198 THE STORY OF REPTILE LIFE. 



trunk, as in the whales and porpoises of to-day, 

 these "Fish-lizards" nevertheless bear a sufficiently 

 close structural resemblance to the long-necked 

 " Sea-lizards " or Plesiosaurs to justify the older 

 naturalists in regarding them as closely allied 

 forms. A more complete knowledge of their 

 anatomy, however, has since shown that in reality 

 they are probably not in any way related. What 

 their origin may have been, however, we do not 

 know. That they were derived from terrestrial 

 creatures there can be no doubt, though no such 

 terrestrial types such as lead up to the Plesio- 

 saurs are known. Instead, these strange crea- 

 tures appear suddenly in time with all their 

 specialised features in full development. In 

 shape, we may repeat they were strangely whale- 

 like, at least these are the forms which they are 

 considered to-day to most nearly resemble. The 

 older naturalists, however, seem to have con- 

 sidered them more fish-like, hence the name by 

 which they are scientifically known Ichthyosaurs, 

 " Fish-lizards." The earliest known species occur 

 at the very base of the secondary system of 

 zoological deposits, occurring in what is known 

 as the New Eed Sandstone of the Triassic era. 

 But it is in the Lias that their remains are best 

 preserved, though they lived on till the end of 

 the Cretaceous system. . It is a point of extreme 

 interest to note that, as with many other types 

 described in earlier chapters of this book, we 

 have evidence of specialisation having taken 

 place among these singular creatures in response 

 to a change in the character of the food. For 

 whilst the earlier species invariably have the 



