Magazine article Science News

Fossil Whale Feet: A Step in Evolution

Magazine article Science News

Fossil Whale Feet: A Step in Evolution

Article excerpt

Paleontologists digging in Pakistan have discovered the 50-million-year-old remains of a whale with legs and feet - a missing link in the evolutionary chain connecting aquatic cetaceans with their landlubbing forebears.

The new-found fossil, called Ambu1ocetus natarts, is the first known ancient whale with large, functional hind limbs, says J.G.M. Thewissen of the Northeastern Ohio Universities College of Medicine in Rootstown. He and his colleagues report their find in the Jan. 14 SCIENCE.

Paleontologist Annalisa Berta of San Diego State University calls Ambulocetus "a very significant discovery. It shows us for the first time a whale that had welldeveloped hind limbs. It's very clear this animal was using its hind limbs in locomotion."

Researchers believe that modern whales descended from four-legged carnivorous mammals, somewhat like large wolves, that once roamed the continents. Sometime around the start of the Eocene period, 57 million years ago, these carnivores gave up their dry lifestyle for one under the waves, forcing their bodies to undergo a profound evolutionary transformation. Among the changes, ancient whales lost their legs and pelvises and developed the characteristic fluked tail that propels these modern leviathans through the seas.

Living whales have no visible hind limbs, but some have internal finger-size bones that are vestiges of hips and legs, an indication that they evolved from land creatures. Three years ago, Philip D. Gingerich of the University of Michigan in Ann Arbor reported the discovery of a 40-million-year-old whale in Egypt that had external legs, although they were too small to help propel the animal (SN: 7/14/90, p.21). Gingerich suggested that this animal, called Basilosaurus, used its tiny hind limbs to grasp its partner during copulation.

While Basilosaurus most likely spent all of its time in water, Thewissen suggests that the sea-lion-size Ambulocetus led an amphibious lifestyle. …

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