PEOPLING OF LAND AND SEA 187 



first become a hopping creature, whose feathers, developed 

 quite independently, perhaps even before it acquired that 

 aptitude for hopping, later permitted flight. The only Reptiles 

 which have been preserved to us — we shall see why later 

 (p. 276) — are those whose method of progression was of the 

 humblest order. During the course of the Secondary Period, 

 however, certain Reptiles acquired dimensions of which even 

 Whales scarcely give us an idea, and nearly all had 

 developed modes of locomotion analogous to those of existing 

 Mammals. While many of them had bodies still sunken low 

 on the legs and trailed on the ground, like Crocodiles and 

 Lizards, others had straightened their limbs in such a way as 

 to permit the body to be carried high, dog-fashion, and a 

 number of others stood almost erect on their hind legs, like the 

 Kangaroo. It is among these last that we ought to look for 

 the ancestor of the Birds. This ancestor would have already to 

 possess the characters common to all : he must stand erect 

 with the sole of his foot straightened on his toes, five in number 

 at first, and his three median metatarsals, supporting the 

 upright sole of his foot, must unite in a single rod. The fibula 

 would be rudimentary, and united with the tibia at either 

 extremity. Now there exists to-day a Mammal whose hind 

 feet display most of these characteristics. This is the Jerboa, 

 or leaping Mammal par excellence. The union of the metatarsals 

 is seen also in Ruminants, the fleetest of the Mammals, whose 

 method of progression is nothing but a series of bounds. The 

 Bird, then, must be descended from a leaping and probably 

 arboreal Reptile. The a posteriori verification of this con- 

 clusion is provided by those Birds which have lost the faculty 

 of leaping, like Auks and Penguins, and which are essentially 

 swimmers and walkers, or the Parrots, which, instead of 

 hopping from branch to branch like Sparrows, hoist themselves 

 up using their hook-shaped beaks in the process. In both these 

 quite different cases, with nothing in common but the abandon- 

 ment of the leaping habit, the metatarsus is shortened and 

 broadened, and the three bones which united to form it are 

 tending to become isolated again. 



From this vantage point we might be tempted to look for 

 the primitive Bird among those present-day birds unable to 

 fly : the African Ostriches, the South American Nandus, the 

 Indian Cassowaries, the Australian Emus, the New Zealand 



