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Fossil records show that roughly 90 percent of the planet's open-ocean sharks inexplicably vanished.


Sharks are some of nature’s greatest survivors. For more than 400 million years, the marine predators have plied Earth’s waters, from shallow reefs to the heart of the open ocean. Sharks are older than the oldest fossil forest. They’ve made it through at least four mass extinctions.

And yet, 19 million years ago, something mysteriously dealt open-ocean sharks a huge blow—one from which they’ve never recovered.

Records of this extinction, detailed for the first time in the journal Science, come in the form of shark scales, called denticles, found in seafloor samples from the Pacific Ocean. Based on the shapes and abundance of denticles in the samples, the researchers estimate that the planet’s open-ocean shark populations suddenly and inexplicably fell by more than 90 percent. By contrast, during the extinction event that killed off the non-avian dinosaurs 66 million years ago, sharks suffered losses of roughly 30 percent.

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Most Uber drivers need a smartphone to get to their destinations. But sharks, it seems, need nothing more than their own bodies—and Earth’s magnetic field. A new study suggests some sharks can read Earth’s field like a map and use it to navigate the open seas. The result adds sharks to the long list of animals—including birds, sea turtles, and lobsters—that navigate with a mysterious magnetic sense.

“It’s great that they’ve finally done this magnetic field study on sharks,” says Michael Winklhofer, a biophysicist at the Carl von Ossietzky University of Oldenburg in Germany, who was not involved in the study.

In 2005, scientists reported that a great white shark swam from South Africa to Australia and back again in nearly a straight line—a feat that led some scientists to propose the animals relied on a magnetic sense to steer themselves. And since at least the 1970s, researchers have suspected that the elasmobranchs—a group of fish containing sharks, rays, skates, and sawfish—can detect magnetic fields. But no one had shown that sharks use the fields to locate themselves or navigate, partly because the animals aren’t so easy to work with, Winklhofer says. “It’s one thing if you have a small lobster, or a baby sea turtle, but when you work with sharks, you have to upscale everything.”

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