藏北伦坡拉、尼玛盆地古近纪化石鱼类的系统学和生物地理学研究

The uplift of the Tibetan Plateau has reorganized Asia’s geographical and drainage features, which must have profound impact on the diversification and dispersal history of Asian freshwater fishes. But how? Lying in the center of this scientific issue is the reconstruction of the evolutionary history of Tibetan paleoichthyofaunal during the Cenozoic. However, this subject is hampered by the scarcity of fossil records throughout the plateau, as well as the controversies on the uplift process of the plateau. Fortunately, numerous fossil fishes were discovered recently from the Paleogene fluvial and lacustrine strata of Lunpola and Nima basins in the interior of the Tibetan Plateau. These fossils include not only some closely-related species of the snow carps endemic to the plateau today, but also primitive fossil members of lineages with a disjunct African-Asian distribution, and other unknown species. The taxonomic diversity of these materials and the unexplored target layers in the basins promise more fossil findings and greater research opportunities ahead. Inspired by the achievement of previous research, this project focuses on the systematic and paleobiogeographic investigations of these fossils from there. It aims to reconstruct the taxonomic composition of these fishes and their distribution pattern and evolutionary sequence via anatomical observations of fossils and stratigraphical work on relevant strata, and discuss their paleoenvironmental implications. It also includes the phylogenetic analyses to resolve the interrelationships between the fossil taxa and their living relatives based on the combination of morphological and molecular data. These total evidence-based phylogenetic frameworks calibrated with fossils will estimate the divergence time and origin areas of some groups. The results of this project will highlight the role the evolution of Tibetan paleoichthyofauna played in the formation of current distribution of the freshwater fishes in Asia and related continent.

淡水鱼类在高原隆升背景下的演化过程是青藏高原生命史的重要组成部分。然而，由于化石材料的稀缺以及对隆升历史的不同认识，新生代高原鱼类的面貌及其演替过程不甚明了。最近藏北伦坡拉、尼玛盆地古近纪河湖沉积物中出现大量保存精美的鱼化石，所属类群包括今天高原所特有鱼类（如裂腹鱼类）的近亲，还有今天间断分布于非洲和亚洲热带地区鱼类的化石代表以及其他未知种类；其分类多样性和盆地内未深入考察的化石层预示了广阔的研究前景。在先前工作的基础上，本项目拟对以上盆地的古近纪化石鱼类进行细致的形态解剖学和系统学研究，结合更深入的地质地层学工作，确定古近纪本地区鱼群的组成面貌和时空分布特点，讨论其古环境意义；运用全证据的方法，结合形态学和分子学数据进行系统发育关系分析，用化石类型校正分子钟，重建特定类群的生物地理学历史，藉此探讨新生代高原地区鱼类区系的演变在亚洲乃至更广大地区现代鱼类区系形成过程中所起之作用。

本项目旨在重建藏北地区（青藏高原中部）始新世中期至中新世早期鱼类多样性组成及其演变，并以西藏的化石为基础，重建攀鲈等呈间断分布的鱼类之动物地理学历史。我们认识到藏北古近纪鱼类为喜暖水的生活于低地水域的鱼类（如攀鲈（鲈形目）、鲃（鲤科）和未知鲶科鱼类），至新近纪早期演变为以原始裂腹鱼为代表的适应中等海拔水域的鱼类。以西藏始攀鲈（Eoanabas thibetana）—迄今已知最古老、最原始的攀鲈科代表—约束攀鲈家族时间树，推测了亚洲-非洲攀鲈类分化时间约在距今4000万年前，动物地理学分析结果显示，攀鲈类起源于始新世的东南亚热带地区，扩散至西藏地区后经印度次大陆扩散至非洲大陆，并在那演化出高于亚洲同类的多样性。我们将这个过程表述为“印度跳板”说，以此挑战了解释攀鲈动物地理学历史的传统假说，即“冈瓦那起源”说和“新近纪亚非陆桥扩散”说。本项目再现了鱼类演化对青藏高原中部古近纪-新近纪古环境变化的响应，从生物地理学的角度看，也提供了包括鱼类在内的多方独立证据，显示青藏高原可能是现代陆地生物多样性形成的一个演化枢纽。