686 



COLLEGE ZOOLOGY 



The Cenozoic Era is called the " Age of Mammals," since this 

 interval of about three million years, between the Mesozoic Era 

 and the present time, witnessed the ascendency of mammals and 

 the inauguration of their dominance over all other animals. The 

 mammalian characteristics of the periods in the Cenozoic Era 

 may be outlined briefly as follows (Osborn) : 



The Eocene is " characterized by the first appearance of many 

 of the ancestors of the modernized mammals and the gradual dis- 

 appearance of many of the archaic types characteristic of the Age 

 of Reptiles " (Mesozoic Era). 



The Oligocene is " characterized by the appearance of many 

 existing types of mammals and the gradual disappearance of 



many of the older 

 types." 



The Miocene is 

 an early stage of 

 modernization, 

 " in which lived 

 many mammals 

 closely similar to 

 existing forms.' 



The Pliocene 

 witnessed " a vast 



modernization of the mammals in which all the existing orders 

 and families are known, as well as many of the existing genera, 

 but few or no existing species." 



The Pleistocene is " a life period in which the majority of the 

 recent forms of mammals appear and in w r hich there occurs the 

 last glacial period and a great natural extinction of earlier forms 

 in all parts of the world." 



The Holocene, or recent time, is " characterized by the world- 

 wide destruction and elimination of mammals through the agency 

 of man." 



Among the fossil mammals found in North America are the 

 archaic ungulate, Uintatherium mirabile (Fig. 548), which was 



FIG. 548. Skeleton of Uintatherium mirabile. 

 (From Flower and Lydekker, after Marsh.) 



