some 130 million years from the appearance of animals 

 smaller than a foot in size to the final extinction of the great 

 dinosaurs over one hundred times as large, was eliminated 

 by the changing environment in which major mountain- 

 building activity took place. The previously swampy river 

 deltas in which the giant dinosaurs lived were thus sub- 

 merged as the coastal land sank along the edges of the 

 newly rising mountain ranges, which included the Rocky 

 Mountains, the Andes, and many European ranges. The 

 dinosaurs had in fact become so specialized to suit their 

 environment that they were unable to survive in different 

 conditions. 



The evolutionary line of the elephants, which still con- 

 tinues today although the number of these animals is 

 diminishing rapidly as man alters their natural environ- 

 ment, began in the Eocene period (about 70 million years 

 ago) as the primitive mammals of the Cretaceous gave 

 rise to many modern types. By the time of the following 

 Oligocene period there had evolved small elephants with 

 short trunks and tusks in both jaws, and during the Mio- 

 cene these produced ever larger elephants which spread 

 from Africa to Europe, Asia, and America. In the Pliocene 

 period elephants continued to thrive, and in the succeed- 

 ing Pleistocene considerably larger elephants appeared. 

 However the Ice Age occurring in this last period caused 

 several elephant types, e.g. the woolly mammoths, to die 

 out. These huge creatures were cut off from escape to the 

 south by the advance of the glaciers and snow in Siberia, 

 and in fact completely preserved specimens have been 

 found buried in the ice. It thus appears that the elephant 

 line would have a duration exceeding some 70 million 

 years if its environment had not been radically altered, 

 since these animals are weU adapted to their normal jungle 



8 



