Diet and habitat of unique individuals of Dinohippus mexicanus and Neohipparion eurystyle (Equidae) from the late Hemphillian (Hh3) of Guanajuato and Jalisco, central Mexico: stable isotope studies

Abstract

Stable carbon and oxygen isotopes were determined in molar enamel from fossil Pliocene equids from Rancho El Ocote in the San Miguel Allende basin, Guanajuato, and from Santa María, Tecolotlán basin, Jalisco. At each locality, the source was one molar from an individual Dinohippus mexicanus and one molar from an individual Neohipparion eurystyle. Results indicated that the N. eurystyle individuals from both localities had been C₃/C₄ mixed feeders, and had lived in open-zone vegetation (δ¹³C: -3.1‰ to -1.3‰; δ¹⁸O: -4.9‰ to -6.4‰). On the other hand, the D. mexicanus from Rancho El Ocote had fed upon C₄ plants and lived in open zones (δ¹³C: -1.3‰; δ¹⁸O: -4.9‰), whereas the D. mexicanus from Santa María was a C₃/C₄ mixed feeder with considerable consumption of C₃ plants (δ¹³C: -7.7‰; δ¹⁸O: -6.4‰). These results could be contrast to suggestions from previous isotopic work that D. mexicanus in Mexico predominantly fed on C₄ plants and further samples analyses are warranted. This study contributes to the understanding of the Pliocene equid taxa from central Mexico and emphasizes the presence of different diets, ranging from exclusive C₄ to mixed C₃/C₄ plants.