154 STRUCTURE AND CLASSIFICATION OF BIRDS 



the reptilian stem was at a time when the characters of the 

 amphibian had been incompletely thrown off, and at a time 

 also when the mammals diverged on their own path from a 

 point near to that whence the birds took their origin. The 

 general belief is in the origin of birds from some reptile stem, 

 but there is not an absolute agreement as to precisely which 

 group of reptiles birds are most nearly akin to. The researches 

 of Marsh and Huxley, besides those of Cope, Seeley, 

 Htjlkb, and some others, have led to a general acceptance of 

 a nearer kinship with the dinosaurs than with any other 

 group of reptiles. In considering the question, then, which 

 forms the subject of the present chapter, we shall commence 

 with the dinosaurs. The dinosaurs, ranging in size from 

 vast creatures of 70 or 80 feet in length to a diminutive reptile 

 half the size of the domestic fowl, are first known from 

 the Trias, persisted though the Jurassic and finally came to 

 an end in the Cretaceous epoch, later than which no 

 remains have been found. So far as we are aware birds 

 came into existence in the Jurassic period ; hence there is 

 no anachronism in considering them from the dinosaurian 

 aspect. 



It was formerly held that birds antedated the Jurassic 

 period ; for some of the celebrated tridactyle footprints in 

 the sandstone of the Triassic period were put down to birds. 

 It seems, however, to be now fairly certain that those foot- 

 prints are of dinosaurs. Still with so specialised a form as 

 Archceopteryx certainly was, and as Laopteryx probably was 

 in the Jura, it would not be surprising to meet with genuine 

 avian remains in the Trias. But even then there are 

 undoubtedly dinosaurs belonging to that period, so that the 

 question of relationship would resolve itself into a common 

 origin, not a derivation of birds from dinosaurs. 



The part of the skeleton in which most resemblance is 

 shown between birds and dinosaurs is the pelvis. The 

 dinosaurian pelvis consists of apparently three elements, like 

 that of birds, but the pubis is an L-shaped bone, constructed 

 of two pieces, one directed forwards and the other back- 

 wards and parallel with the ischium of its side. The latter 



