Dietary adaptability of Late Pleistocene Equus from West Central Mexico

Most of the Pleistocene species of Equus from Mexico have been considered to be grazers and highly specialized on the basis of their craniodental features, and therefore analogous to their modern relatives from an ecological point of view. Here we rely on dental wear analyses of three different species of Rancholabrean Equus that exhibit differences in limb proportions and body mass and occurred in two different habitats in order to test whether species exhibited more heterogeneous dietary capabilities compared to modern horses. Overall, and although our analyses show grazer lifestyles, there is a significant degree of dietary variability among taxa according to the site, apparently as a response to differences in climate and environmental conditions, with intermediate feeding preferences on the basis of the last items consumed during the last days prior to death in some cases. Accordingly, fossil Equus might have been more sensitive to different environments and diverse in terms of dietary preferences, thus incorporating a higher proportion of browse vegetation if necessary, than their modern relatives. These results highlight the dietary plasticity of certain fossil species, and evidence the caution that should be paid when reconstructing the ecology of fossil species using their modern relatives as analogs.