A HISTORY Of VERTEBRATES: BIRDS AND MAMMALS 481 



of the jaws of Ichthyornis, which was a tern-sized, flying species, is uncer- 

 tain. Marsh, who described it in 1880, considered that a toothed lower 

 jaw, which was found in close association with the rest of the fossil, 

 belonged to it. More recently, Gregory has identified the lower jaw as 

 belonging to a small marine lizard. Although they are placed in the 

 subclass Neornithes along with modern birds, the more primitive nature 

 of these Cretaceous species is recognized by placing them in a distinct 

 superorder— the Odontognathae. 



All later birds have lost the reptilian teeth, but a few (superorder 

 Palaeognathae) retain a somewhat reptilian palate, whereas others (sub- 

 order Neognathae) have a more specialized palatal structure. Living 

 paleognathous birds are for the most part ground-dwelling, flightless 

 species, such as the ostriches of Africa, the rheas of South America, the 

 cassowaries of Australia and the peculiar kiwi of New Zealand (Fig. 

 24.8). The legs are well developed and powerful, the wings vestigial, and 

 the feathers do not have booklets. Presumably these birds evolved from 

 flying ancestors, but readapted to a terrestrial mode of life in areas where 

 there was an abundant food supply upon the ground and few com- 

 petitors or enemies. The ancestry of certain of them can be traced back 

 to the early Cenozoic era. A number of large, ground-dwelling neognath- 

 ous birds also lived then, which suggests that there might have been a 

 competition at this time between birds and early mammals for the 

 conquest of the land surface, which had recently, geologically speaking, 

 been vacated by the large reptiles. Mammals won, and only a few 

 ground-dwelling birds survived. 



All other birds, including the vast majority of living species, are 

 neognathous types. They have been very successful and have adapted to 

 numerous habitats and modes of life (Fig. 24.9). Some, including the 

 loons, ducks and gulls, are aquatic as well as good fliers. Other aquatic 

 species, such as the penguins, have lost their ability to fly, and their 

 wings are modified as paddles for swimming under water. The herons, 

 cranes and coots have become specialized for a wading, marsh-dwelling 

 mode of life. Hawks, eagles and owls are birds of prey. The grouse, 

 pheasants and fowl are predominantly terrestrial forms, though they can 

 fly short distances, and the song and perching birds are well adapted for 

 life in the trees. Twenty-three orders of neognathous birds are recog- 

 nized (cf. appendix). The song birds are members of the order Pas- 

 seriformes. 



210. The Bird Way of Life 



Man has learned more about the habits of birds and their way of 

 life than about most members of other classes, for he has long been 

 fascinated by these colorful creatures that lead such intense and active 

 lives. A few of their more interesting features are considered below. 



Food Geii'ing. Birds have a high rate of metabolism and must 

 obtain large quantities of food to support it. During most of their 

 waking hours they are on the look-out for seeds, insects, worms, or what- 

 ever makes up their diet. Crows and some other birds eat a variety of 



