2 mar 2013
The finding, detailed in the current issue of the journal Cretaceous Research, also reveals that the healing properties of dinosaur skin were likely very similar to that of modern reptiles.
The lucky dinosaur was an adult Edmontosaurus annectens, a species of duckbill dinosaur that lived in what is today the Hell Creek region of South Dakota about 65 to 67 million years ago.
A teardrop-shaped patch of fossilized skin about 5 by 5 inches (12 by 14 centimeters) that was discovered with the creature's bones and is thought to have come from above its right eye, includes an oval-shaped section that is incongruous with the surrounding skin.
Bruce Rothschild, a professor of medicine at the University of Kansas and Northeast Ohio Medical University, said the first time he laid eyes on it, it was "quite clear" to him that he was looking at an old wound.
"That was unequivocal," said Rothschild, who is a co-author of the new study.
A Terrible Attacker
The skull of the scarred Edmontosaurus also showed signs of trauma, and from the size and shape of the marks on the bone, Rothschild and fellow co-author Robert DePalma, a paleontologist at the Palm Beach Museum of Natural History in Florida, speculate the creature was attacked by a T. rex.
It's likely, though still unproven, that both the skin wound and the skull injury were sustained during the same attack, the scientists say. The wound "was large enough to have been a claw or a tooth," Rothschild said.
Rothschild and DePalma also compared the dinosaur wound to healed wounds on modern reptiles, including iguanas, and found the scar patterns to be nearly identical.
It isn't surprising that the wounds would be similar, said paleontologist David Burnham of the University of Kansas Biodiversity Institute, since dinosaurs and lizards are distant cousins.
"That's kind of what we would expect," said Burnham, who was not involved in the study. "It's what makes evolution work—that we can depend on this."
Dog-Eat-Dog
Phil Bell, a paleontologist with the Pipestone Creek Dinosaur Initiative in Canada who also was not involved in the research, called the Edmontosaurus fossil "a really nicely preserved animal with a very obvious scar."
He's not convinced, however, that it was caused by a predator attack. The size of the scar is relatively small, Bell said, and would also be consistent with the skin being pierced in some other accident such as a fall.
"But certainly the marks that you see on the skull, those are [more consistent] with Tyrannosaur-bitten bones," he added.
Prior to the discovery, scientists knew of one other case of a dinosaur wound. But in that instance, it was an unhealed wound that scientists think was inflicted by scavengers after the creature was already dead.
It's very likely that this particular Edmontosaurus wasn't the only dinosaur to sport scars, whether from battle wounds or accidents, Bell added.
"I would imagine just about every dinosaur walking around had similar scars," he said.
"Tigers and lions have scarred noses, and great white sharks have got dings on their noses and nips taken out of their fins. It's a dog-eat-dog world out there, and [Edmontosaurus was] unfortunately in the line of fire from some pretty big and nasty predators ... This one was just lucky to get away."
Mysterious Escape
Just how Edmontosaurus survived a T. rex attack is still unclear. "Escape from a T. rex is something that we wouldn't think would happen," Burnham said.
Duckbill dinosaurs, also known as Hadrosaurs, were not without defenses. Edmontosaurus, for example, grew up to 30 feet (9 meters) in length, and could swipe its hefty tail or kick its legs to fell predators.
Furthermore, they were fast. "Hadrosaurs like Edmontosaurus had very powerful [running] muscles, which would have made them difficult to catch once they'd taken flight," Bell said.
Duckbills were also herd animals, so maybe this one escaped with help from neighbors. Or perhaps the T. rex that attacked it was young. "There's something surrounding this case that we don't know yet," Burnham said.
Figuring out the details of the story is part of what makes paleontology exciting, he added. "We construct past lives. We can go back into a day in the life of this animal and talk about an attack and [about] it getting away. That's pretty cool."
