Identifier: americanaunivers08newy (find matches)
Title: The Americana; a universal reference library, comprising the arts and sciences, literature, history, biography, geography, commerce, etc., of the world
Year: 1908 (1900s)
Authors:
Subjects: Encyclopedias and dictionaries
Publisher: New York : Scientific American Compiling Dept.
Contributing Library: University of California Libraries
Digitizing Sponsor: Internet Archive

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od becomes difficult to obtain,the animal being compelled to devote nearly allits time to getting enough to eat. Cause of the Evolution.— The evolution ofthe horse, adapting it to live on the drj- plains,probably went hand in hand with the evolutionof the plains themselves. At the commencementof the Age of Mammals the western part of theNorth .\merican continent was by no means ashigh above sea-level as now. Great parts of it hadbut recently emerged, and the Gulf of Mexicostill stretched far up the valley of the Mis-sissippi. The climate at that time was probablyvery moist, warm and tropical, as is shown bythe tropical forest trees, found fossil even asfar as Greenland. Such a climate, with the lowelevation of the land, would favor the growthof dense forests all over the countrj. and tosuch conditions of lite the animals of the be-ginning of the Mammalian period must have beenadapted. During the Tertiary the continent wassteadily rising above the ocean-level, and at the Hvpoiiiirrs.
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Courtesy of the Philadelphia Cuinmcrcial Museum. SKELETON FRO.M .MIDDLE MIOCENE BEDS. NEAR PAWNEE.BUTTE. COLORADO. HORSE same time other influences were at work tomake the climate continually colder and drier.The coming on of a cold, dry climate restrictedand thinned the forests and caused the appear-ance and extension of open, grassy plains. Theancient forest inhabitants were forced either toretreat and disappear with the forests, or toadapt themselves to the new conditions of life.The ancestors of the horse, following the lattercourse, changed with the changing conditions,and the race became finally as we see it to-day,one of the most highly specialized of animals inits adaptation to its peculiar environment. Atthe end of the Age of Mammals the continentsstood at a higher elevation than at present, andthere was a broad land connection between Asiaand North .America, as well as those now exist-ing. At this time the horse became cosmopoli-tan, and inhabited the plains of all the great

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