The whale with legs shows how little we know about Earth’s fantastical past

‘The prehistoric swimmer wouldn’t have looked like any whale we’re familiar with today.’ Photograph: Reuters
The excavation of the extraordinary fossil Peregocetus pacificus in Peru is a reminder of the wonders still awaiting discovery

Riley Black | The Guardian

Whales used to live on land. This fact never ceases to amaze me. Even though every living species of cetacean – from the immense blue whale to the river dolphins of the Amazon basin – is entirely aquatic, there were times when the word “whale” applied entirely to amphibious, crocodile-like beasts that splashed around at the water’s edge. This week, paleontologists named another.

Peregocetus pacificus – as named by a seven-strong paleontologist team led by Olivier Lambert – is a roughly 42m-year-old mammal that was excavated from the bed of an ancient ocean now preserved in Peru. The prehistoric swimmer wouldn’t have looked like any whale we’re familiar with today. This was a whale that still had arms and legs, the firm attachment of the hips to the spine and flattened toe-tips indicating that Peregocetus was an amphibious creature capable of strutting along the beach. Yet conspicuous expansions to the tailbones of Peregocetus are reminiscent of living mammals, such as otters, that swim with an up-and-down, undulating motion. This was an Eocene preview of the way modern whales move, different from the side-to-side swish of most fish.

Similar fossil whales, such as Maiacetus and Rodhocetus from Pakistan, have been found before. In fact, over the past four decades, paleontologists have uncovered a vast array of early whales that together document how a phylogenetic spray of early amphibious species became at home in the water and set up the evolution of today’s porpoises and humpbacks. But there are two points that make Peregocetus stand out.

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