Using carbon and oxygen isotopic relationships from dental enamel, diet and habitat were inferred for both mesomammals and megamammals that lived in Cedral (San Luis Potosi, north-central México) during Late Pleistocene time. δ13C and δ18O values show that bison, some horses and mammoth were eating C4 plants and lived in open areas, while tapir, camel and some llamas ate C3 plants and inhabited closed areas. All other studied herbivores (pronghorn, glyptodont, mylodont ground sloth, javelina, mastodon, and other llamas, horses and mammoth) had a C3/C4 mixed diet, living in areas with some percentage of tree coverage. On the other hand, American lion and dire wolf ate either C4 or mixed-diet herbivores, and short-faced bear ate C3 herbivores. At Cedral, more humid conditions existed than presently, allowing the presence of a forested area near the grassland.