Unknown species of ancient four-legged whales discovered in Peru



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Interpretation of the artist Peregocetus pacificus, a four-legged whale of the Middle Eocene.
Illustration: Alberto Gennari

The discovery of a 42-million-year-old fossilized four-legged whale illuminates in a new light the evolution and geographical distribution of these aquatic mammals.

The ancestors of modern whales and dolphins are derived from a small four-legged hoofed animal that lived in Southeast Asia about 50 million years ago, during the Eocene. Fossil evidence suggests that these pioneers of aquatic mammals reached North America 41.2 million years ago, swimming from West Africa to the west. side of the Atlantic. The unexpected discovery of a 42.6 million-year-old unknown quadruped whale along the Peruvian coast has resulted in an important addition to this story: ancient whales have made South America , and not North America, their first home in the New World. The details of this discovery were published today in Current Biology.

The new species is calling Peregocetus pacificus, which suggests "the wandering whale that has reached the Pacific" in Latin. Its remarkably preserved remains were discovered in 2011 on a site called Playa Media Luna, where paleontologists found most of his skeleton, including his jaw, anterior and posterior paws, his spine fragments and his tail. The dating of the marine sediment in which the fossil was found Peregocetus at the middle Eocene.

Interpretation of the artist Peregocetus pacificus walking on the mainland.
Illustration: Alberto Gennari

"This is the first indisputable record of a quadruped whale skeleton for the entire Pacific Ocean, probably the oldest for the Americas and the most complete outside of the world." 39, India and Pakistan ", lead author, Olivier Lambert, paleontologist at the Royal Belgian Institute of Natural Sciences. said in a statement.

Analysis of the Peregocetus The fossils show that it was well suited to both land and sea, with features similar to those of otters and modern beavers. This animal was relatively large, about 4 meters (13 feet) long, more than double that of otters living today. PeregocetusTerrestrial capabilities are evidenced by small hooves at the end of the fingers and by the orientation of the hip bones, suggesting a quadruped gait on the mainland. At the same time, he had tail bones similar to those of beavers and otters, which meant that his tail played an important role in his aquatic abilities. Finally, the size of his fingers and feet suggests webbed appendages, according to the researchers.

The fossilized bones found at Playa Media Luna.
Image: G. Bianucci

The discovery adds new information on the geographic dispersion of ancient whales at this stage of their evolutionary history. According to the researchers, four-legged whales have probably reached South America by crossing the South Atlantic Ocean from the west coast of Africa. The animals would have been assisted by west-facing surface currents and the distance between Africa and South America was about half of what it is today, making walking manageable. Once in South America, Peregocetus settled in Pacific waters along the Peruvian coast, before settling in North America.

"We will continue to search for places as old and even older as those of Playa Media Luna, older amphibian cetaceans. [a group that includes whales and dolphins] can be discovered in the future, "Lambert said.

"This is a truly surprising discovery based on a relatively complete fossil skeleton that shows that very old whales capable of swimming and walking arrived in the Americas much earlier than expected," Erich Fitzgerald, Chief Curator of Vertebrate Paleontology. at Victoria Museums, Melbourne, explained in an email to Gizmodo. "This has really intriguing implications for our understanding of whale evolution. We may not be familiar with this whole chapter of whale evolution in South America and elsewhere on the Pacific and southern coasts, "said Fitzgerald, who is not affiliated with the new study.

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

The paleontologist Felix Marx from the University of Liege in Belgium said that the new study was "significant" but "rather simple" because there is "not much to criticize here", he wrote in an email to Gizmodo. Marx is a good friend of the main author, Lambert, and they share the same desk. It can not therefore "guarantee impartiality". With this warning aside, he says the new fossil is "very convincing" and gives scientists a better idea of ​​how these first whales have spread around the world.

"We have known for a long time that four-legged whales have been able to travel to North America, but this is the first reliable record from South America and therefore also from the first in the world. Southern Hemisphere, "said Marx. "I would be impatient to know how much they really did the south. Who knows, maybe there were former whales on the shores of Chile?

He added, "This study also shows, once again, Peru's great potential as a fossil treasure. It is a world class site, and I hope we will have more surprises if we continue to study it. "

Fitzgerald echoed this sentiment.

"There are clearly more twists in the story of the whale that we have not even begun to imagine," he said. "What is certain is that there are still many cetacean surprises in the southern hemisphere."

[Current Biology]
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