AVES 291 



have been chosen. As a rule when the choice has lain between a 

 native and a foreign type the native type has been given the prefer- 

 ence. 



Toothed Flying Birds (Ichthyornithiformes) 



This order is represented by the single extinct genus Ichthyornis 

 (Fig. 155), several species of which have been found in Cretaceous 

 strata. These birds were evidently rather gull-like divers, if one may 

 judge by structure, but differed from all modern carinate birds in that 

 they had true teeth in sockets. Were it not that they are distinctly 

 keeled or flying birds they might appropriately have been placed, as 

 Knowlton places them, in the order with the toothed diving birds of 

 even earlier times. 



The Penguins (Spheniscifobmes) 



These curious, highly specialized, marine diving birds (Fig. 156, B), 

 have a wide distribution among the Antarctic Seas. They are really 

 flightless birds and might on that account be excluded from the Car- 

 inatse, but they have well-developed wings and a fairly good keel to 

 the sternum, the wings being used for "flying" through the water 

 instead of through the air; for the wings and not the feet are the 

 chief organs of locomotion; a unique character among diving birds. 

 The legs of the penguin are set so far back on the trunk that in the 

 water they are used primarily as a rudder, and on land their terminal 

 position makes the bird practically sit upright on the tail. The wings 

 are modified into flippers not unlike those of the whale; they are quite 

 devoid of flight feathers and the bony framework is quite stiff and 

 inflexible. The swimming stroke, when under the water, consists of 

 alternating rotary sweeps of the two flipper-like wings, which drive 

 the pointed body through the water at a fine speed. Penguins live 

 on fish, mollusks, and crustaceans. They are markedly gregarious, 

 especially during the breeding season, thousands of them being con- 

 gregated upon the narrow confines of rocky islets and points of land 

 along the sea shores. From various elevations they are constantly 

 diving into the icy water after their food, emerging wet and glistening, 

 but capable of almost instantly drjdng their plumage by vigorous 

 shaking of the muscular skin. The penguins and the screamers are 

 the only birds that have the skin completely covered with feathers. 

 In the penguins the feathers are lance-shaped and have flattened 



