Pic: Amazing four-legged fossil shows how walking whales learned to swim Read more: https://www.newscientist.com/article/2198740-amazing-four-legged-fossil-shows-how-walking-whales-learned-to-swim/#ixzz6Brimj95W

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Whales used to walk on land

A. Gennari

A fossil of a 43-million-year-old whale that was still able to walk on land on four legs has been found in Peru. It is the first amphibious whale found in the southern hemisphere, and suggests that whales managed to swim across the South Atlantic early in their evolution.

The 3-metre-long animal looked a bit like an otter or a beaver, with four legs and a large tail for swimming.

“It was still capable of bearing its weight on its limbs,” says Olivier Lambert at the Royal Belgian Institute of Natural Sciences, a member of the team that made the discovery. “It was intermediate between fully walking and fully aquatic.”

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Whales started evolving in South Asia around 50 million years ago, from a dog-like creature related to deer and hippos. As they became more aquatic, these early whales began spreading along coasts.

Fossils of semi-aquatic whales have recently been found in West Africa. The latest discovery suggests that these early whales managed to swim from there to South America at least 43 million years ago.

Read more: Gallery: Whale evolution – from land to sea

At the time, the West African coast was just 1200 kilometres from what is now Brazil, and there was a westward current. But it would still have taken a week or two to make the crossing. That may suggest that these whales were already capable of surviving without fresh water, and of sleeping at sea.

They soon reached North America too, where fossil teeth dating to around 41 million years ago have been found.

The last common ancestor of all modern whales and dolphins lived 37 million years ago, so the new discovery may be one of the ancestors of modern whales. However, it is far more likely to be a cousin – a member of a side branch that died off, says Lambert.

Source: https://www.newscientist.com/article/2198740-amazing-four-legged-fossil-shows-how-walking-whales-learned-to-swim/