68 



THE WHITE RIVER BADLANDS 



The distribution of animals is closely related to their 

 development and has been in large measure controlled by 

 geographical conditions. A study of paleogeography shows 

 that the several continents have had a varied career. 

 Changes have taken place in them through all the ages and 

 migration roads and barriers, in long procession, have 



Figure 18 — Land areas of the world during Miocene time. A period 

 of continental elevation and emergence, consequently of re- 

 newed land connections and migrations. Africa broadly united 

 with Europe across the Arabic peninsula, and a typical Asiatic 

 fauna roaming westward into Europe and Africa. Asia connect- 

 ed with the East Indies and the Philippine Islands. Florida 

 elevated at the close of the Miocene. South America divided into 

 northern and southern halves by a broad gulf, the northern half 

 perhaps connected with North America. Australia entirely sep- 

 arated from Asia. Rearranged after W. D. Matthew, 1908. H. 

 F. Osborn: The Age of Mammals in Europe, Asia and North 

 America, 1910. Published by The Macmillan Company. Re- 

 printed by permission. 



formed and disappeared. With the advent of mammalian 

 life interest in these physiographic changes increases and 

 their interpretation is made with greater assurance of 

 accuracy. 



Life in the older geologic time was simple. The forms 

 increased in complexity as the ages came and passed. Primi- 

 tive mammals appeared during the Mesozoic but not until the 



