GREGORY, THEORIES OF THE ORIGIN OF BIRDS 33 



Mr. Pycraft summed up this theory in his restoration entitled ''^One 

 of the '^Pro-Aves/ " This hypothetical animal, as thus represented, stands 

 about half way betAveen a normal lizard-like reptile on the one hand and 

 Archceopteryx on the other. It is represented as volplaning down from 

 the trees, with arms outstretched. It is covered with scales, which on the 

 back of the arm and sides of the tail have begun to lengthen out and 

 transform into feathers. 



The next year (1907) Baron Francis Nopcsa, in the Proceedings of 

 the Zoological Society of London,* after reviewing the many resemblances 

 between birds and running dinosaurs and showing that birds both in their 

 mode of flight and in their limb structure differ in many important re- 

 spects from bats, flying squirrels and other primarily tree-living animals 

 that are i)rovided with webs of skin for volplaning, came to the following 

 conclusions : 



"If we, after these preliminaries, now suppose that Birds, before at- 

 taining the ArcJiwopteryx-stsite, originated from quadrupedal arboreal 

 animals and only after having learnt to fly became bipedal, it is difficult 

 to understand why they in general show Dinosaurian affinities, why they 

 did not use both hind and fore limbs to the same extent for flight as they 

 would have done for arboreal locomotion, why the bones of the pectoral 

 region and of the wings show more primitive traces than the hind parts 

 of the body, and why they did not, like all other quadrupedal flying ani- 

 mals, develop a patagium ; whereas, if we consider that in Archwopteryx 

 the anterior extremities, though bearing the most important ectodermal 

 pinions, are less modified than the posterior extremities, which are al- 

 ready perfectly bird-like, and if we then suppose that Birds originated 

 from bipedal Dinosaur-like Reptiles, it is easy to understand what in- 

 duced the Birds to attain an Archceopteryx-like stage of evolution, for at 

 first a certain amount of bipedal, and only afterwards a volant, modifica- 

 tion would be required. 



"While we can safely state that a bipedal animal never could or did 

 develop a patagium without giving up bipedalism, this cannot be said of 

 feather-bearing forms, for we may quite well suppose that birds origi- 

 nated from bipedal Jong-tailed cursorial reptiles which during running 

 oared along in the air by flapping their free anterior extremities. . . . 

 A double running and flapping action would — somewhat in accordance 

 with Py craft's views on this subject — subsequently easily lead to an en- 

 largement of the posterior marginal scales of the antibrachium, and at 

 the same time produce a certain amoiuit of bipedal specialization. 



* "Ideas on the Origin of Fliglit." Proceedings of the Zoological Society of LondoQ, 

 June 12, 1907. 



