SOUTH DAKOTA SCHOOL OF MINES 



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Cenozoic did they reach importance. They then became the 

 ruling type and the Cenozoic, for this reason is often called 

 The Age of Mammals. ( See Plate 9 ) . 



In early Tertiary time North America was apparently 

 not connected by land with South America. It was, how- 

 ever, connected with Asia by way of Alaska and with 

 Europe by way of Greenland and Iceland. These land 

 bridges and the Panama region are known to have changed 

 greatly during and subsequent to the Tertiary and a fair 

 understanding of their influence will explain many per- 

 plexing features of animal and plant distribution. 



Figure 19 — Land areas of the world during Pliocene time. A period 

 of continued continental elevation especially in Europe and East- 

 ern North America. Seasons of aridity or summer drought, in- 

 creased aridity of the Great Plains of North America. South 

 America connected with North America by migration routes 

 which allowed free interchange of mammals. Australia still 

 united with New Guinea and Tasmania. Rearranged after Mat- 

 thew, 1909. H. F. Osborn. The Age of Mammals in Europe, 

 Asia and North America, 1910. Published by The Macmillan 

 Company. Reprinted by permission. 



