Shark Teeth Found Stuck in Ancient Ammonite Shell

A shelled fossil discovered in an amateur’s collection may harbor the first direct evidence of prehistoric sharks eating ammonites some 150 million years ago.

The palm-sized ammonite, an extinct marine animal and distant relative of the modern nautilus, was fossilized with three shark teeth stuck in its shell, plus holes from the bite. Shark bite marks have been found in other fossils, such as crocodile poop, but with tough-shelled ammonites, paleontologists couldn’t pinpoint sharks and rule out other fishes or marine reptiles.

It’s not often one knows with extreme certainty what 150-million-year-old predators actually ate.

“For the first time we have a direct link between the predator and prey. We can even give a name to the predator, which is a hybodont shark called Planohybodus,” said paleontologist Romain Vullo of Université de Rennes and author of the study published March 31 in Naturwissenschaften.

Hybodont sharks, also named hump-toothed sharks, grew to nearly 7 feet long and roamed ancient oceans for about 200 million years before vanishing with the dinosaurs 65 million years ago. Ammonites floated in the oceans at the same time, growing anywhere from a couple of inches to 10 feet wide. Soft tissue inside their shells was an attractive food source to many creatures.

Some species of hybodont sharks had flat teeth able to crush ammonites and other shelled creatures, but most species were thought to dine exclusively on fish.

“Before this discovery, we thought Planohybodus ate only fish because of its sharp teeth. They seemed better-suited for that kind of predation,” Vullo said. “This specimen shows it probably had a much larger range of prey, including ammonites.”

After reading reports of shark-like bite marks in ammonite fossils, Vullo remembered seeing the fossil in an acquaintance’s collection and asked to study it. He was able to match the teeth — one still embedded, two removed by the collector — to Planohybodus.

Vullo thinks such sharp teeth maimed ammonites by poking holes in their shells’ air chambers, which the creatures used for stabilization and steering. Once an ammonite lost control, a shark could conveniently crush it.

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