Unknown species of ancient four-legged whale discovered in Peru

Artistic interpretation of Peregocetus pacificus, a four-legged whale from the Middle Eocene.
The artist's interpretation of Peregocetus pacificus, a four-legged whale of the Middle Eocene.
Illustration: Alberto Gennari

The discovery of a fossilized four-legged whale, 42 million years old, is shedding new light on the evolution and geographic distribution of these aquatic mammals.

The ancestors of modern whales and dolphins evolved from a small four-legged animal and hooves that lived in South Asia about 50 million years ago, during the Eocene. Fossil evidence suggests that these pioneers of aquatic mammals arrived in North America 41.2 million years ago, swimming from West Africa across the Atlantic. The surprising discovery of a 42.6 million year old quadrupedal whale that was unknown along the coast of Peru has resulted in an important appendix to this story: ancient whales made South America, not America. North, his first home in the New World. . The details of this discovery were published today in Current Biology.

The new species is called Peregocetus pacificus, which suggests "the traveling whale that came to the Pacific" in Latin. Their well-preserved remains were found in 2011 at a place called Playa Media Luna, where paleontologists recovered most of their skeleton, including its jaw, front and back legs, fragments of spine and tail. Dating of the marine sediments within which the fossil was found. Peregoceto to the middle Eocene.

Artistic interpretation of Peregocetus pacificus walking on land.
The artist's interpretation of Peregocetus pacificus walking on land.
Illustration: Alberto Gennari

"This is the first undisputed 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," lead author Olivier Lambert, a paleontologist at the Royal Belgian Institute of Sciences Natural he said in a statement.

Analysis of the Peregoceto The fossils show that it was well adapted to both land and sea, with characteristics similar to modern otters and beavers. This animal was relatively large, measuring about 4 meters (13 feet) in length, which is more than twice the size of the otters that live today. PeregocetoTerrestrial abilities were evidenced by small helmets at the tips of his fingers and the orientation of his hip bones, suggesting a quadruped gait on the ground. At the same time, he had tail bones similar to those of beavers and otters, which means that his tail played an important role in his aquatic abilities. Finally, the size of their fingers and feet suggests webbed appendages, according to the researchers.

The fossilized bones were recovered in Media Luna Beach.
The fossilized bones were recovered in Media Luna Beach.
Image: G. Bianucci

The discovery adds new knowledge about the geographical spread of ancient whales at this stage in their evolutionary history. The four-legged whales probably arrived in South America crossing the South Atlantic Ocean from the west coast of Africa, according to the researchers. The animals would have been badisted by surface currents to the west, and the distance between Africa and South America was about half of what it is today, which makes the trip manageable. Once in South America, Peregoceto They settled in the Pacific waters along the Peruvian coast, and eventually moved to North America.

"We will continue to search in locations with layers as old, and even older, than those of Media Luna Beach, making the oldest amphibian cetaceans [a group that includes whales and dolphins] It may be discovered in the future, "said Lambert.

"This is a genuinely surprising discovery based on a relatively complete fossil skeleton that shows that truly ancient whales capable of swimming and walking arrived in the Americas much earlier than previously thought," Erich Fitzgerald, chief curator of vertebrate paleontology at Museums Victoria , Melbourne, explained in an email to Gizmodo. "It has really interesting implications for our understanding of the evolution of whales. There may be this whole chapter in the history of the evolution of whales that happened in South America and other parts of the Pacific and southern coasts that we did not know about, "said Fitzgerald, who is not affiliated with the new study.

Reconstruction showing the preserved parts of the skeleton of Peregocetus pacificus, both in terrestrial and aquatic configurations.
Reconstruction that shows the preserved parts of the Peregocetus pacificus Skeleton, both in terrestrial and aquatic configurations.
Image: Olivier Lambert et al., 2019 / Current Biology

Paleontologist Felix Marx, of the University of Liege in Belgium, said the new study is "significant" but "fairly simple", since "there is not much to criticize here," he wrote in an email to Gizmodo. Marx is a good friend of Lambert, the main author, and they share the same office, so he could not "guarantee impartiality". Leaving aside the disclaimer, he said the new fossil is "very convincing," and is giving scientists a better idea. How these first whales spread around the world.

"We have known for a time that four-legged whales had arrived in North America, but this is the first reliable record in South America and, therefore, also the first in the southern hemisphere," said Marx. "I'll be anxious to know how far south they really did it – who knows, maybe there were once ancient whales off the coasts of Chile too?

To which he added: "This study also shows, once again, the great potential of Peru as a fossil treasure. It's a world-clbad site, and I hope we have more surprises as we continue to study it. "

Fitzgerald echoed this sentiment.

"There are clearly more twists in the history of the whale that we have not even begun to imagine," he said. "What is certain is that there are many more surprises of cetaceans waiting to be discovered in the southern hemisphere."

[Current Biology]

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