However, it's an open question whether the offender killed or was just scavenging for a meal when it gnawed on the fallen tyrannosaur, the researchers said.
As they continue to study the masticated fossil, the researchers plan to invest more time analyzing the serration marks. Earlier studies on serrated Komodo dragon teeth show a relationship between serration size and the animal's size. Other studies have used this technique on tyrannosaurs, and McLain said it will likely work in this case, too.
"Exactly who did the eating that day, in the Late Cretaceous, could still be sorted out by the same grooves," he said. "It only works if you know what species it is. And since Tyrannosauruses are the only large predators in these formations, it's pretty straightforward."
But that might be jumping to conclusions, said Thomas Carr, an associate professor of biology at Carthage College in Wisconsin and a vertebrate paleontologist, who was not involved in the study.
It's not clear from the unpublished findings, thus far, if the bone belongs to T. rex, or simply another theropod, Carr said. (Theropods, like birds, have hollow bones, but more direct evidence is needed to identify it as a T. rex, he said.)
Moreover, it's not uncommon to find tooth marks scarring tyrannosaur bones, Carr said. But most researchers don't document the events, largely because the marks don't teach researchers much about the biology of the organism, he said. Some work has examined multiple tooth-marked bones to see whether there are any common patterns - and thus, a common strategy - that tyrannosaurs used for dismembering a carcass. Perhaps the new finding will contribute to this approach, Carr said.
"It shouldn't be a surprise to us that a top predator would eat anything available to it, since the environment is not banquet," Carr told Live Science. "But we know that this sort of behavior, cannibalism, may occur across the board for theropods, if not for most vertebrates."
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