One of the most striking fossils around today are the teeth and reconstructed jaws of the megalodon.
The jaws of the extinct shark are so big, one or two people can stand inside them. They’re relics of a dominant predator that thrived some 20 million to 3.6 million years ago, a shark species that likely munched on whales and big fish. They grew around 50 feet long, which is bigger than a city bus.
What caused the demise of such a commanding creature is an ongoing investigation, but scientists have discovered a compelling clue. In
“They seem to have indeed occupied the same position in the food chain,” Kenshu Shimada, one of the study’s authors and a paleobiologist at DePaul University, told Mashable.
That means they were competitors for prey.
Previous research, like that published by paleontologist Robert Boessenecker, proposed that such competition was a
Credit: Kenshu Shimada
Importantly, many extinction stories aren’t simple. The changing climate could have been a factor, too, as global temperatures cooled during a period called the Pliocene, some 5.3 to 2.6 million years ago. Cooler oceans may have made life harder for megalodons. “As the adult sharks were dependent on tropical waters, the drop in ocean temperatures likely resulted in a significant loss of habitat,”
Many marine creatures, like mammals, turtles, sharks, and seabirds,
Credit: Ethan Miller / Getty Images
The giant megalodon teeth
Fossilized megalodon teeth, which can be the size of a human hand, are scattered around the planet and commonly found. That’s because their jaws were lined with 276 teeth, and sharks lose (and replace) thousands and thousands of teeth during their lives. A good number of the megalodon’s hard teeth, then, were ultimately fossilized.
To determine what both great white sharks and megalodons ate millions of years ago, researchers analyzed the element zinc (specifically a zinc isotope, which is a type of zinc atom) in their respective fossilized teeth. Zinc is a valuable indicator because it’s an essential element for organisms, and the different types of zinc isotopes in animals’ teeth reveal animals’ different positions in the food chain, DePaul University’s Shimada explained. For example, bigger sharks that feed on marine mammals have different zinc compositions than smaller sharks that eat fish or plankton.
Ultimately, megalodons and great white sharks shared similar zinc compositions in the early Pliocene (some 5 million years ago), meaning they were likely competing for the same prey.
The story of the megalodon’s demise, however, is not nearly over. But now that researchers have shown — for the first time — that zinc isotopes are preserved in shark teeth for millions of years, scientists can reveal far more about the diets and lives of creatures who dwelled in Earth’s ancient seas.
“The use of zinc isotopes for fossils could very well revolutionize how we study the food webs of extinct marine vertebrates, and I am very excited to see what comes next,” said Boessenecker.