Cannibals are creatures which eat their own kind.
Old bones that have been dug up on the island of Madagascar have teeth marks in them that could only have come from another similar dinosaur.
This shows that dinosaurs chomped on their own kind when food became really short.
Giant meat-eater
The bones come from a ferocious dinosaur called Majungatholus atopus, which lived 65-70 million years ago.
There were huge food and water shortages around this time and scientists think they turned to cannibalism to survive.
Experts thought some dinosaurs may have been cannibals but there's not been any proof before now.
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