WASHINGTON – Scientists have unearthed fossils in a coastal desert in southern Peru of a four-legged whale that thrived both in the sea and on land about 43 million years ago in a discovery that illuminates a fundamental stage in the early evolution of the cetaceans.
The 13-foot-long mammal, called Peregocetus pacificus, represents a crucial intermediate step before the whales adapt fully to a marine existence, the scientists said Thursday.
Their four limbs were able to support their weight on land, which means that Peregocetus could return to the rocky shore to rest and perhaps give birth while spending much of their time at sea. Their feet and hands had small helmets and were probably webbed to help swim. With long fingers and toes, and relatively thin limbs, moving on land may not have been easy.
Its elongated snout and sturdy teeth, large incisors and canine teeth together with molars that cut through the flesh, made Peregocetus an adept at capturing medium prey like fish.
"We think he was feeding on the water and that his underwater locomotion was easier than on land," said the 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 share strong similarities with semi-aquatic mammals such as otters, indicating that the tail was used predominantly for underwater locomotion," Lambert added.
The evolutionary origins of the whales were little known until the 1990s, when fossils of the first whales were found. Several fossils have shown that whales evolved a little more than 50 million years ago in Pakistan and India from mammals living in the field and living on land, which are distantly related to hippos and size. of a medium-sized dog. It took millions of years for them to spread throughout the world.
Peregocetus represents the most complete quadrupedal whale skeleton outside of India and Pakistan, and the first known of the Pacific region and the southern hemisphere.
Their presence in Peru, said Lambert, suggests that quadrupedal whales extended from southern Asia to northern Africa, then crossed the South Atlantic to reach the New World. Peregocetus shows that the first whales that arrived in America still had the ability to move on land.
Over time, the forelimbs of the cetaceans evolved to become fins. The hind legs finally become mere vestiges. It was not until about 40 million years ago that the lineage of the whales evolved into fully marine animals, and then split into two groups of cetaceans alive today: paca whales that feed by filtration and toothed whales like dolphins and killer whales.