Great white sharks may have driven megalodon to extinction
Megalodon (Otodus megalodon), one of the largest sharks to have ever lived, mysteriously vanished from the fossil record about 3.6 million years ago. Now scientists suspect that the massive predator may have been driven to extinction by a rival marine species: great white sharks. Prior research hypothesised that megalodon’s decline may have coincided with the rise of great white sharks (Carcharodon carcharias), which likely hunted the same prey as their larger cousin.
The megalodon’s relatively sudden disappearance has been evidenced from bite marks on the bones of other marine animals; these scars were made by both great whites and megalodon, suggesting that the two species may have competed for food resources. But these bite marks provided only a single snapshot of isolated interactions between predator and prey. To find out if great white sharks truly starved megalodon out of existence would require a more complete survey of both species’ diets.
For that, Jeremy Mccormack, a geoscientist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and his colleagues looked for clues in the animals’ teeth; they looked not at tooth size or shape, but rather at the amount of zinc that was present in each tooth. “Zinc is essential for organisms, as it plays an important role in a wide range of biological processes,” Mccormack said. Importantly, zinc is incorporated into teeth as they grow. When a predator hunts, it ingests minerals and nutrients from its prey. One of those is zinc, which comes in two isotopes – variations of the same element with a different number of neutrons. One zinc isotope is heavier. If teeth contain more of the lighter isotope and less of the heavier isotope, the animal is closer to the top of the food chain in its ecosystem. But if the teeth hold more of the heavier isotope, chances are that the animal is a bottom-feeder. These zinc ratios enable scientists to determine an ancient animal’s trophic position with a great deal of accuracy.
Researchers examined teeth from 20 modern species of fish, including sharks from wild and aquarium populations, and compared the zinc ratios in the teeth of the living fish with those in teeth from ancient great whites and extinct megalodon. Great white sharks evolved about 4 million years ago, overlapping with megalodon for approximately 400,000 years. At first, megalodon and great whites occupied separate niches and didn’t compete with one another.
But the scientists discovered that zinc ratios in fossil shark teeth documented a shift in that relationship – one that caused them to directly bump fins with one another. About 5.3 million years ago, some populations of great whites began to shift their position up on the food chain to become top predators themselves, invading megalodon’s territory.