Coevolution of Grasses and Herbivores

Abstract

The appearance of fossilized silica bodies derived from the leaf epidermis E grasses visis mammalian fossils having high-crowned teeth was nearly simultaneous in m middle Eoc strata of Patagonia, where these fossils are associated with dry land sedimen vat indicate the America, the earliest clearly identified grass fossils are stipaid dir of lower Miocene ES 'while the oldest mammals having high-crowned teeth are derape es of Miocene age.The abundant stipoid fruits known from the Miocene and Pliocene Epochs in the d United States indicate that the earliest Miocene species were quite different from ES 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