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 upperjaw-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, 
