EVOLUTION AS SEEN IN THE STRUCTURE OF MODERN ANIMALS 



27 



ARBOREAL 

 Climbing 



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AERIAL 



Fl^yinc) 



TERRESTRIAL 

 Short, pentoidoicfyl 

 limbs 



CURSORIAL 

 Running 



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AQUATIC 

 Swimming 



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FOSSORIAL 



Burrowing 



FIG. 3.4. Adaptive radiation in limb structure of mammals. {Modified after Lull, Organic 

 Evolufion, The Macmillan Company, 1947.) 



representatives of them. Mammals possessing this primitive limb structure 

 are placed in the center of the diagram. Of the lines radiating from this 

 central point one leads to arboreal, a term for tree-dwelling forms, which 

 in one way or another have adapted limbs for life in trees; squirrels, 

 sloths, monkeys are among the examples. Another line leads to aerial, 

 representing mammals adapted for flight. Only bats occupy the position 

 at the terminus of this line, since they are the only truly flying mammals. 



