3fi ANNALfi NEW YORK ACADEMY OF f^ClENCEH 



Beebe found that in the young of various species of doves, pigeons, 

 jacanas and owls there is a reduced pelvic wing, consisting of a row of 

 degenerate flight feathers and a second overlapping row of "^'coverts," all 

 stretched upon the patagium, or skin-fold, behind the femur. Owing to 

 the lateness of the season, it was impossible at this time to extend further 

 his observations on the '^pelvic wing" of birds; but he states that "judging 

 merely from the pterylosis of the adult, many species of Coraciiformes, 

 Scansores and Piciformes should show most interesting developments of 

 this tract in the young birds." Mr. Beebe was naturally delighted to 

 find that in the Berlin specimen of ArchcEopteryx there were some 

 strongly marked impressions of feathers on both sides of the tibia and of 

 still larger feathers lying between the pelvis and the bent back head, 

 which he interprets as evidence of the "pelvic wing" in this oldest known 

 bird. Partly from these data Mr. Beebe and Mr. Dwight Franklin have 

 made their series of restorations to illustrate the evolution of birds from 

 a "tetrapteryx stage," with four wings and a long segmental tail, to the 

 modernized two-Avinged stage, with a normal fan-tail. 



Thus Mr. Beebe, along with Pycraft, Abel and others, conceives the 

 immediate ancestors of birds as arboreal animals with the habit of scaling 

 doAvnwards through the air after the fashion of flying squirrels; to this 

 theory his discovery of a vestigial pelvic wing in modern birds lends 

 obvious support. 



For some years past the present writer has taken special interest in the 

 problem of the origin of birds, partly for the reason that the subject 

 forms one of the major problems in the Columbia University graduate 

 course on the evolution of the vertebrates. Each year we hold a seminar 

 on this subject, in which the various theories of the origin of the birds 

 are duly advocated by graduate students, and the rival claims of the dino- 

 saurs and other reptilian groups to close kinship with the birds are con- 

 sidered. From this annual review arises the impression that from the 

 clash of conflicting hypotheses the following approximation to the facts 

 may, from present evidence, be provisionally made out : 



Far back in the Carboniferous ages the remote common ancestors of 

 birds, dinosaurs, pterosaurs and other reptilian groups were very primi- 

 tive lizard-like reptiles with extremely small brains, comparatively slug- 

 gish habits and a highly variable body temperature. This general de- 

 scription would doubtless fit many of the alr(3ady known 'reptiles from 

 the Carboniferous and Permian, but no one of these can yet be recognized 

 as a direct ancestor to the later types. 



In the harsh arid ages of the Permian and Trias were evolved hardier 

 and more active carnivorous saurians, represented by the earliest dino- 



