A survey of horse-teeth wear during the past 55 million years implies that evolutionary pressures were generally low.

During the late Pleistocene and early Holocene, Bisonwas widely dispersed across North America and occupied most regions not covered by ice sheets. A dietary study onBisonpaleopopulations from Alaska, New Mexico, Florida, and Texas was performed using two methods that relate dental wear patterns to diet, mesowear analysis and microwear analysis. These data were compared to a mixed sample of extantBisonfrom the North American central plains, extant woodBisonfrom Alberta (Canada) and a variety of other modern ungulates. Mesowear relates macroscopic molar facet shape to levels of dietary abrasion. The mesowear signature observed on fossilBisondiffers significantly from the hyper-abrasive grazing diet of extantBison. Tooth microwear examines wear on the surface of enamel at a microscopic scale. The microwear signal of fossil samples resembles to modernBison, but the fossil samples show a greater diversity of features, suggesting that fossilBisonpopulations regularly consumed food items that are texturally inconsistent with the short-grass diet typical of modern plainsBison. Mesowear and microwear signals of fossilBisonsamples most closely resemble a variety of typical mixed feeding ungulates, all with diets that are substantially less abrasive than what is typical for modern plainsBison. Furthermore, statistical tests suggest significant differences between the microwear signatures of the fossil samples, thus revealing geographic variability in PleistoceneBisondiets. This study reveals that fossils are of value in developing an understanding of the dietary breadth and ecological versatility of species that, in recent times, are rare, endangered, and occupy only a small remnant of their former ranges.

(2007). Effect of ontogenetic-age distribution in fossil and modern samples on the interpretation of ungulate paleodiets using the mesowear method. Journal of Vertebrate Paleontology: Vol. 27, No. 3, pp. 763-767.