Paleoenvironment of the late Miocene Shuitangba hominoids from Yunnan, Southwest China: Insights from stable isotopes

摘要

The Late Miocene witnessed significant changes in climate globally and was an important time in the evolution of hominoids. Here, we report the results of an isotopic study of Late Miocene mammalian teeth and freshwater shells from Shuitangba (Yunnan Province, China)-an important refugium for hominoids, and reconstruct paleoenvironmental conditions in the area. δ~(13)C values of fossil enamel samples range from - 15.5‰ to -1.0‰, with a mean of -11.3 ±2.3‰, and δ~(18)O values vary from -14.2 to -4.6‰, averaging -9.7 ±2.2‰. Reconstructed diet-δ~(13)C values for these fossil mammals indicate that although they fed mostly on C3 plants, many of them consumed some C4 vegetation. This suggests that the local ecosystem contained C4 grasses but was dominated by C3 plants. The intra-tooth δ~(18)O variation of fossil herbivores is larger than what is found in modern herbivores. Reconstructed paleo-meteoric water δ~(18)Ow values are on average lower than those inferred from modern samples and also lower than the average δ~(18)Ow values of modern precipitation in the region. Similarly, δ~(18)O values of fossil freshwater shells display a larger seasonal variation and are significantly lower than modern shells from Fuxian Lake in the same region. Thus, the δ~(18)O data from both mammalian teeth and freshwater mollusk shells support a wetter climate, possibly with a stronger precipitation seasonality in the Late Miocene than today. Comparison of clumped isotope temperatures from fossil and modern shells suggests a mean annual temperature of ~15 to 16 °C in the Shuitangba area in the Late Miocene, which is ~3 to 4 °C higher than that of today. Taken together, our isotope results suggest that C4 grasses existed in local ecosystems in the area, likely in patches of grasslands or wooded grasslands in a mostly forested environment in the Late Miocene when the local and regional climate was warmer and wetter than today. Comparison of the δ~(13)C records from Yunnan and t