430 ELEMENTARY GEOLOGY 
(Ichthyosaurus, etc. (Fig. 252)) swam about in great 
numbers, and immense bat-like forms (Pterodactylus, 
etc. (Fig. 253)) flew through the air. In some places 
we still find the footprints of these various reptilian 
Fig. 248. 
A Mesozoic cephalopod. (Ammonites subradiatus. ) 
types preserved in the rocks; and scales and other 
parts are sometimes preserved, so that there seems to 
have been a wonderful variety of reptile life. 
Birds began to appear in the Mesozoic. ‘These are 
evidently descendants of reptilian ancestors.. Some of 
? 
