352 THE BIOLOGY OF BIRDS 



began. It seems quite safe to say that birds evolved from a 

 reptilian stock ; it seems reasonable to regard Ornithischian 

 Dinosaurs as not far off the pedigree of birds ; but beyond 

 these general statements very little can be said with security. 

 As is usual in regard to " big lifts " in organic evolution, v^^e 

 must frankly admit ignorance. We must, however, hold 

 firmly to the general idea, as Professor W. K. Parker ex- 

 pressed it, that birds began as " fevered representatives of 

 reptiles, progressing in the direction of greater and greater 

 constitutional activity." 



§ 5. Speculations 



(i) Some authorities, such as the Hungarian palae- 

 ontologist Nopcsa, have suggested that birds arose from 

 long-tailed, bipedal reptiles, which ran and leaped along the 

 ground, flapping their fore-limbs — broadened out posteriorly, 

 first by scales and eventually by feathers. 



(2) Other authorities, such as Osborn, have suggested 

 that birds arose from arboreal reptiles, which were in the 

 habit of parachuting or volplaning from tree to tree. As 

 feathers evolved and the breast muscles strengthened, the 

 more or less passive parachute became an active wing which 

 could be used to strike the air. This view receives support 

 from the analogy of bats, for it is practically certain that they 

 evolved from Insectivora, among which the aberrant Galeo- 

 pithecus shows a finely developed patagium or parachute. 



(c) Beebe has made the interesting suggestion that birds 

 passed through a " four- winged or Tetrapteryx " arboreal 

 stage when the legs bore backward-directed feathers like those 

 on the arms, both sets serving as parachutes for gliding. 

 There seem to be indications of tufts of feathers on the hind 

 limb of Archaeopteryx and of sprouting quills in the same 

 position on some newly hatched birds. 



(d) Dr. W. K. Gregory (1916) suggests a sort of com- 

 promise, and we must keep in mind the possibility that birds 

 had a dual origin, some from cursorial and others from 

 arboreal ancestors. " The pro-Aves were surely quick 



