Early Development of Appendicular Skeleton of the Ostrich. 363 



better known it was felt that all the discovered forms were too 

 specialised to have been directly ancestral, and that it was more 

 likely that dinosaurs and birds had sprung from some common form. 

 Many went much further, and held that the resemblances between 

 birds and dinosaurs were purely adaptive, and did not indicate any 

 close affinity between the groups. Most of those who rejected the 

 view that dinosaurs and birds are related favoured the theory that 

 the avian ancestor was to be found among the pterosaurs. A few 

 even adopted the very remarkable view that carinate birds sprang 

 from pterosaurs and ratite birds from dinosaurs ! Fiirbringer in his 

 great work on birds (1888) concludes that birds are monophyletic, 

 and that the ancestral form was a sauropsidan lying intermediate 

 between the Dinosauria, Crocodilia, and Lacertilia. Osborn has 

 recently ably discussed the question, and comes to the conclusion 

 that " the avian phylum may have been given off from tho 

 dinosaurian," and that " the dinosaur-avian stem hypothesis 

 deserves to be very seriously reconsidered." 



The extremely close resemblance between the hind limb of the 

 bird and the carnivorous dinosaur is admitted by all, and the 

 question to be decided is whether the bird could have evolved an 

 almost identical mechanism from an undifferentiated primitive type 

 such as is seen in Palceohatteria. The formation of a tibio-tarsus, 

 by which a loose joint is converted into a firm joint, has pretty 

 clearly arisen in connection with the support of the body on the 

 hind limbs. In the case of the carnivorous dinosaur the stages of 

 the formation are pretty clearly seen. Did the bipedal progression 

 of the bird give rise to a dinosaur-like arrangement after the 

 development of feathers or before ? In the primitive bird Archceo- 

 pteryx a tibio-tarsus and a tarso- metatarsus are already formed. But 

 though Archceopteryx doubtless perched on its hind feet, it is not 

 likely to have gone in for very much bipedal progression, and for 

 both its climbing among the branches of trees and for perching the 

 primitive type of tarsus would probably have amply served. The 

 phalangers, lemurs, and many other mammals are probably quite as 

 expert climbers as ever was Archceopteryx, and yet they have never 

 evolved anything analogous to a tibio-tarsus or a fusion of the meta- 

 tarsals, and with them the distal tarsal elements. The chameleon 

 has a much better grasping foot than any bird, but the tarsus is not 

 at all modified on bird-like lines. And it is clear that it is not the 

 later typical bipedal progression of the bird that has evolved the 

 tibio-tarsus, for it is as typically developed in Archceopteryx. If the 

 habits of the primitive bird are not likely to have given rise to the 

 typical avian mechanism, we seem to be forced to the conclusion that 



