The cetaceans, the group that includes whales and dolphins, they originated in South Asia more than 50 million years ago from a small ancestor of four legs and hooves.
Now, researchers who report on the discovery of an ancient four-legged whale, found in marine sediments of 42.6 million years Along the coast of Peru, they have a new perspective on the evolution of whales and their dispersion to other parts of the world.
According to the researchers, the presence of small helmets on the tip of the whale's fingers and toes and their hip and limb morphology suggest that this whale could walk on land. On the other hand, the anatomical characteristics of the tail and feet, including long and probably webbed appendages, similar to an otter, They indicate that he was also a good swimmer, according to the authors, whose work is published in 'Current Biology'.
"This is the first indisputable record of a quadrupedal whale skeleton for the entire Pacific Ocean, probably the oldest in America and the most complete outside of India and Pakistan," says Olivier Lambert, of the Royal Belgian Institute of Natural Sciences.
A few years ago, the co-author of the study, Mario Urbina, of the Natural History Museum-UNMSM, in Peru, discovered a promising area for dig fossils in the coastal desert of southern Peru, called Media Luna Beach. In 2011, an international team, including members from Peru, France, Italy, the Netherlands and Belgium, organized a field expedition, during which they excavated the remains of an ancient whale that they have since called 'Peregocetus pacificus'. It means "the traveling whale that came to the Pacific."
"By digging around the bones of the outcrop, we quickly realized that this was the skeleton of a quadrupedal whale, with both forelimbs and hind limbs," says Lambert. With the help of microfossils, the sediment layers where the skeleton was placed were accurately dated to the middle Eocene, 42.6 million years ago.
It moved by water and land
The anatomical details of the skeleton allowed them to infer that the animal was capable of maneuvering its large body (up to 4 meters long, with the tail included), both on land and in the water. For example, the characteristics of caudal vertebrae (in the tail) remind those of the beavers and the Otters, which suggests 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 the first cetaceans arrived at The new World across the South Atlantic, from the west coast of Africa to South America, the researchers report.
The whales would have been assisted on their journey by surface currents to the west and by the fact that, at that time, the distance between the two continents was half of what it is today. Scientists suggest that, only after having arrived in South America, amphibian whales migrated north and finally they arrived in North America.
The international team continues to study the remains of other whales and dolphins in Peru. "We will continue to search in locations with layers as old as, and even older than, those of Playa Media Luna, so that the oldest amphibian cetaceans can be discovered in the future," concludes Lambert.