20 



ANIMALS OF THE PAST 



and that not only shows the teeth and spines but the 

 faint imprint of the body and fins as well. And from 

 such rare examples we learn just what teeth and spines 

 go with one another, and sometimes find that one fish 

 has received names enough for an entire school. 



These ancient sharks were not the large and powerful 

 fishes that we have to-day these came upon the scene 



THE SKULL AND JAWS OF DINICHTHYS 

 In the American Museum of Natural History. 



later but mostly fishes of small size, and, as indicated 

 by their spines, fitted quite as much for defence as 

 offence. Their rise was rapid, and in their turn they 

 became the masters of the world, spreading in great 

 numbers through the waters that covered the face of the 

 earth; but their supremacy was of short duration, for 



