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Today's whales and dolphins, skilled swimmers, actually come from a common ancestor over 50 million years ago that possessed legs and it is known that it was originally from South Asia.
Now the remains of one of these ancient whales found in Peru reveal news about the evolution and dispersal of these animals.
The analysis of the bones found in marine sediment has been carried out by an international team of scientists, led by researcher Olivier Lambert from the Royal Belgian Institute of Natural Sciences (Belgium). Their study has been published this week in Current Biology.
The morphology of the fossils suggests that this whale was able to walk on all fours on the land and that, at the same time, it was an excellent swimmer.
According to Lambert, lead author of the study, “This is the first record of a whale skeleton with four legs in the Pacific Ocean, it is probably the oldest ever found in the Americas, and it is the most complete specimen discovered outside of India and Pakistan. ”.
A skeleton full of surprises
A few years ago, study co-author Mario Urbina of the Natural History Museum (UNMSM) in Peru discovered a promising area for fossil digging in the coastal desert in the south of the country, called Media Luna Beach.
In 2011, the team made up of members from Peru, France, Italy, the Netherlands and Belgium organized an expedition during which they unearthed an ancient whale which they have since called as Peregocetus pacificus or "the traveling whale that reached the Pacific”.
"Digging around the outcropping bones, we realized that it was the skeleton of a whale with front and back legs," says Lambert.
With the help of microfossils, the layers of marine sediment were accurately dated to the Middle Eocene, 42.6 million years ago.
Details of the skeleton revealed to scientists that the animal was able to maneuver its large body (up to four meters long, tail included) both by land and by water. The small hooves on the tips of its fingers and its hip, hand and foot morphology indicated that it was able to walk.
Similarly, the anatomical features of the tail and legs, including long, probably webbed appendages, indicated that the animal was also a good swimmer.
"The characteristics of the caudal vertebrae (in the tail) are similar to those of beavers and otters, suggesting that the animal used its tail during swimming," the authors explain.
The ‘first’ to visit the New World
The geological age of this new whale and their presence along the western coast of South America support the hypothesis that these animals arrived across the South Atlantic, from the western coast of Africa to South America.
The surface currents to the west, added to the fact that, at that time, the distance between the two continents was half of what it is today, favored their movement to the American continent.
Researchers suggest that, only after reaching South America, amphibian whales migrated north, finally arriving in North America.
Currently, the team continues to study the remains of other whales and dolphins from Peru. "We will continue to search locations with layers as old, and even older, than those of Media Luna Beach, so that in the future older amphibian cetaceans can be discovered," concludes Lambert.
Lambert et al .: "An amphibious whale from the middle Eocene of Peru reveals early South Pacific dispersal of quadrupedal cetaceans", Current Biology, April 2019, DOI: https://www.cell.com/current-biology/fulltext/ S0960-9822 (19) 30220-9.