Whales don’t swim like fish do. Instead of moving their tales side-to-side like a shark or a sunfish, the marine mammals pump their tails up-and-down to propel themselves forward. But over 50 million years ago, the earliest whales had legs and could walk on land. Adapting to life in the sea required a new way of moving, and a fossil uncovered in Egypt helps estimate the time when whales became primarily tail-powered swimmers.
The partial skeleton, described today by University of Michigan paleontologist Iyad Zalmout and colleagues in PLOS ONE, is an ancient whale that swam the seas of what’s now Egypt around 39 million years ago. The fossil was found in the desert of Wadi Al-Hitan, a place so rich in cetacean fossils that it’s known as Whale Valley.

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