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Paleodietary trends for North American horses from Hyracotherium (early Eocene) through Equus (late Pleistocene) were examined using dental microwear analysis. Over 1200 fossil specimens were analyzed for enamel microwear and results were compared to an extensive microwear database of extant ungulates. This study tests the hypothesis that Eocene horses browsed on low abrasion foods whereas Oligocene and later horses had more abrasive diets concomitant with the spread of more open habitats and examines the correlation between the acquisition of hypsodonty and the beginning of grazing. Microwear results indicate that early to middle Eocene species engaged mostly in fruit browsing. In contrast, late Eocene to Oligocene taxa have microwear scratch numbers typical of grazing and mixed-feeding ungulates, but with very fine scratch textures which are unusual in modern C₄ grazers and indicate …