National Geographic : 2010 Aug
• molecular biologists studying the cetacean ge- netic code concluded that the whale's closest living relative was one specific ungulate, the hippopotamus. Gingerich and many other paleontologists trusted the hard evidence of the bones more than the molecular comparisons of living ani- mals. ey believed whales had descended from mesonychids. But to test this theory, Gingerich needed to nd one bone in particular. e as- tragalus, or anklebone, is the most distinctive element of the artiodactyl skeleton, because it has an unusual double-pulley shape, with clearly de ned grooves at the top and bottom of the bone like the grooves on a pulley wheel that holds a rope. e shape gives artiodactyls greater spring and exibility than the single- pulley form found in other quadrupeds. (Living whales were of no help, of course, because they have no anklebones at all.) Back in Pakistan in 2000, Gingerich nally saw his rst whale ankle. His graduate student Iyad Zalmout found a grooved piece of bone among the remains of a new 47-million-year- old whale, later named Artiocetus. Minutes later Pakistani geologist Munir ul-Haq found a similar bone at the same site. At rst Gingerich thought the two bones were the single-pulley astragali from the animal's le and right legs--- proof that he'd been right about the origin of whales. But when he held them side by side, he was troubled to see that they were slightly asymmetrical. As he pondered this, manipu- lating the two bones as a puzzler maneuvers two troublesome puzzle pieces, they suddenly snapped together to form a perfect double- pulley astragalus. e lab scientists had been right a er all. Walking back to camp that evening, Gin- gerich and his team passed a group of village children playing dice with the astragali of a goat. (People in various cultures have used the anklebones of domestic artiodactyls in games and fortune-telling for millennia.) Zalmout borrowed one and gave it to Gingerich, then watched in amusement as his professor spent Sand-laden winds sculpt Wadi Hitan's stone outcroppings into exotic shapes that Egyptians call mud lions and sitting sphinxes. Ornate struts of bone on Basilosaurus vertebrae (right) secured huge muscles used to lift and lower the whale's tail and back as it swam.