One of the most striking fossils today are the teeth and reconstructed jaws of the megalodon.
The extinct shark’s jaws are large enough for one or two people to stand inside. They are relics of a dominant predator that thrived about 20 to 3.6 million years ago, a species of shark that likely munched on whales and large fish. They got about 50 feet long, which is taller than a city bus.
What caused the downfall of such a commanding creature is an ongoing investigation, but scientists have uncovered a compelling lead. in the Research recently published in the science journal nature communication, Geoscientists and biologists found preserved chemical evidence (in fossilized teeth) that megalodons and great white sharks coexisted as apex predators toward the end of the megalodon’s reign, about 5.3 to 3.6 million years ago.
“They actually seem to have 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 is, they were competitors for prey.
Previous research, such as that by paleontologist Robert Boessenecker, suggested that such competition might involve a Driver of the Megalodon extinction. This new research suggests the two species coexisted in the world’s oceans and ate the same food for 1 to 3 million years, Boessenecker, a research associate in the Department of Geology and Environmental Geosciences at the College of Charleston, told Mashable. Boessenecker was not involved in this latest study. Ultimately, the megalodons were disadvantaged because they likely took longer to grow that large and reach sexual maturity, he said. The great whites would have reproduced faster, outstripping the larger, more energy-intensive Megalodon.
A dominant shark lurks in the deep, dark ocean. Meet the sixgill.
Photo credit: Kenshu Shimada
Importantly, many extinction stories are not straightforward. Climate change may also have been a factor, as global temperatures cooled during a period called the Pliocene, about 5.3 to 2.6 million years ago. Cooler oceans may have made life harder for megalodons. “Because the adult sharks depended on tropical waters, the drop in ocean temperatures likely resulted in significant habitat loss.” explains the Natural History Museum in London. “It may also have caused the megalodon’s prey to either go extinct or have adapted to the cooler waters and moved where the sharks couldn’t follow.”
Many sea creatures, such as mammals, turtles, sharks and seabirds, became extinct during the Pliocene. Perhaps great white sharks, being able to subsist on fewer calories, were better suited to surviving as top predators in a changing world.
Photo Credit: Ethan Miller/Getty Images
The giant megalodon teeth
Fossilized megalodon teeth, which can be the size of a human hand, are scattered and common across the planet. That’s because their jaws were occupied by 276 teeth, and sharks lose (and replace) thousands upon thousands of teeth over the course of their lives. A large number of the megalodon’s hard teeth were eventually 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 is an essential element for organisms, and the different types of zinc isotopes in the teeth of animals reflect the animals’ different positions in the food chain, explained DePaul University’s Shimada. For example, larger sharks that feed on marine mammals have a different zinc composition than smaller sharks that feed on fish or plankton.
Ultimately, in the early Pliocene (about 5 million years ago), megalodons and great white sharks had similar zinc compositions, meaning they likely competed for the same prey.
However, the story of the demise of the megalodon is far from over. But now that researchers have shown for the first time that zinc isotopes are conserved in shark teeth for millions of years, scientists can reveal far more about the diet and life of creatures that lived in Earth’s ancient seas.
“Using zinc isotopes for fossils could revolutionize the way we study the food webs of extinct marine vertebrates, and I’m very excited to see what comes next,” said Boessenecker.