[Annals N. Y. Acad. Sci., Vol. XXVII, pp. 31-38. 4, May, 191^1 



THEOEIES OF THE OEIGIN 



By William K. Geegoey 



(Presented before the Academy, 13 December, 1915, in connection with' 



Mr. 0. W. Beebe's paper on "A Tetrapteryx Stage 



in the Ancestry of Birds") 



Comparative anatomists of tlie nineteenth century demonstrated that 

 birds, in the entire ground plan of their brain, skeleton, reproductive 

 organs and all other structures, as well as in their mode of development, 

 are '^glorified Reptiles," or '^feathered saurians." In this instance the 

 unanimous findings of comparative anatomy may be regarded as practi- 

 cally decisive. 



But while all authorities agree that the assumed very remote ancestors 

 of birds that lived in the Carboniferous and Permian periods of the 

 earth's history were very probably scaly, lizard-like reptiles, there is no 

 such unanimity regarding the structure and habits of the more imme- 

 diate ancestors of birds, during the ages when scales were gradually 

 transforming into feathers and the art of flying was still in its earliest 

 stages. Professor Osborn, in 1900, after reviewing the evidence for the 

 well-known view that birds and dinosaurs had been derived from a com- 

 mon ancestral stock that lived during the Permian period, said :^ "In the 

 origin of the birds we have to imagine, first, a terrestrial stage, in which 

 bipedal was gradually substituted for quadrupedal progression; it would 

 appear probable that the bipedal progression was first acquired during a 

 terrestrial stage because the foot of birds is primarily a walking, and not 

 a climbing, organ; second, a cursorial bipedal or, more probably, an 

 arboreal stage, in which both fore limb and tail enjoyed a change of 

 function contemporaneous with the acquisition of feathers." 



In 1906 Mr. W. P. Pycraft, of the British Museum, argued that^ in 

 the stage preceding Archceopteryx (the oldest known fossil bird, of the 

 Jurassic period) the ancestral birds probably lived in the trees, leaping 

 from branch to branch and from tree to tree. "In these movements," he 



1 Manuscript receiyed by the Editor 24 February, 1916, 



2 "Reconsideration of the Evidence for a Common Dinosaur- Avian Stem in the Per- 

 mian," The American Naturalist, Vol. XXXIV, No. 406. 1900. 



3 "The Origin of Birds," Knowledge and Scientific News. September, 1906, pp. 531-532. 



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