Neogene records of environmental change in the Great Plains, U.S.A., derived from paleosols and paleodietary studies of fossil horse teeth exhibit surprising contrasts. Stable carbon isotope (d13C) values in horse tooth enamel indicate C3-dominated diets throughout the Miocene until about 6.6 Ma, at which point several species began to consume C4 vegetation. The d13C composition of paleosol carbonates suggests C4 grass comprised about 20% of plant biomass throughout the Miocene, increased to about 40% of biomass by the early Pliocene, and reached modern abundance by the early Pleistocene. A possible explanation for the low variability in Miocene paleosol D13C values is that habitats dominated by C4 grasses were patchily distributed across the landscape and migrated laterally on timescales rapid relative to carbonate formation. I examined d13C isotopes in tooth enamel of seven different camelidae genera from the middle-late Miocene of Nebraska to determine whether there is a correlation between the isotope values recorded in horse and camel teeth and what those results could mean in relation to the paleosol data.