Tyrannosaurs Were Fighters And Cannibals

More evidence that members of the tyrannosaur family fought and ate each other.

This painting by Tuomas Koivurinne is an artistic rendering of one Daspletosaurus feeding on another.

Charles Q. Choi, Contributor

(Inside Science) -- What may be the first case of a tyrannosaur fossil damaged by both fighting and cannibalism has now been discovered, scientists say.

Tyrannosaurs, the "tyrant lizards," were a family of dinosaurs that included some of the largest predators to ever walk on land, including the legendary Tyrannosaurus rex. Numerous dinosaur fossils bear signs of damage from tyrannosaurs that was inflicted either in life from combat or in death from scavenging.

However, past studies found that tyrannosaurs not only injured other dinosaurs, but also members of their own species. For instance, gouges have been seen on T. rex bones that could only have been made by another T. rex.

In this latest example of tyrannosaur violence, scientists investigated a roughly 75-million-year-old tyrannosaur skull and jaw discovered in 1994 in Dinosaur Provincial Park in Alberta, Canada. These fossils belonged to a dinosaur genus known as Daspletosaurus, which means "frightful lizard" in Greek. This predator reached up to nearly 30 feet (9 meters) long and 2 tons in weight.

"They didn't have quite the giant heads of Tyrannosaurus, but would have had a 1-meter (3-foot) skull and maybe 10-centimeter-long (4-inch) teeth for the largest," said researcher David Hone, a paleontologist at Queen Mary University of London.

The fossils belonged to a juvenile Daspletosaurus with a head about 21 inches (55 centimeters) long with 2.3-inch-long (6-centimeter) teeth. Prior research suggested this young carnivore was about 10 years old, already reaching 19 feet (5.8 meters) in length and nearly 1,100 lbs. (500 kilograms) in weight.

The researchers found numerous scars on the skull and jaw. These signs of healing were seen with the vast majority of these injuries, indicating that this damage was inflicted when this tyrannosaur was alive. In addition, the scientists found bite marks on the jaw that apparently happened after death.

"The most significant aspect of this work is the demonstration of the ability to infer which wounds occurred in life, and which after death," said vertebrate paleontologist Thomas Holtz at University of Maryland, College Park, who did not take part in this research. "That can help us better understand the pretty rough life of the young Daspletosaurus, as well as document evidence of scavenging."

One puncture wound at the back of the skull was especially large.

"That snapped off some of the bone, yet there were no really obvious ill effects as a result, though it can't have been a good thing," Hone said. "This animal had something of a hard life even though it wasn't an adult. We think of big fights being things for big old warhorses, but clearly younger ones were getting into scraps as well."

Based on the size, form and scale of the injuries this dinosaur sustained when alive, the researchers suggest that at least some of these were inflicted by large theropods, or carnivorous dinosaurs. The most obvious culprits are other tyrannosaurs, since these are the only large theropods known from this area when this Daspletosaurus lived. This in turn suggests this reptile might have regularly fought other members of its own species or other tyrannosaur species.

The investigators suggest the bite marks on the fossilized jaw inflicted after death were from scavenging from another tyrannosaur, either Daspletosaurus or another genus known as Gorgosaurus, which was more common in this area at this time.

"Unfortunately they are extremely similar in size and build -- think jaguar and leopard, say -- so telling them apart is going to be all but impossible when it comes to the postmortem bite," Hone said.

"This study shows that very detailed work can document a whole range of different events that happened to a single individual," Holtz said. "In a way, this is like classic Sherlock Holmes stories, when someone walks into a room and Holmes, by looking at wear and stains on their clothing and shoes and the like, is able to deduce where that person has been and what they had been doing."

Hone and his colleague Darren Tanke detailed their findings online April 9 in the journal PeerJ. The research was crowdfunded through Experiment.com -- nearly $3,000 was raised from more than 50 donors that covered flights, accommodation, and publishing costs, Hone said.