RODENTS OF LIBYA 49 



climatic regimen. At present, the Sahara Desert provides a decided 

 deterrent to nondesert rodents, and local barriers even prevent the 

 movements of desert rodents. Certainly, this was not the case through- 

 out much of the Pleistocene. 



From the above discussion it becomes evident that the climate of 

 the Sahara during the Pleistocene, although somewhat arid, fluctuated 

 in relation to climatic changes resulting from successive pluvial and 

 interpluvial periods. During the moist pluvial periods, rodents now 

 characteristic of the African veldt and savanna were able to disperse 

 northward. Conversely, during the dry interpluvials, rodents of the 

 steppes and deserts extended their ranges into the subtropical and 

 tropical regions of Africa. The present distribution and composition 

 of the African rodent fauna are probably a direct result of this inter- 

 mingling and interdigitation of populations during Pleistocene time. 

 The present widespread distribution in Africa of the gerbils (Ger- 

 billus) and spiny mice (Acomys), which are both restricted to arid 

 habitats, probably is the result of widespread shifting of mammalian 

 faunas during the dry interglacial periods. During interpluvials, 

 various arid regions in Africa, now disjunct and separated by inter- 

 vening areas of veldt and savanna or even tropical rain forest, probably 

 were continuous and would have permitted genetic interchange 

 among populations of gerbils that had previously been separated. 



Unfortunately the fossil record of African rodents is meager, and 

 many of the conclusions regarding distributional patterns of the 

 Libyan and Saharan Pleistocene rodent faunas are conjectural. It 

 seems reasonable to assume that at some period during the Pleisto- 

 cene, the central and southern African rodent fauna, exclusive of 

 that of the Congo Basin, dispersed far northward, probably to the 

 northern limits of the continent. 



Several extant species provide almost incontestable evidence of 

 this widespread, northward displacement of this rodent fauna. The 

 Barbary ground squirrel, AUantoxerus getulus Linnaeus, and the 

 Barbary striped mouse, Lemniscomys barbarus Linnaeus, of northern 

 Morocco and Algeria clearly represent residual populations of the 

 central African rodent fauna that advanced to the northern limits of 

 the continent during a Pleistocene pluvial. Both of these species have 

 all of their affinities with rodents occurring south of the Sahara. 

 Lemniscomys barbarus is considered by some to be conspecific with 

 populations of Lemniscomys Trouessart as far away as East Africa, 

 and AUantoxerus getulus is the only sciurid in North Africa; the 

 nearest other African squirrels occur south of the Sahara. 



In early Pleistocene times there were supposed broad land connec- 

 tions between Europe and North Africa and during the later Pleisto- 

 cene, there were periodic fluctuations of sea levels occasioned by the 



