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.