Feeding ecology and habitat of Late Pleistocene Equus horses from west-central Mexico using carbon and oxygen isotopes variation

Abstract

Using carbon and oxygen stable isotopes we analyzed the diet and habitat of three Late Pleistocene horses (Equus mexicanus, E. conversidens, and E. cedralensis) from two localities in west-central Mexico. Our objective was to evaluate dietary adaptability and resource partitioning, which would reflect the environmental conditions of the localities on which horses fed, and would support the ecological scenario predicted from morphology and ecomorphology. Our preliminary results show the presence of two feeding styles in La Cinta-Portalitos, indicating some resource partition and a more diverse environment: one of E. mexicanus with a diet composed by C3/C4 plants, and another one of E. conversidens and E. cedralensis with high consumption of C4 plants. Contrastingly, in La Piedad-Santa Ana only one feeding group was present, in which the three horse species fed mainly on C4 plants, thus possibly demonstrating the absence of resource partitioning and the abundance of a single food plant resource for horses. The major dietary variation we recorded was in E. mexicanus, followed by that in E. cedralensis and E. conversidens, which evidences that in the past, horses exhibited a more diverse diet related both to an eclectic behavior and to the varied environmental conditions in which they lived. We also found that the ecological predictions (habitat) based on ecomorphological characteristics were supported for some populations, but not for others; this indicates a complex relation between body mass, limb proportions and diet, more research being needed for better understanding of this relation. Finally, our results suggest a highly heterogeneous habitat with a mixture of C3 and C4 plants in La Cinta-Portalitos, and a more open scenario with a higher diversity of C4 plants and presence of woody vegetation of C3 plants in La Piedad-Santa Ana.