Fearsome Sharks of Today Evolved When Ancient Oceans Got Hot

By Jeanne Timmons | The New York Times |

THE NEW YORK TIMES - It sounds like something out of a Hollywood film script, but it really happened: Shark-evolution researchers say that increased ocean temperatures more than 100 million years ago may have caused sharks to grow bigger, swim faster and become the powerful predators we know today.

In a paper published last month in the journal Current Biology, scientists reported that they measured fin sizes and body lengths of 500 extinct and living sharks and compared that information with data from the evolutionary shark family tree. Their results indicate that when the ocean got very hot approximately 122 million years ago during the Cretaceous period, some sharks abandoned their habitat on the seafloor and moved up into the open ocean. That ascent may have altered their fin and body structure, which led to changes in their size and ability to swim.

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Sharks and other fish are similar to most animals, Timothy Higham, a co-author and professor at the University of California, Riverside, explained, “in that the muscle function is very temperature-dependent.” In other words, he said, “if your muscles warm up, they become better at contracting quickly.”

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