安徽南部奥陶—志留纪过渡期特异埋藏海绵动物群

The end-Ordovician mass extinction is the earliest and the second largest among the Big-five in Phanerozoic, which has been attracting increasing attention since the 1970s. Many fossils have been found from the rocks chronostratigraphically corresponding to the interval from the first episode of the end-Ordovician mass extinction to the latest Ordovician, such as brachiopods, trilobites, corals, graptolites and so on. Different groups show varied changes in strategy during this crisis event. As a group of sessile filter-feeding metazoans, sponges could be facilitators of the revival of ecosystems following the Late Ordovician ecological crisis. However, sponges are rare in the Ordovician-Silurian boundary interval, it seems that there is an “evolutionary gap” of sponges from the first episode of the mass extinction to the beginning of Silurian. Due to the sparse fossil record, the biodiversity pattern of sponges during and after the crisis (e.g. late Hirnantian and early-mid Rhuddainan) is still unclear. The present study will systematically analyze the phylogeny of sponges during the end-Ordovician mass extinction in South China on the basis of the detailed study of sponge systematics and cladistics. Moreover, through multidisciplinary cooperation, including paleontology, sedimentology, taphonomy and palaeoecology, we are determined to investigate the marine ecosystem before and after the end-Ordovician mass extinction by use of multivariate statistical analysis, and further to reveal its relationship to the evolutionary pattern of sponges during the crisis. This study will fill the gaps in the field of the background of the end-Ordovician mass extinction and the recovery and re-radiation in early Silurian.

奥陶纪末生物大灭绝是当今国际奥陶—志留系研究热点之一。不同海洋生物类群在应对这次危机事件中的表现各不相同。海绵作为一种底栖滤食性后生动物，对灾变期后海洋生态系统的构建具有重要意义。然而，囿于化石材料匮乏，海绵被认为在奥陶—志留纪过渡期内存在演化间断，对海绵在奥陶纪末大灭绝期间及其后残存—复苏等关键地史时期的具体表现尚知之甚少。本项研究拟以安徽南部奥陶—志留纪过渡期地层中的特异埋藏海绵动物化石为突破口，开展细致的系统古生物学和分支系统学研究，全面揭示奥陶纪末大灭绝前后海绵动物群的面貌及其系统发育关系；通过多学科交叉（古生物学、沉积学、埋藏学及古生态学），运用定量分析方法重建奥陶纪末大灭绝前后海洋生态系统的面貌，并揭示这一关键时期生物多样性演变与海洋生态系统之间的协同关系。这将是一项填补国际空白的工作，对于深刻揭示奥陶纪末大灭绝的实质并高精度地认识大灭绝及其后的残存与复苏具有重要意义。

奥陶纪末大灭绝是显生宙以来第一次大规模的生物灭绝事件，一直以来都是国际奥陶—志留系研究的前沿和热点之一。囿于化石记录稀少及埋藏条件限制，对于海绵动物历经奥陶纪末大灭绝的多样性演变型式尚知之甚少，相关研究十分薄弱。本项研究以安徽南部奥陶—志留纪过渡期地层中的特异埋藏海绵动物化石作为研究对象，开展系统古生物学、海绵动物宏演化研究，建立海绵属种多样性数据库；在此基础上通过学科交叉，对特异埋藏海绵动物群的埋藏机制进行探讨。项目执行期间，针对安徽南部及华南其他相区奥陶—志留纪过渡期地层开展了大范围野外考察和样品采集工作，积累了大量重要的原始材料；完成了主要研究剖面的化石鉴定、实验室成像、岩石及地球化学样品的实验室分析工作，阶段性成果相继发表。取得的主要研究成果包括：1）在华南奥陶—志留纪过渡期地层中发现最早的花骨海绵类化石，可将其化石记录提前300多个百万年；为探明此类海绵的系统演化提供了非常重要的材料，同时也为分子古生物学研究提供诸多关键信息，有助于较为精确地限定其祖先类群起源和演化的关键时间节点，大大提升了研究的精度。2）通过对华南奥陶—志留纪过渡期斑皮海绵类的新材料的研究，将斑皮海绵科由13属厘定为5属；首次报道了奥陶纪最末期地层中斑皮海绵类新属种，这一发现填补了奥陶—志留纪过渡期此类海绵化石记录的空白。3）通过研究首次在扬子台地西缘晚奥陶世地层中发现保存完好丰度和分异度均较高的凯迪期海绵骨针组合。这是目前全球除澳大利亚外唯一一个同时期的海绵骨针组合，二者可以很好地进行对比，具有重要的生物地层学意义。两个不同区域中产出的面貌相似的骨针组合也说明这两个环冈瓦纳板块的地区在晚奥陶世期间动物群之间存在一定程度的交流，具有重要的生物古地理意义。