Cenozoic World

Fossils of the early land-based ancestors of whales have been unearthed in Pakistan.

Scientists say the creatures were a "missing link" between primitive hoofed mammals and the whale family.

The wolf-sized animals ran about on land 50 million years ago.

Other newly found fossils add to the growing picture of how whales evolved from mammals that walked on land.

They suggest that early whales used webbed hind legs to swim, and probably lived both on land and in the water about 47 million years ago.

The four partial skeletons were discovered by palaeontologists from the United States and Pakistan.

Hans Thewissen, of the Northeastern Ohio Universities College of Medicine, Rootstown, USA, was a member of the team that found the two oldest fossils.

One of these ancient creatures was a wolf-sized predator, another the size of a fox.

They belonged to a group called pakicetids.

Long snout

Professor Thewissen said: "The body looks basically like a large dog. The head has all the features of a whale in the teeth and the ear.

"It's different from most land mammals in that the eyes are very close set, the snout is very long and the tail is very muscular and long."

The animals had distinctive ankle bones like those of cloven-hoofed mammals. They also had bones in their ears that are unique to the whale family.

The new fossils superbly document the link between modern whales and their land-based forebears, said Christian de Muizon, of the Centre National de la Recherche Scientifique, Paris, France.

"The first whale was not swimming but walking on land," he said.

Webbed limbs

The two other newly found fossils are of later creatures further down the path towards aquatic life.

The skeletons are approximately 47 million years old, and also come from Pakistan.

These early whales used powerful webbed hind legs to swim, like otters, and could probably move on land as well.

University of Michigan palaeontology professor Philip Gingerich discovered the fossils after a decade-long search.

Professor Gingerich said: It's clear that these animals could hitch their way out of water and back in like sea lions do today, but they were more aquatic than I realised."

Hippo's cousin?

Scientists have long known that whales, dolphins and porpoises - the cetaceans - are descended from land mammals with four limbs.

But this is the first time fossils have been found with features of both whales and land mammals.

The find could help resolve a long-standing debate over the evolutionary link between whales and hippos.

It confirms genetic research placing whales' origin within the ungulate (hoofed animal) group.

And it shows that the whale's closest living relative may well be the hippopotamus.

Wolf-sized: The earliest ancestor of the whale? Image © Carl Buell via link, above

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