Paleontologists have found a well-preserved fossil that is the missing link in cetaceans that returned to the sea. The 43-million-year-old whale with four legs, webbed feet and hooves has been discovered in Peru.
The giant 42.6m-year-old fossil, discovered in marine sediments along the coast of Peru, appears to have been adapted for a semi-aquatic lifestyle.
With four limbs capable of carrying its weight and a powerful tail, the semi-aquatic whale has been compared to an otter or a beaver.
Researchers believe the discovery could shed light on the evolution of the whale and how it spread.
The new species is called Peregocetus pacificus, which translates to “the traveling whale that reached the Pacific” in Latin. Its remarkably well-preserved remains were found in marine sediments 1km (0.6 miles) inland Peru, at a site called Playa Media Luna. Where paleontologists recovered most of its skeleton, including its jaw, front and hind legs, bits of spine, and tail. Dating of the marine sediment within which the fossil was found places Peregocetus to the middle Eocene.
The ancestors of whales and dolphins walked on Earth about 50 million years ago in the regions that now comprise India and Pakistan.
We usually think of mammals as having evolved out of the sea and onto land, but for whales, that process ran backwards. The earliest known whale fossils from India and Pakistan show a species that transitioned back into the oceans in south Asia.
Paleontologists have previously found partial fossils of the species in North America that were 41.2 million years old suggesting that by this time, the cetaceans had lost the ability to carry their own weight and walk the Earth.
"This is the most complete specimen ever found for a four-legged whale outside of India and Pakistan," Dr Olivier Lambert, a scientist at the Royal Belgian Institute of Natural Sciences and co-author of the study, said.
It was found in marine sediments 1km (0.6 miles) inland from Peru's Pacific coast, at Playa Media Luna.
The location has piqued researchers' interest as the first whales are thought to have first evolved in South Asia around 50 million years ago.
As their bodies became better suited to water, they migrated further afield to North Africa and North America, where fossils have been found.
The latest discovery suggests early whales managed to swim there from South America.
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 Peruvian fossil suggests the first whales would have crossed the South Atlantic, helped by westward surface currents and the fact that, at the time, the distance between the two continents was half what it is today.
The last few tail vertebrae are missing and so it is not clear if the creature’s tail would have featured the large paddle, known as a fluke, that allows some modern whales to power themselves along at speeds of more than 30mph (48 km/h). But it must have been an accomplished swimmer to have survived for days or even weeks at sea.
Based on its anatomy, the scientists say this cetacean of about 13 feet (four meters) long could both walk and swim. Its sharp teeth and long snout suggest the early whales may have eaten fish or crustaceans.
According to a new study in Current Biology, microfossils located near the main find date the creature as 42.6 million years old.
"Whales are this iconic example of evolution," Travis Park, an ancient whale researcher at the Natural History Museum in London, said.
"They went from small hoofed mammals to the blue whale we have today. It's so interesting to see how they conquered the oceans."
Older and smaller whale ancestors with four limbs had been discovered previously, but the latest specimen fills in a crucial gap in knowledge about how the creatures evolved and spread throughout the world’s oceans.
An international team of palaeontologists from Peru, France, Italy, the Netherlands, and Belgium excavated the fossil in 2011.
They have named it Peregocetus pacificus, meaning "the travelling whale that reached the Pacific".