Until about two-and-a-half million years ago, the oceans were home to the enormous Carcharocles megalodon. At an estimated maximum size of 18 metres (60 feet), this shark was one fearsome fish, but despite its fame, surprisingly little is known about its diet – or its extinction. Now, some shark-bitten fossils have shed new light on both mysteries.

If a big shark takes a bite out of you, you can bet it's going to leave a mark. Researchers from Italy, Belgium and Peru have found bite marks on seven-million-year-old Peruvian fossils of seals and small baleen whales – bite marks that match the teeth of C. megalodon! Counter to what you might expect, the chomped animals were fairly small, with body lengths under five metres (16 feet), a lot smaller than the shark itself. It seems the big predator may have had a taste for small prey.

Artist's reconstruction of C. megalodon ready to snack on a small baleen whale. Image: Alberto Gennari

This is a very rare find. "[It] represents one of the few fossil evidences for the feeding ecology of this giant extinct shark," says Alberto Collareta of the Università de Pisa, Italy, lead author on the new study. 

It may be exciting to imagine huge carnivores like C. megalodon hunting massive prey like big whales (or, for fun, airplanes), but being a huge predator doesn't necessarily mean eating huge food. Collareta points out that modern-day great white sharks typically go after prey much smaller than themselves, such as seals and small whales. "It seems unlikely that C. megalodon preyed on a regular basis upon large baleen whales," he adds.

Catalina Pimiento of the University of Zurich, who wasn't part of this study, notes the eating habits of C. megalodon have been difficult to assess. "Most of what we 'know' has been inferred based on the great white shark's diet, and a handful of direct evidence," she says. "That's why this study is a good contribution."

But there's more to this discovery than just what was on the shark's menu. These fossils reveal that C. megalodon may have had a favourite kind of food, and the disappearance of this prey could have played a part in the giant predator's extinction.

About 2.6 million years ago, our planet was going through some major changes. The climate was cooling as the Ice Age began and this was affecting habitats, water circulation and food resources all across the oceans. At this time, many small baleen whales disappeared, while their bigger cousins became more common. It was amidst all of this change that C. megalodon vanished from the fossil record, but it has been a challenge to establish the main cause of its extinction.

"Extinction is a complex subject, especially if many factors (e.g. climate, prey, etc.) are interplaying," says Pimiento. She led a study last year that pointed to ecological changes, rather than temperature, as a more likely culprit for the extinction of C. megalodon, though teasing out which specific changes is tricky.

Collareta and his team suggest food was a factor. The cooling climate and shifting habitats may have led to the disappearance of the small whales that C. megalodon relied upon, which in turn left the shark more vulnerable to the stresses of a changing world. But the full story remains to be uncovered.

"Scientific discussion on this regard is far from being over," Collareta says. "We just hope that our hypotheses will stimulate a debate on this still quite foggy subject." 

The research was partially funded by a grant from the National Geographic Society Committee for Research Exploration.


Top header image: Robert Williams, Flickr