Project Gutenberg #20417
The Outline of Science, Volume 1
J. Arthur Thomson
1922Thomson's broad popular-science survey of astronomy, biology, and Earth science, prepared section by section from Project Gutenberg HTML.
Project Gutenberg #20417 Public domain in the United States Cover source Local typographic cover created for MojiMori from public-domain source metadata
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The Jurassic period showed a continuance of the reptilian splendour. They radiated in many directions, becoming adapted to many haunts. Thus there were many Fish Lizards paddling in the seas, many types of terrestrial dragons stalking about on land, many swiftly gliding alligator-like forms, and the Flying Dragons which began in the Triassic attained to remarkable success and variety. Their wing was formed by the extension of a great fold of skin on the enormously elongated outermost[Pg 100] finger, and they varied from the size of a sparrow to a spread of over five feet. A soldering of the dorsal vertebr as in our Flying Birds was an adaptation to striking the air with some force, but as there is not more than a slight keel, if any, on the breast-bone, it is unlikely that they could fly far. For we know from our modern birds that the power of flight may be to some extent gauged from the degree of development of the keel, which is simply a great ridge for the better insertion of the muscles of flight. It is absent, of course, in the Running Birds, like the ostrich, and it has degenerated in an interesting way in the burrowing parrot (Stringops) and a few other birds that have "gone back."