About 43 million years ago, when South America was surrounded by water on all sides, there lived a whale with four legs, elongated toes, sharp teeth and perhaps even fur.
This ancient creature looked more like the love child of an otter and a crocodile than any modern-day whale. And, unlike today’s whales, which dwell exclusively in the sea, this animal lived some of its life on land.
“I think they were not very good at walking, and certainly not at running,” said Olivier Lambert, a vertebrate paleontologist at the Royal Belgian Institute of Natural Sciences.
The whale fed at sea and probably only came on land for specific activities that could have included breeding or giving birth, Lambert said. That would be similar to the behavior of seals and sea lions today.
The fossilized bones, discovered in Peru’s Pisco Basin in 2011, were embedded among marine deposits that dated back about 42.6 million years, to the middle Eocene Epoch.
“We found a really incredible specimen,” said paleontologist Rodolfo Salas-Gismondi of Cayetano Heredia University in Lima, who was part of the team that reported the find in the journal Current Biology.
The study authors dubbed it Peregocetus pacificus, or “the traveling whale that reached the Pacific.” The name honors its role in helping scientists understand how early whales migrated from the Mediterranean to the Atlantic and eventually to the New World, said Lambert, the lead author.
Whales are descended from artiodactyls, a group of mammals that includes cows, sheep, goats and other hoofed animals. The earliest four-legged whales from Pakistan and India lived in shallow rivers, said Hans Thewissen, an anatomist and paleobiologist. “Those early animals are amphibious, but they are not very good swimmers. At some point they learn to be better swimmers and learn how to cross big oceans,” he said.
Hind legs likely helped Peregocetus’ ancestors swim from the northern coast of Africa to South America, Lambert said. As whales spent more time swimming, they gradually lost their hind limbs, which interfered with a swimming motion that relied primarily on tail movement, Lambert said. “The tail is much more efficient for locomotion than a combination of tail and hind limbs,” he said.