GEOGRAPHIC DISTRIBUTION OF ANIMALS: CONTINENTS 



271 



lateral digits have been lost; i.e., no "splint bones" are present as they are 

 in the horse (p. 23). The digits of the one-humped Arabian camel spread 

 widely, offering effective support on soft desert sands. The feet of the two- 

 humped Bactrian camel of central Asia, as well as those of the llama, are 

 harder and less spreading, adapted for firmer and rockier terrain. 



Camels and their South American relatives have a highly discontinuous 

 distribution (Fig. 12.5 ) . As shown by the solid black areas of the map, true 



Tertiary A.ncesfr 

 of the Cam^li^ae. 



\Came/s 

 in 

 ■■'FUocene. 



No CarneTictiEt^ 

 until Pleistocene. 



FIG. 12.5. Geographic distribution of the Camelidoe (camels, llamas, etc.). Present range 

 shown in solid black; range during Pleistocene shown by diagonal lines. Arrows radiate 

 from center of dispersal. (From Matthew, Climafe and Evolution, Special Publications 

 of New York Academy of Sciences, Vol. I, 1939, p. 76.) 



camels inhabit Africa, to the southern edge of the Sahara desert, Arabia, 

 and the highlands of Asia. Llamas and their relatives inhabit the high- 

 lands of South America. The discontinuity between these ranges is almost 

 as great as that between the two parts of the range of tapirs. As in the case 

 of the latter, the explanation of the situation becomes evident when the fos- 

 sil record is consulted. During Pleistocene times camels ranged over North 

 and South America, Northern Africa, and most of Asia. Apparently they 

 first reached the Old World in the Pliocene but did not reach South Amer- 



