Stable carbon and oxygen isotopic evidence for Late Cenozoic environmental change in Northern China

Abstract Stable carbon and oxygen isotope ratios of 311 enamel samples from a diverse group of herbivorous mammals including Equidae, Rhinocerotidae, Bovidae, Rodentia and Ochotonidaewere were analyzed in order to reconstruct the Late Cenozoic history of vegetation and environmental change in the Yushe Basin in North China. The δ 13 C values of bulk and serial enamel samples from large mammals show a wide range of variation from − 13.3‰ to 1.4‰, with a mean of − 7.4‰ ± 3.5‰ (n = 294). This indicates that large herbivorous mammals in the area had a variety of diets since 6.5 Ma, ranging from pure C 3 to mixed C 3 –C 4 and pure C 4 diets. In contrast, the δ 13 C values of small mammals vary from − 11.9‰ to − 7.6‰, with a mean of − 9.7 ± 1.1‰ (n = 17), indicating that rodents and ochotonids were feeding mostly on C 3 plants. Variations in δ 13 C values within and between species reflect the variations in the habitat and the vegetation consumed by the animals. In general, horses had higher amounts of C 4 grasses in their diets than other contemporary taxa such as bovids, rhinos, rodents and deer, suggesting that horses exploited more open habitats such as grasslands while deer, rhinos and rodents may have preferred more C 3 vegetation, which is more indicative of forested environments. The carbon isotope data show that C 4 grasses have been an important component of horses' diets and of local ecosystems since ~ 6.5 Ma, confirming that the “late Miocene C 4 expansion” occurred in North China as it did in Africa, Indian subcontinent and the Americas. This supports a global factor as a main driver of the late Miocene C 4 expansion. The combined carbon and oxygen isotope data reveal major shifts in climate to drier and/or warmer conditions after ~ 5.8, ~ 4.1, ~ 3.3, and ~ 2.5 Ma, and significant shifts to relatively wetter and/or cooler conditions after ~ 6.4, ~ 5, ~ 3.5 Ma. The shifts to drier and/or warmer climate after ~ 5.8 Ma and ~ 2.5 Ma coincide with two major fauna turnover events. Intra-tooth δ 13 C and δ 18 O values are negatively correlated within individual modern teeth and some fossil teeth, displaying the characteristic pattern of the summer monsoon regime and confirming a strong monsoon influence in the area since at least the early Pliocene. The data also suggest that the C 4 abundance in the area has fluctuated over the past 6.5 Ma in response to changes in climate, with more C 4 grasses during warmer and/or drier periods and a reduced C 4 component at cooler and/or wetter times.