42 EXTINCT MONSTERS. 



have been preserved, since those of fishes and crocodiles of 

 the Jurassic period have been found in considerable number 

 and variety. It is therefore safe to conclude that such were 

 absent in this case. In the Lias strata, at least, the specimens 

 are often preserved with most wonderful completeness (see 

 P- 47). 



The long and pointed jaws are a striking feature of these 

 animals. The eyes were very large and powerful, and specially 

 adapted, as we shall see presently, to the conditions of their life. 



It might, perhaps, be asked whether the fish-lizards breathed, 

 like fishes, by means of gills. That question can easily be 

 answered ; for if they had possessed gills for taking in water and 

 breathing the air dissolved therein, they would reveal the fact by 

 showing a bony framework for the support of gills, such as are to 

 be found in all fishes. These structures, known as " branchial 

 arches," are absent ; therefore the fish-lizards possessed lungs, and 

 breathed air like reptiles of the present day. Their skulls show 

 where the nostrils were situated ; namely, near the eyes, and not 

 at the end of the upper jaw-bone. There are also passages in the 

 skull leading from the nostrils to the palate, along which currents 

 of air passed on their way to the lungs. Being air-breathers, they 

 would be compelled occasionally to seek the surface of the sea, in 

 order to obtain a fresh supply of the life-giving element oxygen ; 

 but, being cold-blooded and with a small brain, needing a much 

 less supply of oxygen for its work, the fish-lizards had, like fishes, 

 this advantage over whales, which are warm-blooded that their 

 stern-propeller, or tail-fin, could take the form best adapted for a 

 swift, straight-forward course through the water. 



In the whale tribe the tail-fin is horizontal ; and this is so on 

 account of their need, as large-brained, warm-blooded air- 

 breathers, of speedy access to the atmospheric air. Were it other- 

 wise, they would not have the means of rising with sufficient 

 rapidity to the surface of the sea ; for they have only one pair of 

 fins. But the fish-lizards had two pairs of these appendages, 



