. The origin and evolution of life, on the theory of action, reaction and interaction of energy. hypotheses assign two phases to the origin of flight in birds: first, a primary terrestrial phase, during which the pecuUar characters of the hind limbs and feet were developed with their strong analogies to the bipedal feet of dinosaurs; second, a purely arboreal phase. It is believed by the adherents of both the two- FiG. 108. Theoretic Mode of Para-chute Flight of the PrimitiveBird. Based on the four-wing theory. AfterBeebe. wing and the four-wing theorythat following the arborealphase, in which
. The origin and evolution of life, on the theory of action, reaction and interaction of energy. hypotheses assign two phases to the origin of flight in birds: first, a primary terrestrial phase, during which the pecuUar characters of the hind limbs and feet were developed with their strong analogies to the bipedal feet of dinosaurs; second, a purely arboreal phase. It is believed by the adherents of both the two- FiG. 108. Theoretic Mode of Para-chute Flight of the PrimitiveBird. Based on the four-wing theory. AfterBeebe. wing and the four-wing theorythat following the arborealphase, in which the powers offlight were fully developed,there occurred among thestruthious birds, such as theostriches, a secondary terres-trial phase in which thepowers of flight were secon-darily lost and rapid cursoriallocomotion on the ground wassecondarily developed. Thisinterpretation of the foot andlimb structure associatedwith the loss of teeth, whichis characteristic of all the higher birds, will explain the closeanalogies which exist between the ostrich-like dinosaur Stru- FiG. 109. Restoration
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