滇东南马关中新世果实化石的研究

Southeast Yunnan is situated in the southern subtropical zone, which floristically spans the Paleotropical Kingdom and Eastern Asiatic Kingdom. The flora of Southeast Yunnan is characterized by rich floristic elements of different origins and wealth of primitive and endemic genera, and for this reason, it earned its name of paleoendemism center. There have been long major interests to understand the evolutionary history and formation of Southeastern Yunnan flora. Cenozoic plant fossils are important materials address this scientific question. Recently, abundant fossil fruits have been newly recovered from the early Miocene of Maguan basin, Southeast Yunnan. Preliminary study showed that many fossils represent the first fossil record of the corresponding genera and many fossils represent those of extinct genera. Thus these fruit fossils are important materials for understanding the floristic evolution of Southeast Yunnan. In this project, the macromorphological and micromorphological characters of the fossils will obtained by multiple methods including CT scanning and electron scanning techniques. Then the fossil will be morphologically compared with those of the extant and fossil species to achieve their accurate identifications. Finally, the list of identified fossils, combined with previous floristic studies of Southeast Yunnan and literatures of environmental change in Southeast Yunnan, the change of Southeast Yunnan flora and its relationship to environmental change will be explored. Besides, characteristics elements including Zenia and Deviacer will be chosen to reconstruct their phytogeographic history by summarizing their fossil records and incorporating literatures including geological background, which will facilitate the understanding of the origin and evolution of characteristics elements in Southeast Yunnan flora. This project will provide important information for the evolution and formation of Southeast Yunnan flora and its relationship to environmental change.

滇东南地处南亚热带，横跨古热带和东亚植物区，各种植物区系成分交汇，古老、特有属丰富，素有古特有属分布中心之称。该地区植物区系的演化和形成历来备受关注，而新生代植物化石是开展此项研究的关键材料。申请人在滇东南马关下中新统发现了一批从未报道过的果实化石，其中首次发现的化石记录和灭绝属的化石丰富，是认识滇东南植物区系演化的珍贵材料。本项目拟通过CT扫描、扫描电子显微镜等现代技术解析化石的宏观、微观形态学特征，并与现生、化石种广泛对比，准确鉴定化石，认识滇东南早中新世植物区系的组成，并结合已有植物区系和环境变化资料，探讨滇东南植物区系的改变及其与环境背景的相关性；此外，将选取特征类群任豆属、远志槭属等，通过总结化石历史，结合分子生物学、地质背景等资料，开展古植物地理学研究，以此为例窥豹滇东南植物区系特征成分的来源和发展。本项目将为揭示滇东南植物区系的演化历程及其与环境背景的相关性提供基础资料。

滇东南地处世界生物多样性热点地区，是我国的“古特有属分布中心”，我国1/4的种子植物物种分布于此。滇东南植物区系的演化历来备受关注，而古植物学研究能够为回答这一问题提供直接证据。项目以滇东南马关植物群果实化石为研究材料，从3个方面开展研究：1）果实化石的分类鉴定；2）特征类群的古植物地理学；3）果实化石的植物区系演化意义。取得了以下研究成果：1）基于滇东南文山盆地的火山凝灰岩测年结果、哺乳动物化石及植物化石组合，将马关植物群的时代重新厘定为晚始新世。2）通过多种技术手段获取了果实化石的宏观、微观形态学信息，并与现生种及化石种进行了形态学比较，鉴定了果实化石类群21种，隶属于18属。其中，裸子植物2属，包括红杉属和翠柏属；被子植物16属，包括椿榆属、肋果茶属、远志槭属、槭属、榆属、鹅耳枥属、滇桐属、蚬木属、梣属、见血飞属、老虎刺属、任豆属、单籽豆属、香槐属、羊蹄甲属和马甲子属。任豆属、肋果茶属和老虎刺属是这3属化石的首次发现，椿榆属和见血飞属化石是亚洲新纪录。3）在此基础上开展了特征类群的古植物地理学研究：提出了香槐属至少在晚始新世就存在于亚洲并在始新世暖期通过白令陆桥实现在北美和亚洲之间区系交流的假说；报道了羊蹄甲属最早的化石记录，认为该属在我国西南一个狭小地区就有极高的多样性这一现象至少可以追溯到晚始新世；提出了滇桐属起源于东北亚后通过中亚及西藏中部迁移到了我国西南的观点。4）基于本项目的研究，同时结合已有研究资料，发现了滇东南植物区系总体较为稳定，但又存在植物灭绝现象这一特征：本项目鉴定出的18属植物中有14属目前还见于化石点周边地区，体现了区系的保守性和继承性；而植物群中的灭绝类群，表明滇东南植物区系在其演化历程中发生过明显的类群灭绝事件。滇东南植物区系的稳定性可能与滇东南总体稳定的地质背景有关，而局部灭绝事件可能与东亚季风气候增强从而使得不耐受冬季干旱的类群灭绝有关。