530 



The Earth and Its hihabitaiits Change 



UNIT X 



Desert or in Wyoming M'here dinosaurs 

 used to live. Then large expeditions are 

 equipped for exploring them. Sometimes 

 the bones of one animal arc all found to- 

 gether; more often they have been shifted 

 in position so that they are widely scat- 

 tered; many are much broken or com- 

 pletely lost. Digging out and later trans- 

 porting the petrified and often fragile 

 fragments of bone is a task requiring 

 training and skill. Later, in the labora- 

 tory, the bones are examined by experts 

 and assembled. Missinor bones are re- 

 placed by models and thus whole skele- 

 tons are reconstructed. 



Fig. 481 (above) Much work re'iiiahis to be 

 done after an expedition. Only experts can iden- 

 tify and piece together the fossil fragments sent 



home. (AMERICAN MUSEUM OF NATURAL HISTORY) 



Fig. 482 (left) An assistant is helping the sci- 

 entist to cover up gigantic bones with Inirlap 

 and flour paste for shipiiient. Large bones must 

 he careftilly protected. (American museum of 



NATURAL history) 



We learn much from a study of fossils. 

 Not only has the earth changed through- 

 out the ages but fossils indicate that the 

 inhabitants of the earth have changed, 

 too. There are no longer any mammoths, 

 saber-toothed tigers, or dinosaurs. Many 

 other kinds of plants and animals have 

 died out, become extinct. Furthermore, 

 existing animals and plants are almost al- 

 ways different from the animals and 

 plants of former ages. The changes were 

 so slow that they become evident only 

 as we look back millions of years. And 

 there is every reason to believe that 

 changes continue to go on. 



