374 ORIGIN OF LIFE IN AMEEICA 



explain their present range by a direct land bridge between 

 the two continents. The American ostrich (Rhea) is only 

 known fossil from superficial deposits, but the ostrich (Stru- 

 thio) occurs in the Miocene or Lower Pliocene of the Siwaliks 

 of India and of the island of Samos. Since the ostrich once 

 lived in the Mediterranean region, it is possible that the 

 common ancestor of the two families may have utilised the 

 mid-Atlantic land bridge to travel from the Old World to 

 the New or vice versa. 



The reptiles and amphibians, as Dr. Blanford * has pointed 

 out, indicate a much more pronounced faunal relationship 

 between South America and Africa than the birds or mammals 

 do. Professor Pf effer f endeavoured to explain this very inge- 

 niously by the assumption of a former sub-universal, or 

 almost universal, distribution and a subeeqnent extinction on 

 the northern continents. He admits that some form of 

 land bridge was necessary, of course, yet almost all inter- 

 continental communication must have passed, according 

 to his views, across a Bering Strait land bridge. He 

 quotes a number of instances of groups which are now 

 confined to the southern hemisphere, but have once also 

 extended to the northern continents, and because they 

 have done so he contends that they must have had a 

 sub-universal distribution. All those examples which are 

 not found fossil in the northern hemisphere are nevertheless 

 supposed to have had a similar range and to have gained their 

 present southern distribution in different countries by wander- 

 ing from one to the other almost by way of the North Pole and 

 then south again. Nothing but a careful general study of 

 existing distribution can convince us of the fallacy of such 

 an assumption. 



Let us take, for instance, the family of fresh-water tortoises, 

 the Pelomedusidae. It is confined to Africa, including Mada- 

 gascar, and South America. Curiously enough, one of the 

 genera of this family, viz., Podocnem'is at present inhabits 

 only northern South America and Madagascar. But, as Pro- 

 fessor Pfeffer tells us, the genus is known as far back as 



* Blanford, W. T., " Anniversary Address,'' pp.70 — 71. 



t Pfeffer, G., " Zoogeographische Beziehungen," pp. 417 — 418. 



