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-TAXONOMIC REVIEW OF THE PLEISTOCENE EQUIDS FROM MEXICO BASED ON DENTAL MORPHOLOGY.A quantitative and qualitative evaluation of the dental traits of five horse species from 15 fossiliferous areas from the Pleistocene of Mexico was performed. The purpose of this study was to evaluate whether Equus mexicanus, E. conversidens, E. excelsus, E. francisci (= E. tau) and E. cedralensis show particular dental morphologies (measurements and occlusal morphology of the molariform) that provide information of systematic significance. To this end, premolars and molars of adult individuals were used to evaluate a set of ten quantitative variables that were analyzed by bivariate and multivariate methods; also, 13 qualitative variables were used to estimate the frequency in the configuration and development degree of the enamel pattern on the occlusal surface for each species. Our results indicate that 60% of the quantitative variables and 40% of the qualitative provide information to distinguish dental morphologies. Based on measures and the enamel pattern the following specific characteristics were recognized: E. mexicanus: large-size occlusal area and relatively complex enamel pattern, E. conversidens: medium-size and moderately complex occlusal enamel and E. francisci: small-size and relatively simple enamel pattern on the occlusal surface. Concerning E. excelsus and E. cedralensis, their dental morphology is closely similar to those of E. conversidens and E. francisci respectively. The observed dental morphology of the Mexican specimens of E. excelsus indicates that part of those should be reconsidered as E. conversidens and part as E. mexicanus. Nevertheless, E. francisci and E. cedralensis are different species that can be recognized by limb characters rather than dental traits. Furthermore, the developing of particular dental patterns in these species is a factor that allowed their coexistence in Mexico during the Pleistocene.Key words: dental morphology, Equidae, Equus, taxonomy, Pleistocene, Mexico.RESUMO -No presente estudo foi realizada uma avaliação quantitativa e qualitativa das características dentárias de cinco espécies de cavalos de 15 áreas fossilíferas do Pleistoceno mexicano. Os objetivos do estudo foram de avaliar se Equus mexicanus, E. conversidens, E. excelsus, E. francisci (= E. tau) e E. cedralensis mostram morfologias dentárias particulares (medidas e morfologia oclusal de molariformes) que forneçam informações de importância sistemática. Para tal, pré-molares e molares de indivíduos adultos foram utilizados para avaliar um conjunto de dez variáveis quantitativas que foram analisadas por métodos bivariantes e multivariantes. Também foram utilizadas 13 variáveis qualitativas para estimar a frequência no grau de configuração e desenvolvimento do padrão de esmalte na superfície oclusal para cada espécie. Os resultados indicaram que 60% das variáveis quantitativas e 40% das qualitativas proveram informações para distinguir morfologias dentárias. De acordo com as medidas e o padrão do esmalte foram...

Pleistocene camels from Mexico include representatives of llamas and camels. Their record spans from the Early Blancan to the

Bison antiquus Leidy, 1852 was one of the largest and most widely distributed megafaunal species during the Late Pleistocene in North America, giving rise to the modern plains bison in the middle Holocene. Despite the importance of the ancient bison, little is known about its feeding ecology. We employed a combination of extended mesowear, and mesowear III to infer the dietary preference and habitat use of three Mexican samples of B. antiquus. These included two northern samples—La Piedad-Santa Ana and La Cinta-Portalitos—from the Transmexican Volcanic Belt morphotectonic Province, as well as one southern sample—Viko Vijin—from the Sierra Madre del Sur morphotectonic province. We found that the northern Mexican samples were primarily nonstrict grazers, whereas the southern sample displays a pattern consistent with mixed feeding habits. This suggests variability among the diets of the bison from these samples, caused by different paleoenvironments. This evidence complements the paleoenvironmental reconstructions in the studied localities; for the northern samples, open prairies composed of patches of woodland or shrubland and, for the southern locality, a fluvial floodplain with short-lived vegetation. In both scenarios, grasses (Poaceae) were nondominant. The dietary habits of our samples of ancient bison in Mexico are the southernmost dietary inference for the species in North America and expand our knowledge of the dietary habits of B. antiquus during the Late Pleistocene.