14 THE EVOLUTION OF MAN. 



Reptiles, Birds, and Mammals must have belonged, seems 

 in fact to be referred by these oldest reptilian remains back 

 to the close of the Palaeolithic Epoch. During this Epoch 

 the ancestors of the human race must accordingly have 

 been represented, first by true Fishes, then by Mud-Fishes 

 (Bipneusta) and Amphibia, and finally by the oldest 

 Amnion Animals, the Protamnia. 



After the Palaeolithic Epoch comes a third main division 

 of the earth's organic history, known as the Mesolithic, or 

 Secondary Epoch. This is again distinguished into three 

 subdivisions — the Triassic, the Jurassic, and the Cretaceous 

 Periods. The approximate thickness of the strata-groups, 

 formed during these three Periods from the beginning of 

 the Triassic down to the end of the Cretaceous Period, 

 amounts in all to about 15,000 feet, not one half the thick- 

 ness of the Palaeolithic deposits. During this Epoch a very 

 great and varied development took place in all divisions of 

 the animal kingdom. In the vertebrate tribe especially a 

 number of new and interesting forms developed. Among 

 Fishes the Osseous Fishes (Teleostei) now first appear. But 

 the Reptiles surpass all others both in numbers and in 

 diversity of species — the most remarkable and the most 

 familiar forms being the gigantic extinct Dragons (Dino- 

 saurians), the Sea-Dragons (Halisaurians), and the Flying 

 Lizards (Pterosaurians). In reference to this predominance of 

 the reptilian class this time is known as the age of reptiles. 

 But the class of Birds also developed during this period, 

 undoubtedly originated from a branch of the lizard-like 

 Reptiles. This is shown by the similar embryology of Birds 

 and of Reptiles, by their Comparative Anatomy, and also by 

 the fact that we know of fossil birds with toothed ja^\s 



