.7 



Origin and Affinities of the Present Western North 

 American Reptile and Amphibian Fauna 



Robert C. Stebbins 



Museum of Vertebrate Zoology, 

 University of California, Berkeley 



ABSTRACT 



1 he present distribution of amphibians and 

 reptiles in western North America suggests a comparatively recent 

 (geologically speaking) trend toward widespread increasing aridity. 

 This trend has been especially potent in affecting the course of 

 evolution and distribution in the more sedentary, moisture-depend- 

 ent species. Examples are presented from among the major groups 

 of amphibians and reptiles. 



The origin and affinities of the present salamander fauna of the 

 West are discussed. 



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