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homologous with those of the cursorial dinosaurs. It is therefore 

 argued that the origin of flight involved changes in the fore limbs only 

 and that the beginnings of flight occurred while running efficiency 

 was at its height. The conclusion is that the first birds arose from 

 some long-tailed reptile (Fig. 147) that sped over the earth on its 

 strong hind legs and stretched out its fore limbs for the sake of main- 

 taining balance and probably flapped these limbs to aid the speed of 

 flight. These flapping fore limbs, or pro-wings ; developed more sur- 

 face, partly by flattening out and partly by the backward growth of 

 the scales of the posterior margin. Similar large scales are supposed 

 to have developed laterally on the tail. The evolution of these spe- 

 cialized flight-scales into feathers is thought to have been a mere 

 matter of a continued increase in size and numbers, accompanied by 

 regional specialization; for in reality a feather is morphologically no 

 more nor less than a specialized scale. The gradual modification of the 

 remaining body scales into feathers would be the logical sequence 

 of events, and the long list of flight adaptations would appear as 

 correlated variations. The first steps in flying would be prolonged 

 leaps, aided by the flapping pro- wings; then short soaring flights 

 would be made, followed by longer flights accomplished by energetic 

 flapping of the wings alternating with periods of soaring. While 

 rather plausible in some ways tbe theory of the cursorial origin of 

 flight has not gained any generaMacceptance. 



The theory of the arboreal origin of flight has met with more 

 widespread approval. Two phases of this general theory have been 

 advanced : the pair- wing theory, and the four-wing theory. 



The " pair- wing !> theory is derived directly from a study of the 

 characters of Archceopteryx (Fig. 148, 1). The long clawed, prehensile, f 

 probably climbing wing-fingers of this ancestral bird point toward 

 an arboreal habitat. It is believed to have been not a true flyer, but 

 merely a soarer or glider, capable of only short passages from limb 

 to limb, or from tree to tree. The lack of any foundation for a flight 

 musculature argues against the possibility that the creature could have 

 taken any long flights in which propulsion by means of wings would be 

 necessary. 



The " four-wing " theory of Beebe is the most recent theory 

 dealing with the origin of flight. This author made the remarkable 

 discovery that vestigial flight feathers occur on the thighs of a number 

 of species of modern birds. Traces of similar feathers were found on 



