Peregocetus: Bizarre, Prehistoric Four-legged Whale With Hooves and Otter-like Tail Discovered

An ancient whale that had four legs, hooves and an otter-like tail has been discovered in marine sediments on the coast of Peru. The 13 foot creature lived around 42.6 million years ago and appears to have been able to walk on land and swim in the sea.

The find raises questions about the evolution of cetaceans—the group that includes whales and dolphins. According to the U.K.'s Natural History Museum, the land-based ancestors of cetaceans lived around 50 million years ago. But at some point the goat-sized creature Pakicetus—found in what is now Pakistan and India—ended up back in the sea. From this the group evolved, eventually resulting in the species we see today.

The first four-legged whales were largely confined to Asia. The latest discovery shows they had managed to cross the Atlantic and set up home in the Americas. The creature has been named Peregocetus pacificus, which means "the traveling whale that reached the Pacific." Details of its discovery have now been reported in the journal Current Biology.

In the paper, the team, led by Olivier Lambert, of the Royal Belgian Institute of Natural Sciences, say Peregocetus measured 13 foot in length and had small hooves on the tips of what would have been its feet. It had a large tail similar to what is seen today in otters and beavers, as well as webbed appendages. Analysis of its morphology indicates it could have walked on land—but was probably a very good swimmer.

Peregocetus pacificus
Artist impression of Peregocetus pacificus. A. Gennari

"It most likely spent most of its time in the water, especially for feeding, as it was certainly better at swimming than walking, but it may have moved back to land to rest, maybe to breed and for other social interactions, and possibly also to give birth," Lambert told Newsweek.

He said Peregocetus's features were a "very unusual combination for an amphibious mammal." It had a relatively long snout "with robust teeth." This, he said, indicates that Peregocetus fed in the sea on medium-sized fish by catching prey with its incisors then cutting it up into pieces with its shearing molars.

Other ancient whales, he added, were generally more similar to those found in Pakistan—but did not tend to have an otter-like tail. "Outside India and Pakistan, skeletons of early quadrupedal whales are generally not as complete, making the comparison more difficult. But for example in Georgiacetus, from the U.S., the hip was not as tightly attached to the sacrum, meaning that this animal faced more difficulties to move on land."

The team believes Peregocetus got to Peru by swimming across the South Atlantic—the distance of this would have been half what it is today because of the movements of the continents. From here, amphibious whales could have moved north and eventually reached North America.

left mandible of Peregocetus
left mandible of Peregocetus. O Lambert

Lambert said they now plan to continue searching for more specimens in Peru's Pisco Basin: "Maybe we will find the skull of Peregocetus, and geologically older amphibious whales," he said.

Jonathan Geisler, an expert on the evolutionary history of mammals at the New York Institute of Technology, who was not involved in the research, told Newsweek the discovery of an archaic whale in Peru was surprising.

"The leg and foot anatomy is similar to that seen in older whales from Pakistan, so this discovery raises important questions about the routes early whales took to disperse around the globe as well as how effective they were moving through the water," Geisler said. "Were they restricted to coastal waters, or could they cross ocean basins? I am excited to see if this team can find more early whales in Peru."

Travis Park, from the Natural History Museum in the U.K., said the paper helps fill gaps in our understanding of how whales came to dominate the oceans. "It's also another example of the fantastic fossils that continue to be found in Peru, where there seems to be no end to the new discoveries," he told Newsweek.