Tyrannosaurus rex craved meat so much that it ate individuals from its own species, according to new research supporting that this 35-foot-long carnivorous dinosaur from the Cretaceous Period was a cannibal.
Only one other dinosaur, Majungatholus, is known to have engaged in similar behavior, but paleontologists now believe Gorgosaurus (another huge meat-eater) and many other gigantic predatory dinosaurs were also cannibals.
"A lot of large carnivores tend to be cannibals -- lions, hyenas, alligators, polar bears," researcher Nicholas Longrich told Discovery News. "They're equipped to kill and eat large animals, and if you're hungry enough, fellow members of their species are just one more kind of large animal."
"Of course, small, cute, furry animals like ground squirrels are also highly cannibalistic," added Longrich, who is a paleontologist at Yale University.
He and his colleagues made the discovery, published in the latest PLoS ONE journal, while searching through western North American dinosaur fossil collections. Longrich discovered a T. rex fossil with large tooth gouges in it.
"The tooth marks are typical of tyrannosaur tooth marks, and are just too big to come from any other carnivorous dinosaur," he said, adding that T. rex teeth were about 8 inches long.
Further supporting the attribution is the fact that T. rex is known to have been the only big carnivore in western North America 65 million years ago.
When Longrich searched through additional T. rex fossil collections from several different museums, he found other evidence that this dinosaur was a cannibal. Three foot bone fossils, including two toes, and one arm fossil all retained big tooth marks due to feeding.
While it's possible that all or some of the gouges were the result of scavenging, Longrich and his colleagues think it's likely that the dino-on-dino feasting happened after fights, a meal that would help the cannibal victor.
"You're killing a competitor and getting a free meal at the same time," he explained. "The hunting is going to be better if you eat the other hunters."
Battles between these mega carnivores must have been quite a spectacle.
"If I was a tyrannosaur facing another tyrannosaur face-to-face, I'd say the only real strategy is to wait for an opening and then go straight for the head," he said. "You'd want to clamp down on your opponent's neck or jaws to prevent it from fighting back. If you attack any other part of the body, then you're left open to counterattack."
This suspected fighting behavior, the cannibalism finding and the massive size of these dinosaurs all indicate T. rex was a solitary predator that did not hunt in packs. Some large modern carnivores, such as lions and hyenas, do hunt in organized groups, but T. rex individuals likely acted on their own.
"Personally, I suspect that a whole pack of full-grown T. rex would have a very hard time finding enough to eat," Longrich said.
Thomas Holtz, director of the Earth, Life and Time Program at the University of Maryland, told Discovery News he thinks the new finds are "very compelling."
"There have been face bite marks from tyrannosaurs before, but those were most likely from squabbling, not feeding," Holtz said. "These could only have been made after the dinosaur was dead."
Holtz was not surprised by the discovery, since T. rex was "an enormous animal, and so (it) made a great big corpse."
"No carnivore worth its salt would pass up that kind of a meal," he added.