GEOLOGICAL EVIDENCES 



383 



Some amphibia are thought to have developed into animals, 

 the reptiles, that breathed with lungs all their lives. The reptiles 

 of the past are called dinosaurs. Those of the earlier Mesozoic 

 period were small, but in the latter part of the period, they be- 

 came more numerous and gigantic in size. The Brontosaurus 

 was nearly seventy feet long. (See page 372.) The Allosaurus 

 was a trifle smaller. It was a dragon-like creature that preyed 

 on its larger but clumsier relatives. 



During this period, the pterodactyl, a huge bat-like animal, 

 appeared. It glided through the air by means of folds of scaly 

 skin extending from the fore-limbs to the side of the body. It 

 had a large bill and a long tail. Its wing-spread was thirty feet. 

 This is probably the animal that was transitional between birds 

 and reptiles. The Archae- 

 opterix was another an- 

 cient birdlike form. It 

 has long, grill-like, true 

 feathers on its wings, a 

 small jaw with teeth, and 

 a vertebrated tail with 

 feathers attached. There 

 were claws on its wings. 

 No transitional animal has 

 been found showing how 

 the scales of the reptiles 

 developed into the feathers 

 of the birds. 



While the birds were 

 developing, a small, very 

 inconspicuous group of 

 animals made their ap- 

 pearance. They had hair 

 instead of scales, and had 



Am. Museum Nat. History 



The Archaeopteryx is the earliest known bird. 

 Two fossil skeletons were found in Bavaria. The 

 creature was about the size of a crow, covered with 

 feathers as in modern birds. Unlike present-day 

 birds, it had uniform teeth in both jaws. It probably 

 used all four limbs in climbing trees. The clawed 

 digits were adapted for this. It is probably an in- 

 termediate form between reptiles and birds. 



