Isotopic record of palaeodiet of a 7.4 Ma Hipparionine fauna from the central Loess Plateau, northern China: Palaeo-ecological and palaeo-climatic implications

Abstract

Ecological shifts from C3 to C4 vegetation took place in many parts of the world around 7.5–5 Ma in response to global climate change. Previous evidences from pollen, paleosol isotope, and faunal have suggested that the expansion of C4 vegetation also occurred in the central Chinese Loess Plateau (CLP) at 7.4 Ma, which, however, is incompatible with palaeoclimate evidence from the CLP of cold and dry conditions during the late Miocene. In this study, stable oxygen (δ18O) and carbon (δ13C) isotope ratios preserved in tooth enamel from hipparionine were analyzed to elucidate the late Miocene (∼7.4 Ma) palaeoecology of the central CLP. The enamel δ13C values indicated a diet comprised entirely of C3 plants, consistent with the C3 steppe inferred from the faunal composition for the western district of the Neogene palaeozoogeographical boundary of Northern China. The δ18O values were indicative of a mild continental climate with Late Miocene seasonality that is not as pronounced as the modern steppe environment of Mongolia. The local landscape was most likely dominated by C3 steppe which belonged to the western district of the Neogene palaeozoogeographical boundary of Northern China. Comparison of results presented here and with published records from other localities in this region such as the Linxia Basin, Yushe and central Inner Mongolia suggests a veer of the East Asian summer monsoon (EASM) since 7.5 Ma.