434 W. F. BLAIR 



coastal plain and the bordering grasslands to the west, although the 

 argument applies equally to other species in eastern North America 

 not today limited to the coastal plain. Two major biotic formations 

 are involved. The Austroriparian forest extends with only minor 

 variance in climate, ecological dominants, and general aspect from 

 eastern Texas to the Atlantic coast. The southern grasslands border 

 the forest of the west. These grasslands, with beginnings in the late 

 Miocene and great development in the Pliocene (Clements and 

 Chaney, 1937) stand today as a barrier to the westward distribution 

 of many forest animals. 



I consider three major questions: 



1. What is the evidence in regard to Pleistocene climates in the 

 southern United States? Were the climatic changes sufficiently 

 drastic as to force the withdrawal of warmth-adapted coastal plain 

 animals into separate eastern (Floridian) and western (Mexican) 

 refuges? 



2. How effective were the grasslands as a Pleistocene barrier to 

 the southwestward withdrawal of warmth-adapted species into 

 Mexico? 



3. How do present distributions fit the hypothesized Pleistocene 



climatic changes? 



SOUTHERN CLIMATES IN THE PLEISTOCENE 



Evidence from various sources indicates major ecological changes 

 on the coastal plain in the Pleistocene, including far southward 

 shifting of northern plants and animals during stages of glaciation 

 in the north. Climatic implications from these shifts must rest on 

 the assumption that ecological requirements of living species and 

 genera do not differ significantly from those of their Pleistocene 

 progenitors. When single taxa are involved, this assumption some- 

 times may be of doubtful validity. When whole faunal or floral 

 assemblages are represented, little or no basis seems to remain for 

 questioning its validity. 



Plant Fossils 



Most of the scanty but highly significant evidence from plant 

 fossils has been reviewed by Deevey (1949, 1950). On the western 

 coastal plain, spruce {Picea) and fir {Abies) pollens have been found 

 at the base of bog deposits in Lee, Milam, and Robertson counties. 



