The Story of Evolution 101 



There is no warrant for supposing that the flying reptiles or 

 Pterodactyls gave rise to birds, for the two groups are on differ- 

 ent lines, and the structure of the wings is entirely different. 

 Thus the long-fingered Pterodactyl wing was a parachute wing, 

 while the secret of the bird's wing has its centre in the feathers. 

 It is highly probable that birds evolved from certain Dinosaurs 

 which had become bipeds, and it is possible that they were for a 

 time swift runners that took "flying jumps" along the ground. 

 Thereafter, perhaps, came a period of arboreal apprenticeship 

 during which there was much gliding from tree to tree before true 

 flight was achieved. It is an interesting fact that the problem 

 of flight has been solved four times among animals by insects, 

 by Pterodactyls, by birds, and by bats; and that the four solu- 

 tions are on entirely different lines. 



In the Cretaceous period the outstanding events included 

 the waning of giant reptiles, the modernising of the flowering 

 plants, and the multiplication of small mammals. Some of the 

 Permian reptiles, such as the dog-toothed Cynodonts, were extra- 

 ordinarily mammal-like, and it was probably from among them 

 that definite mammals emerged in the Triassic. Comparatively 

 little is known of the early Triassic mammals save that their back- 

 teeth were marked by numerous tubercles on the crown, but they 

 were gaining strength in the late Triassic when small arboreal 

 insectivores, not very distant from the modern tree-shrews 

 ( Tupaia ) , began to branch out in many directions indicative of 

 the great divisions of modern mammals, such as the clawed mam- 

 mals, hoofed mammals, and the race of monkeys or Primates. 

 In the Upper Cretaceous there was an exuberant "radiation" of 

 mammals, adaptive to the conquest of all sorts of haunts, and 

 this was vigorously continued in Tertiary times. 



There is no difficulty in the fact that the earliest remains of 

 definite mammals in the Triassic precede the first-known bird 

 in the Jurassic. For although we usually rank mammals as 

 higher -than birds (being mammals ourselves, how could we do 



