THE PROGRESS OF LIFE 89 



Eocene, but insects were not abundant before the 

 Oligocene. Sea-snakes occur in the Eocene, and land 

 tortoises in the Miocene. The great development of 

 birds was very remarkable ; for remains of all the 

 existing orders of Carinatse have been found in the 

 Oligocene, except divers, gulls, pigeons, and parrots ; 

 and these are recorded from the Miocene. All the 

 Miocene and many of the Oligocene birds appear to 

 belong to genera still existing. 



Of the mammalia the multituberculata died out 

 in the Cainozoic (Miocene ?) of Patagonia. The 

 metatheria are represented in the Eocene of the 

 northern hemisphere by several forms of polyprotodont 

 marsupials ; but they were quite overshadowed by the 

 eutheria. It was in the southern hemisphere that the 

 marsupials flourished, and gave rise to the diprotodont 

 section, which is known only from Australia and 

 South America. The eutheria, or placental mammals, 

 suddenly appear in abundance in the lower Eocene ; 

 and, before the close of that period, most of the 

 existing orders were represented, as well as some sub- 

 orders which are now extinct. In the Oligocene we 

 find some existing genera, and many more in the 

 Miocene. The extinct sub-orders are chiefly from 

 North America, and are generalised groups connecting 

 the existing orders. They had very small brains and 

 smooth bones without ridges ; all had five toes on each 

 foot, and their molar teeth were trituberculate. 



The Eocene Creodonta are the primitive Carnivora ; 

 but they had no canine teeth, and in their dentition 

 they are related to both the Insectivora and the 

 polyprotodont marsupials. With them were the 

 Condylartlim, the early ungulate or hoofed mammals, 



