3 



Distribution of Mammals in the 

 Pacific Area 



The reason for the presence of certain kinds of mammals 

 on one island group, for their absence from another, or the 

 substitution of still other kinds of animals on a third island, 

 must be sought in the interweaving histories of the evolution 

 of the mammals themselves and in the evolution of the topogra- 

 phy, climate, vegetation, and other components of their en- 

 vironments. 



ORIGIN AND EVOLUTION OF MAMMALS 



The earliest, most primitive mammals are lineal descendants 

 of peculiar reptile-like creatures whose fossil remains have been 

 found in South Africa and elsewhere. Those first mammals im- 

 perceptibly and during the course of very many generations 

 developed away from being actual reptiles. Gradually those 

 basic distinctions by which every mammal today is distinguished 

 from every reptile took form: heat-conserving and regulating 

 mechanisms including hair, sweat glands, special automatic 

 nervous control of the oxidizing processes were progressively 

 developed; milk glands, together with the change from egg- 

 laying to bearing of young, were evolved ; alterations took place 

 in the forms and functions of certain bones and muscles ad- 

 joining the head and the hinged part of the jaw. During an im- 

 mensely long period of time these alterations of body parts into 

 different shapes and for new purposes took place ; the descen- 

 dants of reptiles became mammals. 



Those dawn mammals were unlike any living mammals today. 



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