Collaborative Research: The Impact of Late Cenozoic Himalayan-Tibetan Uplift on C4 Plant Expansion, Climate and Mammalian Evolution in Northern China

各种各样的证据表明，全球陆地环境在中新世晚期经历了重大转变。中新世晚期之前，陆地生态系统主要由C3植物组成。C4草在今天的低海拔热带到温带生态系统中很常见，直到中新世晚期才存在，或者只是当地生物量的一小部分。对于晚中新世C4扩张的原因，人们提出了几种假说，但在东亚地区的数据覆盖范围存在较大差距。该项目计划建立中国北方晚新生代植被和气候变化的详细同位素记录，并记录两个化石地点（钨谷盆地和天水盆地）哺乳动物区系的变化。这些盆地具有较长的新近系沉积记录序列和丰富的脊椎动物化石。我们的主要目标是：(1)研究这些地区化石哺乳动物的饮食变化与物种丰富度和组成的变化模式的更替、灭绝；(2)确定C4禾本科植物分布的时间格局；(3)通过与其他地区（如南亚的Siwalik记录）的比较，确定这些地区的碳和氧同位素变化是否反映了当地或区域到全球的气候变化；(4)确定氧同位素记录中气候条件的变化是否与碳同位素和化石记录的任何隆起事件和/或生物变化相对应；(5)将本地哺乳动物群落的同位素变化趋势置于各类群生态形态变化的背景下。该研究不仅填补了全球C4扩张覆盖的关键空白，而且有助于阐明晚新生代喜马拉雅—青藏高原隆升对中国北方C4植物扩张、气候和哺乳动物进化的影响，并验证关于晚中新世C4植物“全球扩张”和喜马拉雅—青藏高原隆升方式的假设。

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.