ABSTRACT

Various lines of evidence indicate that global terrestrial environments underwent major transformations in the late Miocene. Prior to the late Miocene, terrestrial ecosystems consisted primarily of C3 plants. C4 grasses, which are common in low-elevation tropical to temperate ecosystems today, either did not exist or were a minor component of the local biomass until the late Miocene. Several hypotheses have been proposed to explain the cause of the late Miocene C4 expansion, but there is a large gap in data coverage in East Asia.

This project plans to establish detailed isotopic records of late Cenozoic vegetation and climate changes and to document changes in mammalian fauna at two fossil localities - the Tunggur and Tianshui basins - in northern China. These basins contain long sequences of Neogene sedimentary records and rich vertebrate fossils. Our primary objectives are: (1) To examine changes in the diet of fossil mammals at these localities against patterns of turnover, extinction and changes in species richness and composition; (2) To determine the temporal pattern in the spread of C4 grasses in these basins; (3) To determine whether the carbon and oxygen isotopic shifts seen at these localities reflect local or regional to global climatic changes through comparison with well-established records elsewhere (for example, the Siwalik record of South Asia); (4) To determine whether changes in climatic conditions seen in the oxygen isotopic records correspond to any of the proposed uplift events and/or biotic changes documented by carbon isotopes and fossils; and (5) To place the isotopic trends seen in local mammalian assemblages in the context of ecomorphological change across taxa.

This research will not only fill a critical gap in the global coverage of C4 expansion, but also help to elucidate the impact of late Cenozoic Himalayan-Tibetan uplift on C4 plant expansion, climate and mammalian evolution in northern China and test hypotheses concerning the late Miocene "global expansion" of C4 plants and the style of uplift of the Himalayan-Tibetan Plateau.

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