself, isn't unheard of, Brown told CBC's Edmonton AM on Thursday. But the huge number of specimens both confirmed this theory and allowed certain patterns to emerge, such as the significant absence of scars on the smallest tyrannosaurs.
Visit our Complete Guide to Fall 2021 for an in-depth look at the Fall Forecast, tips to plan for it and much more!
"The babies and the juveniles had no bite marks," he said.
"We're thinking that one hypothesis that explains this is that they didn't start doing this behaviour until they reached sexual maturity. So they were competing with rivals or trying to impress members of the opposite sex.
The study, published Sept. 6 in the journal Paleobiology, noted that the position and orientation of the facial scars was consistent across tyrannosaurid species, which suggested that the bites were inflicted in repeated conflicts — "likely posturing and sizing each other up, then trying to grab each other's heads between their jaws," Brown explained in an email.
The study also noted that scars appeared on about 60 per cent of the adult-sized skull specimens.
Brown said paleontologists have not yet found a way to tell the sex of a dinosaur, information that would help inform the hypothesis.
Caleb Brown, co-author of the study, is a curator of dinosaur systematics and evolution at the Royal Tyrrell Museum in Drumheller, Alta. (Royal Tyrrell Museum of Palaeontology)
"The interesting aspect of this research is that when you look at modern animals that kind of fight with each other and leave scars on each other, that's dominated by males. So this might be a way of inferring the sex," he said.
Brown believes this type of intrasexual selective behaviour was true for other theropod dinosaurs — those with hollow bones and three-toed limbs.
Some modern-day creatures, like crocodiles, are known to attack each other by biting the face either for territory or access to mates, he said. In contrast, today's birds — which trace their origins to theropods — have evolved away from fighting as a way to establish dominance to putting on spectacular visual or vocal displays.
"It might be that origin of that behaviour that we see so much today, of colourful and really noisy birds today."
Brown said the study began with the discovery of an upper jaw bone with scars in 2017 at the Dinosaur Provincial Park in Drumheller. From this new specimen, he began "documenting the occurrence and morphology of these healed tooth marks."
"I noticed some interesting patterns early on and realized that I was maybe able to say something about the behaviour being preserved," he said by email.
Museum visitors can see some of the fossilized bite marks — including the 2017 specimen — in the Fossils in Focus exhibit, which highlights specimens from its research collection.