340 C. SCHUCHERT MARINE INVERTEBRATE FOSSIL FAUNAS 



aud yet to the east of this land, on the great continental island of Mada- 

 gascar, none of these mammals are present, hut here we meet with an 

 abmidance of half-monkeys almost unrepresented in Africa. In the same 

 way we know that in the North Pacific Ocean occur the fur-seals, while 

 elsewhere are found the coarser-haired forms. Again, it is to the western 

 Pacific that we go for nautilus, and to the Southern Hemisphere for 

 penguins. 



In our study of the causes that govern the geographic distribution of 

 land life, we soon learn that it is very largely the physical environment 

 of today that controls its localization. Temperature, moisture, and alti- 

 tude above sealevel are the greater factors in the present control of or- 

 ganic distribution. The animals of the plains are not commonly found 

 in the forests, while those of the mountains are often localized at eleva- 

 tions whose temperature is comparable with the latitudinal ones. Ly- 

 dekker says, in his well known "Geographical History of Mammals^" : 

 "An excellent instance of this is afforded by South America, where there 

 are the open grassy plains of the Argentine, the dense tropical forests of 

 Paraguay and Brazil, and the snow-clad heights of the Andes." Station 

 is therefore very intimately connected Avith temperature, and is well 

 illustrated by the distribution of the llama-like animals. ViciLhas and 

 guanacos occur in the high Andes of Peru and Ecuador, but as we go 

 farther south the guanaco only is found on the plains of southern Argen- 

 tina and Patagonia, as Avell as on the island of Tierra del Fuego, at the 

 sealevel. Being an animal which can live only in cold or temperate cli- 

 mates, it finds suitable conditions for its existence in tropical latitudes 

 solely at a height of many thousands of feet, although farther south it is 

 able to thrive at sealevel. 



While temi3erature and moisture are the present dominant controls in 

 the distribution of life, we learn from x'Vlfred Russel Wallace that when 

 an English naturalist is collecting in Japan "he sees so many familiar 

 natural objects that he can hardly help fancying he is close to his home.'' 

 And yet between the two countries there lies a continent with a wholly 

 dissimilar flora and fauna. In this we get a hint of an intermediate area 

 Avith a changed environment and a former continuous distribution of life 

 noAv more or less restricted to Avestern Europe and Japan. On the other 

 hand, when Roosevelt was hunting in east-central Africa he Avas con- 

 stantly reminded of the fact that the mammal Avorld there had its closest 

 relationship to those of other lands during- the Pliocene. From these 

 statements it appears that Avhile the present distribution of plants and 

 animals is largely controlled by temperature and moisture, yet back of 

 these factors lies the greater one of geographic migrations, AAdiich in turn 



