Twenty million years ago, a predator with a mouth like a subway gate and teeth the size of your palm wandered the seas. The megalodon, the largest shark to ever live on Earth, could grow more than 50 feet long, and was the scourge of the ocean for millions of years. Then he disappeared. The megalodon no longer existed.
What exactly happened to push this shark beast to extinction is a topic of great debate among scientists. Now, an article published Tuesday in the journal Nature Communications suggests that great white sharks, which coexisted with the megalodon, preyed on the same types of animals that the much larger shark ate. This evidence helps support the theory that competition with the great white, a predator that is still strong today, could have been a factor that took the megalodon out of the picture. It also highlights the idea that a predator does not have to be the largest to dominate an ecosystem.
Rebuilding the long-standing ocean food chains is a difficult task, said Jeremy McCormack, a geoscientist at the Max Planck Institute for Evolutionary Anthropology in Germany and author of the new article. You can’t see how extinct animals feed or set up a camera to spy on how they lived.
But there are other methods. One option for deducing what an animal ate is to examine the molecules that make up its body. Zinc isotope levels in the teeth of today’s mammals correlate with where they fall in the food chain, many other studies have found: the higher an animal is, the lower the zinc isotope values they show. . Because the teeth fossilize well, the team wondered if the same thing would happen if they looked at their teeth millions of years ago.
Using teeth from more than a hundred sharks, extracted from living and extinct species today, the researchers did tests to see if zinc levels changed as the teeth changed. They also confirmed that in current sharks, zinc isotope values reflect their place in the ecosystem: sharks that eat small fish have higher values, for example, than sharks that eat whales and are higher in the food chain.
Researchers then considered the trophic network drawn by the numbers of old teeth. The results showed intriguing patterns.
“We have the same range of zinc isotope values in the great white sharks, in the same locality, as the megalodon,” Dr. McCormack said. “It’s super interesting. Obviously they have a very different size, but that means they have an overlap in their prey species.”
He paints a picture of the huge shark gliding, casting a shadow like a bus in search of unfortunate fish, and in the background, the big white, a relatively tiny shape at the time, taking the same prey by itself.
If the great white eats the same types of prey, perhaps the smaller sharks competed with the megalodon for food. If so, they could have contributed to its eventual downturn, along with possible 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 try to bring together what ecosystems looked like millions of years ago, who ate whom and where, a measure such as the value of the zinc isotope can help fill in the blanks, he hopes. It’s still a new idea to use it so far back in time, but perhaps with more data from other creatures, it may finally help us understand what happened so long ago, when organisms like the megalodon point to the fossil record.