Scientists have discovered the fossil of a four-legged whale with webbed feet and hooves in Peru, that thrived both in the sea and on land about 43 million years ago.
The findings, published in the journal Current Biology, provide new insight into whales' evolution and their dispersal to other parts of the world.
The presence of small hooves at the tip of the whale's fingers and toes and its hip and limbs suggest that this whale could walk on land, according to the researchers from the Royal Belgian Institute of Natural Sciences.
They said anatomical features of the tail and feet, including long, likely webbed appendages, similar to an otter, indicate that it was a good swimmer too.
"This is the first indisputable record of a quadrupedal whale skeleton for the whole Pacific Ocean, probably the oldest for the Americas, and the most complete outside India and Pakistan," said Olivier Lambert of the Royal Belgian Institute of Natural Sciences.
Some years ago, researchers discovered a promising area for digging fossils in the coastal desert of southern Peru, named Playa Media Luna.
In 2011, an international team organised a field expedition, during which they excavated the remains of an ancient whale they have since named Peregocetus pacificus.
"When digging around the outcropping bones, we quickly realised that this was the skeleton of a quadrupedal whale, with both forelimbs and hind limbs," Lambert said.
With the help of microfossils, the sediment layers where the skeleton was positioned were precisely dated to the middle Eocene, 42.6 million years ago.
Anatomical details of the skeleton allowed them to infer that the animal was capable of maneuvering its large body (up to four metres long, tail included), both on land and in the water.
Features of the caudal vertebrae (in the tail) are reminiscent of those of beavers and otters, suggesting a significant contribution of the tail during swimming.
The geological age of the new four-limbed whale and its presence along the western coast of South America strongly support the hypothesis that early cetaceans, including whales and dolphins, reached the New World across the South Atlantic, from the western coast of Africa to South America, the researchers said.
The whales would have been assisted in their travel by westward surface currents and by the fact that, at the time, the distance between the two continents was half what it is today.
The researchers suggest that, only after having reached South America, the amphibious whales migrated northward, finally reaching North America.
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