Ferocious meat-eating dinosaurs bit each other on the head during fights over food and territory, sometimes hard enough to kill their competitors just as their prey, according to new research by Canadian paleontologists.
Darren Tanke, a researcher at the Royal Tyrrell Museum of Paleontology in Drumheller, Alberta, found bite marks on nearly one-half of the complete fossil skulls he surveyed from a group of meat-eating dinosaurs, known as theropods.
Mr. Tanke, who is an expert in the painstaking task of preparing fossils for display, began noticing bite marks about 10 years ago when working on a Chinese theropod called Sinraptor dongi, which roamed the earth more than 175 million years ago.
"It had marks on the right side of the face and a whole bunch on the lower jaw," Tanke said. "Some punctured right through the bone. You could see that these marks showed some signs of healing and new bone growth. They looked like bite marks on bone when we saw a predator had been preying on the victim."
Tanke then began looking at other theropod skulls in the collection at the Royal Tyrrell Museum.
In four of the nine complete skulls - which is a large sample size for dinosaur hunters - Tanke and museum director Philip Currie found scratches, gouges, and bites on Tyrannosaurus rex, Gorgosaurus, Albertosaurus, and Daspletosaurus.
"That's an astronomically high number," Tanke said. "It would be like seeing half the people on the street with a head injury."
The bite marks were not anywhere else on the fossilized bones. Since then, Tanke has found similar such marks in theropod skulls at the American Museum of Natural History in New York and the Field Museum in Chicago. Tanke and Currie published their findings in the most recent issue of Gaia, an earth-sciences journal.
Tanke speculates that younger dinosaurs fought for social dominance, territory, or food, just like a modern-day pack of wolves, for example. He doesn't think it was a mating ritual because some of the animals are too young.
"There is something happening to animals in the teenage years. When they reach this size, they leave the group or are cast out and go off into the world to set up their own territory. In travels, they encounter other theropods that don't want them there."
One species of North American theropod, Allosaurus, didn't seem to go in for face biting. Tanke checked more than a dozen skulls of the relatively common hunter, but found no marks. "Maybe they had better ways of communicating differences, or maybe they got along better," Tanke said. "We just don't know."
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