. Animal biology. Zoology; Biology. 410 METAZOAN PHYLA hummingbird found in Central America is only 1}^^ inches long from the base of the bill to the base of the tail. 428. Origin of Birds and of Flight.—A former theory of the origin of birds was that they were derived from the flying reptiles, or ptero- dactyls. These reptiles, however, do not resemble birds structurally in the degree that some of the bipedal dinosaurs (Fig. 299) do. At the present time, therefore, the latter are usually looked upon as the ancestors of Fig. 298.—One conception of the appearance of Archaeopteryx macrur
. Animal biology. Zoology; Biology. 410 METAZOAN PHYLA hummingbird found in Central America is only 1}^^ inches long from the base of the bill to the base of the tail. 428. Origin of Birds and of Flight.—A former theory of the origin of birds was that they were derived from the flying reptiles, or ptero- dactyls. These reptiles, however, do not resemble birds structurally in the degree that some of the bipedal dinosaurs (Fig. 299) do. At the present time, therefore, the latter are usually looked upon as the ancestors of Fig. 298.—One conception of the appearance of Archaeopteryx macrura Owen, based upon a specimen in the British Museum. {From Wieman, "General Zoology," after Romanes, by the courtesy of McGraw-Hill Book Company, Inc.) X J^. Different theories of the origin of flight have been proposed but the most probable theory seems to be the one which traces the develop- ment of wings to the broadening of the limbs and tail due to the increase in length of scales and their modification to form feathers. Apparently early birds had flight feathers both on their fore- and on their hind limbs and on both sides of the tail. Such a bird was capable of gliding through the air from a tree or elevated point, perhaps to a considerable distance. Gradually the forelimbs developed into wings, the feathers disappeared from the hind limbs, and the tail shortened and became modified into such a tail as birds possess today. 429. Flight.—In sustained flying the wings strike downward and forward and the bird rides over the air, which serves to buoy it Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Wolcott, Robert Henry, 1868-1934; University of Nebraska (Lincoln campus). Dept. of Zoology. New York ; London : McGraw-Hill Book Company, Inc.
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