442 W. F. BLAIR 



They probably did so along a cool savanna or open woodland 

 corridor." 



The question of past conditions in the area occupied by the south- 

 ern grasslands is highly germane to the problem of Pleistocene dis- 

 junctions in the southern United States. Most of the evidence 

 pertinent to this problem has never been summarized. It involves 

 Pleistocene fossils and present relictual distributions. The specific 

 question is one of how permanent has been the arid grassland 

 barrier. 



Invasion from South America 



Several South American groups of mammals crossed the supposed 

 grassland barrier and the coastal plain in the Pleistocene. Their 

 arrival in North America must have followed the development of 

 the Central American land bridge in the late Pliocene and early 

 Pleistocene, and their dispersal around the Gulf of Mexico and east- 

 ward across the coastal plain must have occurred after the develop- 

 ment of the presumed grassland barrier. The known Pleistocene 

 faunas of Florida include several representatives of this element, 

 including: the common porcupine (Erethizon dorsatum), capybaras 

 (two genera, Hydrochoerus and Neochoeriis), glyptodonts {Boreo- 

 stracon), armadillos {Daspyus, Holmesina), and ground sloths 

 {Megatherium, Megalonyx, Paraniylodon, Thinobadistes) , as listed by 

 Sherman (1952). Of these, the porcupine and ground sloths must 

 have required trees for their dispersal, and others, the capybaras, at 

 least, would have required much greater moisture than is available 

 at present in the southern grasslands. 



Fossil Evidence of Interglacial Conditions 



Various Pleistocene fossils from the region of the present grass- 

 lands represent groups that probably could not exist there under 

 present conditions and that probably required greater moisture or 

 forest. One of the most striking of these is the water rat (Neofiber). 

 At present this rodent is limited to bog situations in peninsular 

 Florida (Fig. 3). In what was probably the Third Interglacial 

 (Sangamon) this water rat occurred in the Texas panhandle and in 

 central Kansas (Meade, 1952; Hibbard, 1943). This rodent is also 

 known from the Pleistocene of Pennsylvania (Hibbard, 1955c), 

 where it presumably lived during an Interglacial interval. Another 



