华南早三叠世腕足动物的残存—复苏过程研究

Brachiopods were one of the most dominant benthic faunas in the Paleozoic oceans, but are also one of the largest group of victims among the leading fossil groups that suffered the end-Permian mass extinction, after which their ecological dominance was taken over by the mollusks. To this point, the recovery of the Triassic brachiopods which were vulnerable groups could better indicate the full recovery of benthic communities. Previous studies suggested that, the benthic communities did not show recovery until the Middle Triassic. However in our recent findings, a number of early Triassic brachiopods which belong to the Mesozoic type were uncovered from the lower Triassic strata in several areas of South China. This is a key clue connecting the extinction and recovery. On this basis, this study will search more distribution layers that contain early Triassic brachiopods, make clear their stratigraphical characteristics and regional distribution, explore the survival and recovery process following the end-Permian mass extinction, and provide reference for the restoration of ecosystem in the early Mesozoic. In addition, the research findings on physiology and research methods on ecology of modern organisms will be applied to investigate the survival and adaptive mechanisms of brachiopods in the stressful environment. This may indicate the role of survival brachiopods in the recovery and radiation process, and provide inspiration of how modern organisms escape from present ecologic crisis.

腕足动物是古生代海洋中最具代表性的底栖类群，同时也是古、中生代之交生物大灭绝事件中最大的受害者之一，此后其生态优势性被软体动物所取代。从这点来看，腕足类在三叠纪已经成为弱势群体，它的复苏更能代表整个底栖群落的全面复苏。前人研究认为二叠纪-三叠纪之交大灭绝之后底栖生物的复苏开始于中三叠世，而申请人及团队最近在华南多个地区的下三叠统地层中发现有中生代类型的腕足动物化石，这是连接灭绝和复苏不可多得的纽带。在此基础上，本项目将发掘更多的下三叠统腕足化石分布层位，弄清它们的产出地层特征和区域分布规律，探讨腕足动物在二叠纪-三叠纪之交生物集群灭绝后的残存—复苏过程和型式，为中生代初生态系重建过程提供参考；同时利用现代生物的生理学研究成果和现代生态学理论及方法，研究腕足动物对灾变环境的残存和适应机制，揭示残存型腕足分子在生物复苏—辐射中所起的作用或指示的意义，从而为现代生物如何躲过生态危机提供启迪。

本项目通过对湖北利川尖子山剖面系统采集的306枚完整的腕足动物化石进行处理和鉴定，得到3属3种，其中包括1个新属和1个新种。通过与全球同时期腕足动物面貌对比发现，该腕足动物群填补全球范围内迪纳尔亚期残缺不全的腕足动物数据库，并且这一腕足动物群也已成为目前全球范围内迪纳尔亚期最具代表性的腕足动物群。对腕足类化石的古地理研究发现，Norellidae科的腕足类在早三叠世印度期仅分布于我国华南地区，即起源于华南，到奥伦尼克期迅速迁移至高纬度地区。对华南晚二叠世至中三叠世3416枚腕足动物标本的大小研究显示，腕足个体从晚二叠世到三叠世最早期急剧减小，到奥伦尼克期才明显增大。分析得到，腕足个体大小的变化与环境压力和生存竞争都有关系，二叠纪-三叠纪之交个体大小的急剧减小可能与二叠纪-三叠纪之交的环境因素有关，早三叠世个体逐步增长是由于生物自身的一些因素，如生理因素、竞争因素或捕食因素。此外，本项目研究的腕足动物群很好地证明了早三叠世的腕足动物呈现出一个快速复苏的过程。通过对古环境分析，发现生物的快速复苏与海水缺氧状况的好转有关。不同地区，生物复苏的时间不同，主要取决于环境条件是否好转。基于此发现，提出三叠纪生物复苏的新模式：“不均匀复苏”模式。