62 WATER REPTILES OF THE PAST AXD PRESENT 



examples of the adaptation of air-breathing animals to an aquatic 

 life than the great whalebone whales. In Eocene times their 

 ancestors were walking and running land animals; of that there 

 can be not the slightest doubt, since we cannot conceive, as did the 

 older naturalists, of their direct descent from the fishes while having 

 all the essential structure of mammals, i.e., lungs, circulatory sys- 

 tem, manner of breeding and rearing the young, etc. Of the living 

 whales, or Cetacea, there are now in existence two very distinct 

 types, so different from each other that some have supposed them 

 to have been evolved from different types of land mammals. One of 

 these is best exemplified by the great baleen whale, having a broad, 

 short head and no teeth. It feeds upon crustaceans chiefly, which 

 are strained from the water by the great fringe or net of "whale- 

 bone." The other type is seen in the porpoise or dolphin. These 

 cetaceans have numerous, pointed and recurved teeth, which they 

 use as did many of the reptiles, hereinafter described, for the seizure 

 and retention of fishes and other swimming animals. So great have 

 been the changes in all these cetaceans, in the adaptation to an 

 aquatic fife, that we are almost at a loss to conjecture from what 

 kinds of land animals they have descended. The great zeuglodont 

 whales of early Tertiary times have long been thought to be a sort 

 of connecting link between them and their land ancestors, and it 

 is still probable that they were. The forms of zeuglodont whales 

 that have been discovered in Africa within recent years bear so 

 much resemblance in their skull and teeth to the contemporary 

 carnivores, that many paleontologists think, with good reason, that 

 they were descended from them, that is, from the ancestors of all 

 our dogs, cats, weasels, bears, etc., of modern times. And we have 

 much reason to believe that future discoveries will bring further 

 and more decisive proof of their origin ])efore many years have 

 elapsed. The modern Sirenia, the dugongs and manatees, exclu- 

 sively aquatic mammals, which feed upon seaweeds at the bottoms 

 of shallow bays and harbors, or in the mouths of rivers, are now 

 known, practically with certainty, to be the descendants in these 

 same African regions of the earliest ancestors of our sheep, oxen, 

 and horses, known so certainly that they are often classed with 

 them, or at least with the elephants, which approach them in their 

 ancestral line even more closely. 



