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Coevolution of Grasses and Herbivores

G. Ledyard Stebbins
Annals of the Missouri Botanical Garden
Vol. 68, No. 1 (1981), pp. 75-86
DOI: 10.2307/2398811
Stable URL: http://www.jstor.org/stable/2398811
Page Count: 12
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Coevolution of Grasses and Herbivores
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Abstract

The appearance of fossilized silica bodies derived from the leaf epidermis of grasses and of mammalian fossils having high-crowned teeth was nearly simultaneous in lower to middle Eocene strata of Patagonia, where these fossils are associated with dry land sediments that indicate the presence of savannas containing shrubs and traversed by rivers that provided mesic habitats. In North America, the earliest clearly identified grass fossils are stipoid fruits of lower Miocene age, while the oldest mammals having high-crowned teeth are rhinoceroses of Miocene age. The abundant stipoid fruits known from the Miocene and Pliocene Epochs in the central United States indicate that the earliest Miocene species were quite different from modern counterparts, but that early Pliocene species have modern counterparts in the pampas of South America. During the Pleistocene, stipoid grasses ceased to be dominant elements of North American grasslands, being replaced by grasses belonging to the tribes Chlorideae and Andropogoneae. This change was associated with the appearance of a drier, more continental climate and with the appearance of bison and sheep on the North American plains. The evolutionary significance of these coordinated changes is discussed.

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