Shark tooth enamel suggests prehistoric great whites may have competed with giant megalodons for food

• Megalodons were the largest carnivorous sharks ever, four times the size of a great white shark.
• Great whites may have contributed to megalodon's extinction by eating the same prey, a new study suggests.

Megalodon sharks were the prehistoric oceans' largest predators, but that doesn't necessarily mean they were the best hunters.

They are the biggest carnivorous sharks to ever swim the seas. Megalodons grew to roughly 65 feet long, possibly by eating their siblings in the womb — four times the size of a great white shark. Nevertheless, great whites may have been formidable hunting competitors when they patrolled the oceans in the early Pliocene, some 5 million years ago.

Based on an analysis of tooth enamel from nearly two dozen shark species, some contemporary and some long extinct, researchers determined that megalodons and great whites were on the same level of the food chain. That means they likely hunted the same prey in the same oceans. If great white sharks made a big enough dent in the shared food supply, they could have contributed to the megalodon's eventual extinction, about 3 million years ago.

"What organisms eat really dictates how they evolve, and whether they are, quote, unquote, 'winners or losers' in the game of life," Michael Griffiths, a geochemist at William Paterson University, who analyzed shark teeth for the study, told Insider.

"The jury's still out as to what led to the extinction of megalodon. But I think this paves the way to future research in terms of really nailing down what led to their demise," he added.

The shark-tooth study was published in the journal Nature Communications on Tuesday.

Tooth enamel contains hints of ancient creatures' diets

Teeth are some of the best-preserved remnants of ancient sharks, partially thanks to the fluoride in their enamel. That same enamel also preserves hints of the sharks' diets, in the form of certain isotopes of zinc.

Animals and fish tend to concentrate the heavier zinc isotopes in their bones. Because predators mostly eat muscle, not bone, their bodies have lower levels of heavy zinc isotopes, and higher levels of light zinc isotopes, than prey animals do. As you go up the food chain, each new level of predator has less and less of the heavy zinc isotopes.

To figure out how high each shark was on the food chain — or which "trophic level" it occupied — the researchers measured the ratio of heavy versus light zinc isotopes in the teeth. The technique has helped scientists piece together the diets of ancient land animals, but Griffiths said this is the first time it's been used on marine vertebrates.

The teeth of great white sharks and megalodon had similar isotope levels, indicating that they occupied the same spot in the food chain.

"I'll caution that we don't have a whole lot of data," Griffiths said.

However, he added, because sharks are opportunistic feeders — they'll eat whatever they can get — there's "no doubt" there would be some overlap in what great whites and megalodons ate.

"Being such a large animal, [megalodon] maybe only needed a little bit of competition to really have a big impact on its survival," he said.

The teeth revealed some other trends in shark diets, too.

"The general diet of practically every shark group with modern descendants has apparently not changed so much over the last 20 million years," Kenshu Shimada, a paleobiology professor at DePaul University, research associate at the Sternberg Museum in Kansas, and co-author of the new study, told Insider via email. For example, he said, "extinct tiger sharks were 'generalists' feeding on a wide range of food types, just like the modern tiger shark."

The megalodon's smaller ancestor, Otodus chubutensis, had a zinc isotope depletion that was "off the charts," indicating that its trophic level was "beyond anything in the modern ocean," Griffiths said. That could mean that it survived largely by eating other sharks.

"That suggests that there was a point in time where they truly did rule the ocean," he said.