DISTRIBUTIONAL PATTERNS OF VERTEBRATES 465 



The fossil evidence of ecological change in the southern United 

 States during the Pleistocene and the evidence derived from the 

 existing distributional patterns of vertebrates are consistent in 

 indicating that the east-west splitting of the warm-adapted biota 

 by the southward shift of colder climates and of the cold-adapted 

 biotas has been the chief agency initiating speciation in this area. 

 The urodeles of the eastern United States show very different dis- 

 tributional patterns from the anurans, because the conditions that 

 fragmented the ranges of the warmth-adapted anurans promoted 

 the southward and westward spread of the urodeles. Then, the condi- 

 tions that permitted reoccupation of the coastal plain by the anurans 

 would have forced northward and eastward the retreat of the 

 urodeles. 



Acknowledgment 



Base map for figures used with permission of University of Chicago. 

 Base map for Figs. 1, 2, and 6, copyright 1937 by the University of 

 Chicago. Base map used for Figs. 3, 4, 5, 7, 9, and 10, copyright 1938 by 

 the University of Chicago. 



REFERENCES 



Adams, Charles C. 1902. Southeastern United States as a center of 



geographical distribution of flora and fauna. Biol. Bull., 3: 115-131. 

 Allen, Glover M. 1930. The walrus in New England. /. Mammal., 11: 



139-145. 

 Baker, C. L. 1947. The species of amphiumae. /. Tenn. Acad. Sci., 22: 



9-21. 

 Berry, E. W. 1907. Pleistocene plants from Alabama. Am. Naturalist, 41: 



689-690. 

 Blair, Albert P. 1941. Variation, isolation mechanisms and hybridization 



in certain roads. Genetics, 26: 398-417. 

 Blair, W. Frank. 1939. Faunal relationships and geographic distribution 



of mammals in Oklahoma. Am. Midland Naturalist, 22: 85-133. 

 . 1943. Biological and morphological distinctness of a previously 



undescribed species of the Peromyscus tniei group from Texas. 



Contribs. Lab. Vert. Biol., Univ. Mich. 24: 1-8. 

 . 1950. Ecological factors in speciation of Peromyscus. Evolution, 



4: 253-275. 

 . 1951. Interbreeding of natural populations of vertebrates. 



Am. Naturalist, 85: 9-30. 

 . 1952. Mammals of the Tamaulipan biotic province in Texas. 



Texas J. Sci., 4: 230-250. 

 . 1954. Mammals of the mesquite plains biotic district in Texas 



