Humans do it, big cats do it, even grasshoppers do it, but for the first time, paleobiologists have found solid evidence of dinosaurs eating their own kind.
The new evidence comes from fossilized bones of a large bipedal dinosaur, Majungatholus atopus, that were discovered in 160-million-year-old rocks in an ancient river valley in Madagascar. Flash floods may have buried the carcasses quickly, preserving extraordinary details in the skeleton. "The bones are incredible," says Kristina Curry Rogers, a paleontologist at the Science Museum of Minnesota in St. Paul, and co-author of a report describing the find in the 3 April issue of Nature.
Finely serrated gouges on some M. atopus leg bones can be seen with the naked eye, says Curry Rogers. She and co-workers Raymond Rogers of Macalester College in St. Paul and David Krause of the State University of New York, Stony Brook, tried to match the wounds with fossil teeth found in the same area. They ruled out two large crocodiles because their teeth erupt in an irregular pattern, unlike the teeth marks on the M. atopus bones. A smaller dinosaur, Masiakasaurus knopfleri, has a jaw that could make a similar pattern, but is much too small. Only the jaws of M. atopus matched the size of both the gouges and the serrations.
Cannibalism is a common response for animals in difficult environments, says Rogers. And Madagascar was no picnic for dinosaurs: Ancient soils and other evidence show that the island, which was much closer to the equator than it is today, probably was arid desert. Rogers says he also found scoop-shaped burrows from carrion beetles in the dinosaur bones. Observations of modern carrion beetles show they prefer flesh for their pupating cavities but can dig into bone in very dry conditions.
"This [is] definitely the best evidence ever of cannibalism" by dinosaurs, says Gregory Erickson of Florida State University in Tallahassee. Other suspected cases, in tyrannosaurs and Coelophysis bauri, have been unconvincing, he says. It's not clear whether M. atopus killed its kin or just snacked on them after death. The authors "can't demonstrate definitively one way or the other that this is a case of scavenging versus hunting--they look identical," says Thomas Holtz of the University of Maryland, College Park.