Feeding and environmental studies on late Pleistocene horses in mid-latitudes of South America (northern Uruguay)

The first analyses of carbon and oxygen stable isotopes (δ¹³C, δ¹⁸O) on horses of late Pleistocene beds, between 50 and 30 kyr B.P., at mid-latitudes of South America (northern Uruguay), are reported here. Isotopic analyses on Equus neogeus and Hippidion principale were made on tooth enamel, considering the Suess Effect. Isotopic values have been used as indicators of diets and environmental conditions, alongside with Hypsodonty Index, to pinpoint specific feeding strategies as grazer or browser. E. neogeus was a mixed-grazer that fed mostly on C₃ grass in open wooded areas and grasslands with a variable proportion of C₄ grass in the diet. H. principale was a mixed feeder with preference for open canopy wooded floor C₃ grass and plants. These results could explain the co-occurrence of both taxa that evolved a combination of feeding and habitat preferences that resulted in niche differentiation. The isotopic data supports the diversity of habitats previously proposed by other authors and corroborate the environmental context associated to the mammal assemblage in late Pleistocene at these latitudes of South America. Juveniles show δ¹³C depletion and δ¹⁸O enrichment related to adults. This shift could be explained by maternal effect, owing to gestation and lactation (depleted δ¹³C and enriched δ¹⁸O). The later because breast milk is significantly enriched in δ¹⁸O in comparison to drinking water and also is not fractionated in the same way as plant-derived carbon.