横断山区福东晚上新世种子/果实化石群的研究

The late Cenozoic experienced severe climatic and environmental changes, such as the decline of atmosphere CO2 concentration, global surface cooling, plateau uplift in East Asia and North America, and winter monsoon intensification. As a result, herbs began to diversify and flourish, becoming even dominant elements in many ecosystems. However, the availability of herb fossils is far from abundant. Thus, the past species diversity and distribtion pattern of numerous herb groups, as well as their phylogeny and biogeography, are unknown due to lack of fossil evidence. A set of seed and fruit fossils has recently been recovered from the late Pliocene Fudong flora in central Hengduan Mountians, northwestern Yunnan, China. The fossil materials are uncovered from Sanying Formation, which is late Pliocene in age based on stratigraphic correlation, floristic assemblage, mammalian fossils and palaeomagnetic evidence. The fossils are well-preserved and many of them bear detailed surface sculptures. They are three-dimensional, allowing for anatomical examination by X-ray tomographic microscopy. The major part of the fossil taxa are herbaceous, based on an initial taxonomical determination at the generic level. This might represent the first discovery of seed and fruit fossils of herbaceous plants in Hengduan Mountains, and one of the few such findings in China. In order to obtain a comprehensive picture of the seed and fruit fossil assemblage, much more fossil materials are to be systematically collected and taxonomically identified. The floristic composition and vegetation character will be analyzed. Palaeoclimates will be reconstructed by using the quantitative coexistence approach (CA). Detailed taxonomical studies of some fossil taxa, such as Dianthus, Rubus, Aralia, etc., as well as their past biogeography and even their potential in molecular clock calibration, are to be carried out. Fudong flora will be used as a representative for us to answer the herb species diversity in Hengduan Mountains during the geological past. The late Pliocene flourishing of herbs and existence of grasslands will be discussed for our better understanding of the associated mountain uplift, temperature decline and winter monsoon intensification in this region since the late Cenozoic. Additionally, the present seed and fruit assemblage are to be compared with leaf fossil assemblage, which have already been reported from the lower layers of Sanying Formation at Fudong, based on composition, the inferred vegetation type and the estimated palaeoclimates. Changes of plant diversity, vegetationa character and climatic condition there during the late Pliocene will also be discussed. This research project finished, four or five papers will be published, of which, around three or four are SCI papers.

晚新生代以来，随着全球大气CO2浓度和温度下降，冬季风加强，气候变干、变冷，草本植物逐渐兴起；然而，由于缺乏化石证据，草本植物诸多类群的种系分异、物种多样性和分布格局的形成知之甚少。本项目选取云南横断山晚上新世福东植物群三维立体保存、草本成分为优势的种子/果实化石群为研究对象，系统地采集化石材料，利用电镜扫描和X光层析投射扫描分别进行形态学和解剖学对比，准确鉴定化石，重建古区系和古植被，定量重建古气候，并通过总结悬钩子属、楤木属等类群的化石历史，探讨其系统演化和生物地理。同时，本项目以福东草本植物化石群为例，窥斑晚上新世横断山地区草本植物的基本面貌，揭示该地区草本植物的兴起和以草本植物为优势的植被类型的出现，从而探讨晚新生代以来横断山海拔抬升、气温下降、冬季风加强等地质气候事件，并通过对比种子/果实化石与下方层位的叶化石，探讨晚上新世福东地区植物和植被多样性，及多样性和古气候的演变。

横断山地处青藏高原东南缘，是我国乃至世界植物多样性最丰富的地区之一。为了解这种植物多样性的形成与演化，古植物学家依据植物化石证据对这一重要科学问题进行了探索和回答。然而，之前的植物化石主要以木本植物为主，草本植物稀少，因此，对横断山地质时期的草本植物多样性知之甚少。最近发现的地处横断山腹地的晚上新世三营组地层的福东植物群产大量三维保存的种子/果实化石，很多为草本成分，可能为揭示横断山地质时期的草本植物多样性提供重要证据。本项目系统采集了该植物群的种子/果实化石，借助显微镜、扫描电子显微镜和CT扫描，对化石进行了形态、解剖学研究，并通过与现生植物的对比，准确鉴定化石。共计新鉴定出14个类群，包括冷杉属、柏木属、刺柏属、苋属、蓼科、商陆属、悬钩子属、楤木属、栎属、花椒属、马鞭草属、菊科、苔草属、藨草属，加上之前报道的接骨木属和狗筋蔓属，共计16个类群，一定程度上反映了植物群的基本面貌。其中草本植物有7个类群，占近一半，一定程度上反应了草本植物的多样性。选择悬钩子属、楤木属和花椒属进行单独、详细的研究，描述了8个种，建立了3个化石新种，识别出悬钩子属的5个种，提出该属于晚上新世在横断山地区建立了较高的物种多样性，提出花椒属在我国西南地区持续性存在，推测第四纪冰期对西南地区的影响有限。利用共存分析，定量估算了种子/果实化石层及位于其地层学下方的叶片化石层的古气候，认为晚上新世的福东比现在温暖、湿润，推测该地自晚上新世以来，总体呈降温、变干的趋势，并发现降水季节性增强，推测可能与亚洲季风的加强有密切关系。