Fossil Reveals Ancient Whale Was Able to Move on Land

Researchers have found the fossil remains of an ancient relative of the whale that was able to propel itself on land.

“This critter is a missing link between land animals and modern whales,” said J.G.M. Thewissen, a paleobiologist at Northeastern Ohio Universities College of Medicine in Rootstown, Ohio. “It is a very complete specimen and has enough of the anatomy to teach us something about how the animal moved on land.”

A report on the discovery is to be published today in the journal Science.

Thewissen said the fossil was found in deposits left by an ancient sea that once existed in Pakistan. Fossils found nearby suggest that the whale died about 50 million years ago.

“It was about the size of a big male sea lion and probably weighed 600 to 700 pounds,” Thewissen said.

Many fossils of the land-dwelling ancestors of the modern whale have been found, but Thewissen said this is the first with enough fossils of the legs, vertebrae and tail to show how the animal was able to move on land and in the water.

The animal, which Thewissen calls Ambulocetus natans, had large rear feet with fully developed legs. In front, the feet are short, stubby and joined almost to the shoulder.

As a result, the whale moved by bumping along on its chest and abdomen, lifting itself just enough to lurch forward.

Ambulocetus natans had the teeth of a carnivore, but because it was so awkward on land it probably was unable to catch prey out of the water. For this reason, Thewissen speculates that the whale ancestor lived on marine life, as do modern whales.

Modern whales are thought to have developed from animals that lived on land and slowly, over thousands of generations, evolved to the oceangoing mammal known today.

“The oldest skeleton that is a marine whale is about 40 million years old,” Thewissen said. That skeleton is 40 to 50 feet long and had tiny hind feet inadequate for moving on land.

Ambulocetus natans lived about 10 million years before that, but Thewissen said there are a number of missing links in the evolutionary chain to the modern whale.