. Annals of the New York Academy of Sciences. Science. [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 ; In t
. Annals of the New York Academy of Sciences. Science. [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 ; 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 ; 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 pe
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