File:Geology (1907) (14776117502).jpg

Identifier: geology00cham (find matches)
Title: Geology
Year: 1907 (1900s)
Authors: Chamberlin, Thomas C. (Thomas Chrowder), 1843-1928 Salisbury, Rollin D., 1859- joint author
Subjects: Geology
Publisher: New York, H. Holt and co.
Contributing Library: Internet Archive
Digitizing Sponsor: Internet Archive

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5.—An American Miocene Camel, Oxydactylus longipes Peterson, from theLoup Fork beds of Nebraska. (After Peterson.) evolving horse to the open dry plains and their grassy food (Fig. 456).The elimination of the side toes, the lengthening of the limbs, thechange of the joints to the pulley-wheel type, the concentrationof the limb muscles near the body to reduce the weight of the partsmost moved, and the consolidation of the leg bones, were modifica-tions in the interest of combined speed and strength. A correspondingelongation of head and neck was necessary to reach the ground. Thefront teeth were reduced to chisel-like, cropping forms, somewhatresembling those of the rodents, while the molars evolved a tortuousdistribution of the enamel so flanked by dentine and cement thatthe differences of wear gave rise to ridges of enamel suited to grinding,and protected against breaking by supporting dentine and cementon either side. The teeth were also gradually elongated to provide 288 GEOLOGY.
Text Appearing After Image:
THE MIOCENE PERIOD. 289 for the great wear caused by the dry silicious grasses.1 It is probablyas safe to infer a development of dry grassy plains from this evolu-tion of the horse, as to infer climatic and topographic conditions fromplants and other organic adaptations, and hence it is probably safeto interpret the western basins as lodgment plains of the subaerialrather than of the strictly lacustrine type, so far as the nature of thedeposits leaves the question open. The tapirs and rhinoceroses.—The tapirs were but slightly repre-sented, but the rhinoceroses, though the running and swimming brancheshad dropped away, were a prominent feature in the fauna. The Ameri-can species were still mainly hornless (Aceraiherium), slight indica-tions of horns appearing in a single genus (Diceratheriutn). Two-horned species, however, appeared during the period in Europe. The carnivores.—The carnivores were abundant, and had assumedforms referred with some doubt to the living genera Cants, Fe

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