Animals Befwe Man 



Toward the close of the Cretaceous there 

 took place the most extensive upheaval that 

 has occurred on our continent, giving rise to- 

 the Wasatch, Uinta, and Rocky Mountain 

 ranges. The disturbance continued along the 

 " back - bone of the continent " and affected 

 South America as well, and it was accompanied 

 in places by the bursting open of the earth and 

 the outpouring of vast floods of lava. These 

 changes had a far-reaching and almost imme- 

 diate effect upon the life of the period. To 

 some extent this was probably direct, by de- 

 stroying many animals outright ; but the most 

 sweeping effects must ultimately have been due 

 to changes in climate and subsequent changes 

 in vegetation. 



"The disappearance of species at the close 

 of Mesozoic time was one of the most noted in 

 all geological history. Probably not a tenth 

 part of the animal species of the world disap- 

 peared at the time, . . . yet the change was so 

 comprehensive that no Cretaceous species of 

 vertebrate is yet known to occur in the rocks 

 of the American Tertiary, and not even a ma- 



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