3 2o THE ANIMALS OF THE ANTARCTIC 



occurring in certain fossil penguins (Palct'ospheniseus and Paraptenodytes) from 

 strata of later Tertiary age in Patagonia. Yet more important is the greater 

 relative length and slenderness of the shank-bone of the leg in the Sej^mour 

 Island penguin as compared with its modern representatives, in which this portion 

 of the skeleton differs remarkably from that of all other birds. The three 

 elements of which this bone is composed are also more completely welded together 

 than in living penguins. This points to the conclusion that penguins are 

 descended from birds endowed with the power of flight, the shortening and 

 expansion of the shank-bones being due to the lack of active use of the hind-limbs, 

 which are required merely as firm bases of support, and as a rudder in swimming. 

 The nearest relatives of penguins are apparently divers and petrels. 



