ON THE ORiaiN OF FLIGHT IN BIRDS. 463 



25. On the Origin o£ Flight in Birds. 

 By Baron Feancis Noposa. 



[Received April 24, 1923 : Bead April 24, 1923.] 



(Text-figures 1-7.) 



In 1907 I bi"ought forward the idea that birds originated from 

 bipedal Dinosaur-like running reptiles in which the anterior ex- 

 tremities, on account of flapping movements, had gradually turned 

 to wings without thereby afiecting terrestrial locomotion (14). 

 This idea has been on several occasions criticised by various 

 authors (1, 3, 9, 12, 16). 



In consequence of new material having turned up that has some 

 bearing on this subject, the time seems to have arrived when 

 the dillerent ci-iticisms to which the hypothesis of a " running 

 Proavis" has been subjected can be reviewed. 



The first criticism was brought forward by Hay (9), who dis- 

 agreed with my idea on account of my having drawn Proavis 

 with too short arms and with a reduced and rotated hallux. 

 According to Hay's view, birds never could have originated from 

 such a form unless considerable rejuvenation might be presumed. 

 The Dinosaurs Hay supposes to have been originally quadru- 

 pedal. 



, Hay's view was endorsed by Abel (1), who, on account of 

 the rotation of the hallux and the development of a prehensile 

 manus in Archfjeopteryx and Dinosaurs, in 1912 supported the 

 idea that both birds and Dinosaurs were derived from arboi-eal 

 forms. Steiner tried to derive arguments against my hypo- 

 thesis from the diastaxic arrangement of the feathers, the origin 

 of which he traced back to some arboreal Agamid (16). In a later 

 paper (17) he likewise emphasised the prehensile structure of the 

 manus in primitive birds, but at the same time he believed that 

 Abel's arguments, based on hallux and pollex, were devoid of 

 foundation. 



Beebe (3) and Lucas (12) fully appreciate the difficulty that 

 arises from the fact that, while in all arboricolous passive fliers the 

 centre of the parachute surface coincides, as it must, with the 

 centre of gravity of the animal, this could not have been the case 

 in a primitive arboricolous bird having feathers only on its tail and 

 arms. They think to ovei-come this difficulty by assuming that 

 the most primitive arboreal birds had quills also on their legs. 



This stage in avian evolution Beebe terms the Tetrapteryx 

 stage ; and in support of his hypothesis, he falls back on the 

 observation that temporarily quills develop on the legs of several 

 kinds of birds, and are later replaced by down. 



