50 EXTINCT MONSTERS. 



although not couched in the language used by men of science — to 

 give a fair idea of its structure and habits. 



In conclusion, a few words may be said about the ancestry and 

 life-history of these ancient monsters. Palaeontologists have good 

 reason to believe that they were descended from some early form 

 of land reptile. If so, they show that whales are not the first land 

 animals that have gone back to the sea, from which so many 

 forms of life have taken their rise. 



During the long Mesozoic period fish-lizards played the part 

 that whales now play in the economy of the world; and they 

 resembled the latter, not only in general shape, but in the situation 

 of the nostrils (near the eye), and in their teeth and long jaws. 

 But these curious resemblances must not be interpreted to mean 

 that whales and fish-lizards are related to each other. They only 

 show that similar modes of life tend to produce artificial re- 

 semblances — just as some whales, in their turn, show a superficial 

 resemblance to fishes. 



With regard to the particular form of reptile from which the 

 fish-lizard may have been derived, no certain conclusion has at 

 present been arrived at. This is chiefly from want of fuller 

 knowledge of early forms, such as may have existed in the previous 

 periods known as the Carboniferous and Trias (see Appendix I.). 

 But there are certain features in the skulls, teeth, and vertebrae 

 that suggest a relationship with the Labyrinthodonts, or primaeval 

 salamanders that flourished during the above periods, or~at least 

 from amphibians more or less closely allied to them. They can- 

 not by any possibility be regarded as modified fishes ; for fishes 

 have gills instead of lungs. 



The fish-lizards played their part, and played it admirably ; but 

 their days were numbered, and the place they occupied has since 

 been taken by a higher type — the mammal. As reptiles, they 

 were eminently a success ; but, then, they were only reptiles, and 

 therefore were at last left behind in the struggle for existence, 

 until finally they died out, at the end of the Cretaceous period. 



