Valley of the Whales

By Tom Mueller

National Geographic Magazine, August 2010

Over thousands of millennia a mantle of sediment built up over its bones. The sea receded, and as the former seabed became a desert, the wind began to plane away the sandstone and shale above the bones. Slowly the world changed. Shifts in the Earth's crust pushed India into Asia, heaving up the Himalaya. In Africa, the first human ancestors stood up on their hind legs to walk. The pharaohs built their pyramids. Rome rose, Rome fell. And all the while the wind continued its patient excavation. Then one day Philip Gingerich showed up to finish the job.

At sunset one evening last November, Gin­gerich, a vertebrate paleontologist at the University of Michigan, lay full length beside the spinal column of the creature, called Basilosaurus, at a place in the Egyptian desert known as Wadi Hitan. The sand around him was strewn with fossil shark teeth, sea urchin spines, and the bones of giant catfish. "I spend so much time surrounded by these underwater creatures that pretty soon I'm living in their world," he said, prodding a log-size vertebra with his brush. "When I look at this desert, I see the ocean." Gingerich was searching for a key bit of the creature's anatomy, and he was in a hurry. The light was failing, and he needed to return to camp before his colleagues started to worry. Wadi Hitan is a beautiful but unforgiving place. Along with the bones of prehistoric sea monsters, Gingerich has found the remains of unlucky humans.

He moved down the spine toward the tail, probing around each vertebra with the handle of his brush. Then he stopped and set down the tool. "Here's the mother lode," he said. Clearing the sand delicately with his fingers, he laid bare a slender baton of bone, barely eight inches long. "It isn't every day that you see a whale's leg," he said, lifting the bone reverently in both hands.

Basilosaurus was indeed a whale, but one with two delicate hind legs, each the size of a three-year-old girl's leg, protruding from its flanks. These winsome little limbs—perfectly formed yet useless, at least for walking—are a crucial clue to understanding how modern whales, supremely adapted swimming machines, descended from land mammals that once walked on all fours. Gingerich has devoted much of his career to explaining this metamorphosis, arguably the most profound in the animal kingdom. In the process he has shown that whales, once celebrated by creationists as the best evidence against evolution, may be evolution's most elegant proof.

"Complete specimens like that Basilosaurus are Rosetta stones," Gingerich told me as we drove back to his field camp. "They tell us vastly more about how the animal lived than fragmentary remains."

Wadi Hitan—literally "valley of whales"—has proved phenomenally rich in such Rosetta stones. Over the past 27 years Gingerich and his colleagues have located the remains of more than a thousand whales here, and countless more are left to be discovered. When we pulled into camp, we met several of Gingerich's team members just back from their own fieldwork. We were soon discussing their results over a dinner of roast goat meat, foul mudamas (fava bean puree), and flatbread. Mohammed Sameh, chief ranger of the Wadi Hitan protected area, had been prospecting for whales farther to the east and reported several new bone piles—fresh clues to one of natural history's great puzzles. Jordanian postdoc Iyad Zalmout and grad student Ryan Bebej had been excavating a whale rostrum poking out of a cliff face. "We think the rest of the body is inside," said Zalmout.

The common ancestor of whales and of all other land animals was a flatheaded, salamander-shaped tetrapod that hauled itself out of the sea onto some muddy bank about 360 million years ago. Its descendants gradually improved the function of their primitive lungs, morphed their lobe fins into legs, and jury-rigged their jaw joints to hear in the air instead of water. Mammals turned out to be among the most successful of these land lovers; by 60 million years ago they dominated the Earth. Whales were among a tiny handful of mammals to make an evolutionary U-turn, retrofitting their terrestrial body plan to sense, eat, move, and mate underwater.

How whales accomplished such an enormous transformation has baffled even the greatest scientific intellects. Recognizing the conundrum as one of the great challenges to his theory of evolution by natural selection, Charles Darwin took a stab at accounting for whales in the first edition of Origin of Species. He noted that black bears had been seen swimming with their mouths open for hours at a time on the surface of a lake, feeding on floating insects. "I can see no difficulty in a race of bears being rendered, by natural selection, more and more aquatic in their structure and habits, with larger and larger mouths," Darwin concluded, "till a creature was produced as monstrous as a whale." His critics poked such loud and gleeful fun at this image, however, that he eventually omitted it from later editions of his book.

Nearly a century later George Gaylord Simpson, the preeminent paleontologist of the 20th century, was still at a loss to explain where whales fit in his otherwise orderly evolutionary tree of mammals. "The cetaceans are on the whole the most peculiar and aberrant of mammals," he remarked peevishly. "There is no proper place for them in a scala naturae. They may be imagined as extending into a different dimension from any of the surrounding orders or cohorts."

If science could not account for the transformation of whales, antievolutionists argued, perhaps it never happened. They contended that land animals that began to adapt to aquatic life would soon be neither fowl nor fish, incapable of surviving in either medium. And if whales really had made this huge transition, where were the fossils to prove it? "The anatomical differences between whales and terrestrial mammals are so great that innumerable in-between stages must have paddled and swam the ancient seas before a whale as we know it appeared," wrote the authors of Of Pandas and People, a popular creationist textbook first published in 1989. "So far these transitional forms have not been found."

Continue to read this article here