Teeth marks found on the bones of dinosaurs have confirmed that some of them were cannibals.
Scientists believe the marks on fossilised bones are the first clear evidence for cannibalism among dinosaurs. No other carnivore alive at the time could have left similar teeth marks, said Raymond Rogers, a geologist from Macalester College in St Paul, Minnesota.
"We have examined literally thousands of dinosaur bones from sites around the world and we've never seen fossil material quite like this," Dr Rogers said.
The bones came from a therapod (meat-eating) dinosaur called Majungatholus atopus, which grew up to 30 feet long and lived on the marshy plains of what is now Madagascar.
Bones from two Majungatholus individuals were analysed by Dr Rogers, David Krause of the State University of New York and Kristina Curry Rogers of the Science Museum of Minnesota.
Their study, published in the journal Science, found that the distinctive sets of tooth marks left on the bones precisely matched the size and spacing of teeth in the jaws of Majungatholus. Smaller grooves in the bones also matched the sharp serrations on the dinosaur's blade-like teeth.
"We examined the jaws and teeth of other known meat-eaters in the Malagasy fauna, including a much smaller carnivorous dinosaur and two large crocodiles," Dr Rogers said. None matched the description.
"We have the smoking gun in the form of diagnostic tooth marks and we can definitely rule out all of the other carnivores known to have been on the scene. These tooth-marked bones are a 'snapshot' of a day in the life and death of Majungatholus," he added.
"Cannibalism as a feeding strategy is very common in the animal kingdom today," said Dr Rogers. It is often carried out in times of extreme hardship. It is not known whether Majungatholus merely scavenged on its dead cousins or actively hunted smaller members of its own species.
"It appears that Majungatholus atopus exploited all available resources during stressful episodes," Dr Rogers said.