540 LIFE AS RELATED TO PHYSICAL CONDITIONS 



not necessarily the only ones suited to it ; animals from 

 other places may be even better adapted, but they have 

 been kept out by some natural barrier. This is particu- 

 larly evident in the case of Australia, where the weak native 

 animals would have been readily displaced by the stronger 

 animals of Asia could these have reached that isolated con- 

 tinent. 



Life on Islands. Islands which rise from the conti- 

 nental shelves were probably at one time connected with 

 the continents, but have since been separated by the sub- 

 mergence of the intervening lowland. The animals and 

 plants of such islands are similar to those of the adjacent 



large land masses. But oceanic 

 islands possess only those types 

 of plants and animals which 

 originally were able to float or 

 fly to them over the surround- 

 ing water expanse. Indigenous 

 mammals, except certain species 

 of bat, are wanting. Birds are 

 abundant. 



On the tropical islands the 

 cocoanut palm furnishes the main 

 supply of vegetable food, cloth- 

 ing, and building material. Many of the species of both 

 plants and animals are different from those of the nearest 

 continent and even of the adjacent islands. So complete 

 has been the isolation of the life on these islands for so long 

 a time that it has been possible for great differences in 

 species to develop. Large unwieldy birds unable to fly or 

 run rapidly have been found on some oceanic islands, the 



THE DODO 



Although the dodo is extinct, 

 sufficient remains have been 

 found to enable scientists to 

 tell how it looked. 



