transition of whales from land to sea. I also 

 reasoned that we need not remain in the 

 dark. After all, whales live and die in 

 water, where they are easily buried and 

 fossilized, and their fossils are large and 

 relatively easy to find. Furthermore, ma- 

 rine rocks of Eocene age cover vast areas 

 of the earth's surface. Since finding Pa- 

 kicetus, my colleagues and I have been ex- 

 ploring whenever possible the deserts of 

 Pakistan and Egypt for whales to fill the 

 gaps in our knowledge. Our results have 

 been gratifying. 



In 1989, 1 was working with paleontolo- 

 gists Elwyn Simons and Holly Smith in 

 Tethyan sediments of the Egyptian Sahara, 

 where we found another archaeocete. In 

 addition to a hefty, four-foot-long skull 

 and huge ribs, we found a thigh bone, then 

 lower leg bones, then an ankle. Finally, we 

 also unearthed, one by one, three tiny toes. 



These, the first complete hind limbs and 

 feet of an archaeocete to be discovered, 

 belonged to the forty-million-year-old 

 Basilosaums isis, a large early whale that 

 must have been one of the most ferocious 

 marine carnivores of its time. Because the 

 hind limbs (about eighteen inches long) 

 were not connected to a sacrum in the 

 spinal column as are the hind limbs of land 

 mammals, Basilosaums could not possi- 

 bly have used its feet to lift or support its 

 eellike, fifty-foot-long body. Yet the bones 

 and joints are so well formed, with strong 

 processes for the attachment of muscles, 

 that the Umbs appear to have been func- 

 tional. I suspect that Basilosaums used its 

 legs and feet as guides during copulation. 

 Basilosaums exhibits not only an un- 

 usually elongated shape but also oddly 

 proportioned vertebrae that lead me to be- 

 lieve that it was on a side line, rather than 



on the main path to the evolution of mod- 

 em whales. Another cetacean from the 

 same era, found in Egypt and known as 

 Prozeuglodon atrox, combines normally 

 proportioned vertebrae with hind limbs 

 much like those of Basilosaums and is a 

 better candidate for a direct ancestor of 

 modem whales. 



Paleontologists have long believed that 

 because whales evolved from land mam- 

 mals, they must have had hind limbs and 

 feet early in their history. What surprised 

 me most about finding hind limbs on 

 Basilosaums and Prozeuglodon was that 

 these archaeocetes lived ten million years 

 after Pakicetus and the origin of whales. 

 Ten million years is a long time, even to a 

 geologist, and finding hind limbs on such 

 "late" whales means that the transition 

 from land to sea took time — time enough 

 to allow us to study the intermediate stages 



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