An ancient four-legged whale with hooves has been discovered, providing new insights into how the ancestors of the Earth's largest mammals made the transition from land to sea.
The last few tail vertebrae are missing and so it is not clear if the creature's tail would have featured the large paddle, known as a fluke, that allows some modern whales to power themselves along at speeds of more than 30mph (48 km/h).
Pieces of four-legged whales were found in Egypt, Nigeria, Togo, Senegal and Western Sahara, but they were so fragmented that it was impossible to decisively conclude whether they could swim.
The ancestors of modern whales and dolphins evolved from a small, four-limbed hoofed animal that lived in south Asia around 50 million years ago, during the Eocene. It has since been named Peregocetus pacificus, meaning "the travelling whale that reached the Pacific". After reaching South America, it is believed the whales then migrated northward towards North America, where other fossils have been found.
"T$3 he anatomy of the first vertebrae of the tail resembles that of amphibious mammals such as otters and beavers", says Lambert. A lot about the odd evolution of whales is already well known, but what is less understood is how they got from Pakistan and India to the rest of the world. The fossil was so well preserved the researchers were able to find the animal's kneecap and small anklebones, and they could see that the finger and toe bones bore traces of tiny hooves. That's probably how they crossed the Atlantic Ocean, researchers said.
The specimen proves that early whales could swim for days or possibly weeks at a time while retaining the ability to walk on land.
For example, its hind feet bones had ridges to which ligaments and tendons would attach, suggesting it had webbed feet.
According to the surprisingly well-preserved fossil, the animal would have been around 11 feet long. The latest discovery shows they had managed to cross the Atlantic and set up home in the Americas.
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"A skull would be great, as well as the tip of the tail", Lambert said.
These aquatically capable creatures initially spread out from Southern Asia, taking millions of years to spread around the world into the hippos and whales commonly known today. 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 fossil was excavated in 2011 by an global team of palaeontologists from Peru, France, Italy, the Netherlands, and Belgium.
The Peruvian whale ancestor fossil is the oldest of its kind discovered in the New World at 42.6 million years old.
The findings were reported in the journal Current Biology.
But who's to say where they'll be roaming in another 50 million years?
Mammals began to appear around 200 million years ago, but came into their own only when the dinosaurs were wiped out 65 million years ago.
There are many intermediary stages of this "spectacular evolutionary history" that have been found over the years, "but we still miss elements, so we should keep searching in other parts of the world, especially in the Southern Hemisphere, for skeletons of these unusual four-legged whales, to make the whole scenario better understood", Lambert said.
Seals and sea lions are closely related to dogs, while manatees share ancestry with elephants.