35^ FOLLOW THE WHALE 



about the middle of this immense stretch of time, the latter in its 

 earlier phases. When we move back again to the Palaeocene, a five- 

 million-year period marking the earliest phase of the Age of Mam- 

 mals (the Tertiary, or Caenozoic Age of geologists), we encounter 

 a complete blank as far as whales are concerned. Our pursuit of the 

 whale backwards in time thus comes to a dead stop about fifty mil- 

 lion years ago in the Eocene Period, as far as the fossil record is con- 

 cerned. This, nevertheless, is by no means the only avenue of pursuit 

 open to us. There is an entirely different channel along which we 

 may follow the whale to very much greater distances in time, if not 

 to its very beginnings. 



Despite their weird, fishy external form and, for mammals, strange 

 habits, almost everything about whales points to their ancestors' hav- 

 ing once lived on land. The only alternative that might be suggested 

 is that they could have been developed directly from some warm- 

 blooded marine reptiles independently of all other mammals. This 

 latter idea is quite untenable for a number of reasons, simple little 

 things which might appear unimportant but which have to be ex- 

 plained. First, whales breathe air, like mammals, birds, reptiles, and 

 amphibians in their adult stage, so their ancestors must have been air- 

 breathers; this precludes fish. The only alternatives are amphibians 

 or reptiles, but these are cold-blooded. Second, they bear their 

 young alive, and then suckle them with milk. Such a process was 

 obviously developed by animals living on land, not in water. Third, 

 many whales have a few hairs left about their jaws and heads, and 

 many more have quite a number before they are born. Hair is an 

 efficient covering for the bodies of land animals, but it is not satis- 

 factory to aquatic creatures. Why, therefore, develop hairs only to 

 get rid of them again? Finally, there are still traces of hind limbs 

 and hip girdles buried in the bodies of some whales, while they have 

 well-developed internal ears and many other anatomical structures 

 which are typical of land animals but which could not be developed 

 directly from the equivalent structures — if any — found in fish, am- 

 phibians, or reptiles. 



If whales are descended from terrestrial mammals, the questions 

 which immediately arise are, from what land animals, and are any 

 of them either still living today or known from fossils? While, as we 

 have seen, the answer to the latter is unfortunately in the negative, 



