A four-legged whale: the missing link on the Peruvian coast

Scientists have discovered on the south coast of Peru the fossils of a four-legged whale that lived both on land and in the sea 43 million years ago, a discovery that illuminates a crucial step early stages of cetacean evolution. .

The mammal Peregocetus Pacificus, four meters long, represents an intermediate link before the complete adaptation of whales to the sea, scientists said Thursday.

His four legs allowed him to move on land, which means that the Peregocetus could return to the rocky coast to rest and perhaps give birth, although he had spent a good part of his life in the sea.

The front and back legs wore small helmets probably held by a sail to help him swim. Their long fingers and relatively thin limbs suggest that moving over the land would not have been easy.

Its elongated snout and sturdy teeth, its large incisors and canines to grasp, as well as its molars capable of cutting meat, have made Peregocetus an adept of medium prey, such as fish.

"We think that he was fed in water and that his underwater locomotion was easier than on land," said paleontologist at the Royal Belgian Institute of Natural Sciences, Olivier Lambert , who led the research published in the journal Current Biology.

"Some vertebrae in the tail region have great similarities to those of aquatic mammals such as otters, which indicates that they used the tail mainly for transfer under water," added Mr. Lambert.

The evolutionary origins of whales were little known until the 1990s, when fossils of the first cetaceans were discovered.

Several of these fossils have shown that whales evolved about 50 million years ago in Pakistan and India from land-based mammals, which are to some extent related to hippopotamuses and are about the size of the sea. 39, a medium sized dog. It took millions of years to spread around the world.

The Peregocetus represents the most complete quadruped whale skeleton that can be found outside of India and Pakistan and the first known in the Pacific and Southern Hemisphere.

According to Lambert, their presence in Peru suggests that four-legged whales extend from southern Asia to northern Africa, and then crossed the South Atlantic for reach the New World. The Peregocetus proves that the first whales arrived in America still had the ability to move on land.

Over time, the forelimbs of the cetaceans turned into fins and the hind limbs eventually became mere remains.

It is only about 40 million years ago that the whale line has been transformed into fully marine animals, and then divided into two groups of live cetaceans: filter-feeding whales and tooth-like whales. dolphins and killer whales. .