386 



PROGRESSIVE DEVELOPMENT 



Taumerics 



iws 



wrist 



co\v 



Hvcmerus 



and mingled. For example, American camels and horses may 



have migrated to Asia or vice versa. 



It was also known by 

 geologists that the Gobi 

 Desert, Mongolia, in Asia 

 was elevated from the sea 

 during the period of time 

 when reptiles were abun- 

 dant. It became dry 

 land at that time and 

 has remained dry ever 

 since. The American Mu- 

 seum of Natural History 

 financed expeditions, 

 headed by Roy Chapman 

 Andrews (see frontis- 

 piece), to Mongolia to 

 investigate the desert for 

 remains of reptiles. Since 

 reptiles were the prede- 

 cessors of man, it was 

 hoped that a transitional 

 form between the reptiles 

 and man, or between the 

 early mammals and man, 

 would be unearthed. 



There seems to be a common plan of structure in the 



limbs of various vertebrates which points to a common Because of climatic COn- 

 ancestor. . 



ditions, deserts are pecu- 

 liarly fitted to preserve fossils. Few people have penetrated and 

 lived in the desert, so fossils are more or less undisturbed. Asia 

 was thought to be a dispersal center to Europe on one side and 

 America on the other. These expeditions have met with the 

 greatest success in unearthing remains of reptiles and early 



