Cannibal dinosaurs resorted to eating each other when food was scarce

Abundant bite marks on a collection bones from the Jurassic Period show that predatory dinosaurs called allosaurs often scavenged on carcasses at one site – including those of other allosaurs.

There is no reason to think that cannibalism was rare among predatory dinosaurs, says Stephanie Drumheller at the University of Tennessee, Knoxville, but we don’t have a lot of evidence for it. Only T. rex and another species called Majungatholus have been shown to be at least occasional cannibals.

Drumheller’s team studied a unique collection of 150-million-year-old fossil bones from the Mygatt-Moore quarry in Colorado. Normally a lot of material gets left behind when a site is excavated. “Only the pretty stuff gets brought back from the field,” she says.

But for one season, Julia McHugh at the Museums of Western Colorado collected every single bone that was found at the quarry, with the help of volunteers. Nearly 30 per cent of the 2368 bones have bite marks on them, far more than thought normal. Usually less than 5 per cent of dinosaur bones have bite marks.

“For dinosaurs, it’s really, really weird,” says Drumheller. “To find 30 per cent was really nuts.”

The team think most of the bite marks were made by allosaurs, which were the most common large predator found at the site. A lot of the bite marks were found on the bones of other allosaurs.

Why scavenging and cannibalism was so common at the site is unclear. One explanation is that something is unusual about this particular site – maybe environmental conditions forced predators to scavenge more.

The other explanation, says Drumheller, is that this bone collection reflects the norm. The tendency of fossil hunters to leave behind damaged bones could have skewed our picture. She is trying to persuade people at other sites to try collecting every single bone, too. But it is a lot of work, especially if the bones are from massive species such as the allosaurs, which could grow up to 10 metres long.

“With an Apatosaurus, every one of those bones can be huge,” says Drumheller.

Journal reference: PLoS ONE, DOI: 10.1371/journal.pone.0233115