Twenty million years ago, a predator with a mouth like a subway door and teeth the size of your palm roamed the seas. Megalodon, the largest shark to ever live on Earth, could grow to over 50 feet in length, and it was the scourge of the ocean for millions of years. Then he disappeared. The megalodon was no more.
What exactly happened to drive this beast of a shark to extinction is the subject of much debate among scientists. Now, a paper published Tuesday in the journal Nature Communications suggests that the great white sharks, which coexisted with the megalodon, fed on the same types of animals the much larger shark ate. This evidence helps support the theory that competition with the great white, a predator that is still going strong today, may have been one of the factors that brought the megalodon out of the picture. It also highlights the idea that a predator doesn’t need to be the biggest to ultimately dominate an ecosystem.
Reconstructing ocean food chains from long ago is a difficult task, said Jeremy McCormack, a geoscientist at the Max Planck Institute for Evolutionary Anthropology in Germany and author of the new paper. You can’t watch extinct animals feed or set up a camera to spy on how they lived.
But there are other methods. One option for inferring what an animal has eaten is to examine the molecules that make up its body. The levels of zinc isotopes in the teeth of living mammals correlate with their position in the food chain, according to many other studies: the higher an animal is in the food chain, the higher the zinc isotope values it displays are low. Because teeth fossilize well, the team wondered if the same would be true if they were looking at teeth from millions of years ago.
Using the teeth of more than a hundred sharks, drawing from species alive today and long gone, the researchers ran tests to see if zinc levels changed as the teeth aged. They also confirmed that in living sharks, zinc isotope values reflect their place in the ecosystem – sharks that eat tiny fish have higher values, for example, than sharks that eat whales and are more high in the food chain.
The researchers then looked at the food web sketched by the digits of the ancient teeth. The results showed intriguing patterns.
“We have the same range of zinc isotope values in great white sharks, in the same locality, as megalodon,” Dr McCormack said. “It’s very interesting. They are obviously very different in size, but that implies they have an overlap in their prey species.
He paints a picture of the massive shark gliding, casting a shadow like a bus in its pursuit of hapless fish, and in the background the great white, a relatively small form at the time, snatching the same prey for him. -same.
If the great white ate the same types of prey, then perhaps the smaller sharks were competing with the megalodon for food. If so, they may have contributed to its eventual downfall, alongside potential changes in other aspects of the ecosystem, such as climate. It’s an idea that scientists have floated in the past, but there was no geochemical evidence to support the hypothesis, Dr McCormack said.
As researchers seek to piece together what ecosystems looked like millions of years ago — who ate who and where — a measure like the isotopic value of zinc can help fill in the gaps, he hopes. It’s still a new idea to use it this far back in time, but maybe with more data from other creatures it could eventually help us understand what happened so long ago , when organisms like megalodon disappear into the fossil record.