THE BRONTOSAUR AND ITS COUSINS 67 



reptiles in the return of the conditions of the golden 

 age. There was again plenty of water, warmth, and 

 food. Early in the Mesozoic Age they spread over 

 the earth, and grew to enormous proportions, owing 

 to the abundance of food and the relative scarcity of 

 enemies. "Amphibian" to-day means to us a frog 

 or toad or newt, a small and despised thing. In the 

 Mesozoic Age you might have met one peeping out of 

 the water-vegetation with a head three feet long and 

 two feet wide. But the reptiles occupied the same 

 world as they did, and had greater advantages. 

 The amphibians grew less numerous and smaller, 

 approaching more and more to the types that we 

 know to-day. 



The insect world was developing, and we will con- 

 sider this later. In the waters the population was 

 making the same steady and sanguinary progress. 

 The fishes made great advances, the types with bony 

 skeletons now appearing for the first time. Most 

 people are so familiar with fish bones that they can 

 hardly think of a fish without them. Many know, 

 however, that fishes of the skate family have not 

 real bones, but a frame of cartilage. As we should 

 naturally expect, the earlier fishes had skeletons of 

 cartilage, which always precedes bone. 



But the waters were now a worse scene of terror 

 than ever. New types of shark, with the formidable 

 cutting teeth of our shark, though enormously larger, 

 had been evolved. In addition to these there were 



