The megatooth shark Otodus megalodon was an absolute unit, estimated to have been around 15 meters (50 feet) long with fins the size of people (though we don’t know for absolute certain what they looked like). It’s difficult, then, to imagine these enormous apex predators being outcompeted – but new research suggests that great white sharks might have had something to do with O. megalodon shuffling out of existence.

Sharks’ teeth, as well as being great for slicing prey up, carry enormous scientific value. Previous research has used teeth and comparative anatomy to estimate the size of extinct marine animals. Now, a new paper published in Nature Communications has looked at the enamel of megalodon teeth to learn more about what they were eating when they were alive.

When sharks are cooking up new teeth (they never run out), their diet can influence how much zinc is incorporated into the enamel. By working backwards, scientists can use zinc isotope values to establish what the toothy owners’ diets were like as well as establish their footing in the food chain.

“Here, we demonstrate, for the first time, that diet-related zinc isotope signatures are preserved in the highly mineralised enameloid crown of fossil shark teeth,” said Thomas Tütken, professor at the Johannes Gutenberg University’s Institute of Geosciences, in a statement.

O. megalodon’s teeth were analyzed in this way, alongside 13 fossilized specimens plus the teeth of 20 shark species still alive today. The resulting database demonstrated that zinc was indeed a window into an animal’s trophic past, revealing insights into sharks’ diets as far as 23 million years ago when O. megalodon reigned supreme.

A comparison of great whites (Carcharodon carcharias) and megalodons – two species that once coexisted during the Early Pliocene – showed that the two sat side-by-side in the food chain. This likely indicates that they were after the same prey, such as whales, and so were competing for the same resources.

The largely overlapping trophic levels between megalodons and great whites are “truly remarkable,” says Michael Griffiths, professor at the William Paterson University, when you take into consideration the animals’ sizes. O. megalodon reached around 15 to 20 meters (49 to 66 feet) in size, while our diddy little (in megatooth terms) great white would’ve been at most six meters (19 feet).

The exact cause of megalodon’s extinction isn’t yet known for certain, and while a few ideas have been floated in the past the authors of this new paper suggest that it was likely the result of a multitude of factors including climate and environmental changes. However, they also demonstrate for the first time that the competition posed by great whites – despite their comparatively smaller size – could well have been another nail in the megalodon’s coffin.

The study authors’ conclusion represents a curious crossover in the history of two of Earth’s greatest predators, but it also promotes a novel approach for studying diet that could have applications outside of shark ecology.

“Our research illustrates the feasibility of using zinc isotopes to investigate the diet and trophic ecology of extinct animals over millions of years, a method that can also be applied to other groups of fossil animals including our own ancestors,” concluded lead author Jeremy McCormack, a researcher at the Max Planck Institute for Evolutionary Anthropology and the Goethe-University Frankfurt, in a statement.