In this article we will discuss about the origin of feathers and flights of birds.
Origin of Feathers and Flight Feathers:
Many authors are unanimous that feathers are transformed reptilian scales. Primary function of feather is insulation, while flight is only secondary, which is well documented in the ratite.
Flight:
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1. Arboreal origin:
Heilman, Osborn and Beebe hold that ancestors of the birds were arboreal. They used their extended forelimbs as parachutes while jumping from one tree branch to another, a view supported by De Beer (1954).
2. Cursorial origin:
Nopcsa believes that the ancestral Protoavis, was a biped cursor. It used to flap air with forelimbs to gain speed. Eventually they were able to take off from the ground and sustain them in air. Ostrom (1979) also holds similar view.
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3. Diving origin:
Newman considers the ancestor of birds, Protoavis, was an aquatic reptile. They soared over water to catch fishes, from which they might have acquired the ability to fly.
4. Compromise theory:
Gregory (1951) proposed a compromise theory. Carinates (flying birds) evolved from arboreal ancestor, while ratites originated from cursorial ancestor. For a long time confusion persisted about the probable habit of Archaeopteryx. De Beer (1954), Swinton (1960), Welty (1963) and others believe that Archaeopteryx was arboreal and a poor flier.
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A flat, keel-less sternum, primitive condition of pectoral girdle elements indicate its weak flying ability. The idea is supported by Yalden (1961). From the structure of pedal phalanges Ostrom (1974) suggests that the bird was a cursor.
He attaches a new function to clawed digits on its wings—to knock down the insect-prey to ground. Conical and recurved, socketed teeth helped them to pick up insects quickly from the ground. The climbing function of the clawed wing digits, advocated by early workers, however, was not supported by him.
Monophyletic/Di-phyletic Origin:
Lowe (1928, 1944), Bellaris and Attridge (1975) believe that birds are di-phyletic in origin. They hold that ratites differing from the carinates in several important features, represent a natural primitive group. They diverged from the ancestral stock quite early.
On the other hand majority of the workers believe that the birds are monophyletic. A fossil bird Eleutherornis is regarded as the probable ancestor of ostrich. Curiously enough, the fossil has remarkable affinity to the ancestor of flying bird (McFarland, 1979).