xm 



PHYLUM CH( )RDATA 



445 



peculiarities tliat the Ratita^ are distinguislied from the Cariuatai, 

 and there is every reason for thinkiiii;' that they also are the de- 

 scendants of rivinfj Birds, and tliat their distinctive characters — 

 absence of locking apparatus in the feathers, keel-less sternum, wide 

 coraco-scapular angle, &c. — are all due to degeneration correlated 

 with disuse of the wings. From the fact that the dromcuoraathous 

 skull is more reptilian than any other type, it would seem that the 

 Ratita' diverged early from the cariiiate stock. From the fact 

 that, in the structure of the skull and pelvis, the Ostrich and Rhea 

 are widely separated both from one another and from the Austral- 

 asian Ratita', it seems probable that the three orders of Ratitie 

 arose independently from primitive Carinata', and that the entire 

 division is to be looked upon as a convergent or pohjphyleLic group, 

 owing its distinctive characters, not to descent from a common 

 ancestor, but to the independent acquisition of similar characters 

 under the influence of like surroundings. 



The question of the phylogeny of the orders of Carinata3 is far too 

 complex to be discussed here. Suffice it to say that the Ichthy- 

 ornithes, Odontolca', Impennes, P3'gopodes, and Crypturi are to be 

 looked upon as the lowest or most generalised orders, while the 

 highest or most specialised are the Psittaci, the Accipitres, the 

 Striges, the Picarite, and especially the Passeres. Among the latter 

 the Corvida) (Crows) are probably the most exalted members of the 

 class (Fig. 1079). 



PASSERES 



COLYMBl XICHTHYOfmnHES 



ODONTOLCAE 



GALLINAE 



CRYPTURI 



MEGISTANES 



ARCHAEORNITHES 



ORNITHOSAURIA 



DINOSAURIA 



Fig. 1079.— Diagram illustrating the Relationships of the chief groups of Birds. 



