DISTRIBUTIONAL PATTERNS OF VERTEBRATES 445 



this western element in Florida suggests past climatic fluctuations 

 on the coastal plain that favored eastward spread. This element 

 includes: Scaphiopus holbrooki, Bufo woodhousei, Microhyla caro- 

 linensis, Sceloporiis undidatus, Cnemidophorus sexlineatus, Crotalus 

 adamanteus, Speotyto cimicularia, Aphelocoma coerulescens, Pero- 

 myscus polionotus, P. gossypinns, Reithrodontomys humulis, R. 

 fulvescens, Geoniys pinetis, and Neotoma Jloridana. Some of these 

 (e.g., Microhyla carolinensis and Peromyscus gossypinus) have 

 become adapted to high-moisture situations of the coastal plain. 

 Others have tended to retain their xeric adaptations and exist today 

 in the most xeric situations available. The most extreme examples 

 of the latter group include Scaphiopus, Cnemidophorus, Aphelocoma, 

 and Peromyscus poliojiotus. 



Relictual Distributions in the Southern Grasslands 



Present relictual occurrences of forest plants and animals argue 

 against the past stability of the grasslands. The isolated populations 

 are reasonably assumed to be remnants of the widespread popula- 

 tions of post-Wisconsin time and indicate greater, or at least more 

 effective, moisture in the not distant past than prevails in the grass- 

 land today. The sugar maple group {Acer saccharum and others) is 

 an important example because it is representative of a group with 

 Mexican disjuncts that was regarded by Braun (1955) as having 

 been separated since pre-Pliocene times. Martin and Harrell (1957) 

 showed the occurrences of Acer skulchii in Mexico and Guatemala 

 and the general distribution of the saccharum group in the eastern 

 United States, but they overlooked a highly' significant group of 

 relictual populations in Texas and western Oklahoma, These are 

 shown in Fig. 4 along with an approximation of the western limits 

 of this group in the eastern forest and the approximate eastern limits 

 of the representative of this group (A . grandidentatum) in the south- 

 ern Rocky Mountain chain. In Oklahoma, these relicts occur in the 

 Wichita Mountains in the southwestern part of the state and in 

 Caddo Canyon, Caddo County. In Texas, there are relict popula- 

 tions along the southern escarpment of the Edwards Plateau (Sar- 

 gent, 1922). Sugar maples (identified as A. grandidentatum) occur in 

 moist ravines in the higher mountains of trans- Pecos Texas (Sargent, 

 1922, and author's observations). It does not seem possible that the 

 Oklahoma and Texas populations are relicts of a pre-Pliocene dis- 



