湖北恩施中奥陶统大湾组棘皮动物系统古生物学和古生态学

Echinoderms are common members in the marine benthic ecosystem. They were important contributors for building a local benthic ecologic community during the Great Ordovician Biodiversity Event (GOBE) due to a wide range of adaptation capacity and rapid origination of new taxa within the Echinodermata. In addition, echinoderm ossicles after disarticulation can form a coherent carbonate rock mass that leads to changes of local substrate conditions and attracts larval settlement and recruitment during a faunal succession. Most echinoderms exhibit pentaradial symmetry, which is unique among invertebrates, but its origin is still unclear because articulated specimens are relatively scarce in the fossil record. Preservation of complete echinoderms requires both a low-energy flow regime setting and a rapid burial event. During the past three years team members have recovered a rich echinoderm fossil assemblage from the Ordovician Dawan Formation near Enshi area, Hubei Province. Up to date, a total of 111 articulated specimens, including new species of cystoids, are collected. In particular, curved cystoid stems are seldom mentioned in previous Chinese studies; thus, this rare find provides not only the new evidence of the echinoderm biodiversity during the GOBE in South China but also new information allowing us to understand better the construction of early cystoid body plan and their evolutionary roadmaps. Furthermore, studying the functional morphology of cystoids we can interpret better the palaeoecological details of specific individuals and the palaeogeographic distribution of some endemic groups.

棘皮动物是海洋底栖生态系统中的常见分子，在奥陶纪生物大辐射事件期间多个新阶元的起源分化以及广适性而成为底栖生态群落建造的重要组成分子，其散落的骨板能快速固结成岩可改变碳酸盐岩海底底质并渠导生态群落的演替；多数棘皮动物具五辐对称性，这种特殊体型构建方式的起源机制尚不清晰，在很大程度上要归因于骨板散乱堆积的棘屑滩常见而完整个体化石保存不易，仅低能水体或快速埋葬的沉积环境利于骨板愈合方式保存。课题组近三年来从湖北恩施奥陶纪大湾组中采获丰富的棘皮动物化石，其中比较完整的标本共111块，初步鉴定结果显示这些化石中不乏海林檎类的新属种，其中保存弯曲的海林檎茎化石是前人研究中极少见及的。这一稀缺化石记录素材不仅显示了华南奥陶纪生物大辐射过程中棘皮动物多样性的系统古生物学实证材料，还有助于了解早期海林檎形态构建机制和特化方向，藉此对其形态-功能学分析可复原早期海林檎类型个体古生态学细节以及生物古地理分布。

海林檎是奥陶纪生物大辐射时期出现的重要后生动物底栖固着类群之一，对陆表海群落的构建方式影响显著，其生物多样性和古地理分布是解析生物-环境协同演化的实证材料。皖南泾县下奥陶统仑山组呈现钙质微生物岩叠层石-Hemicosmite-Paracrinus群落，代表奥陶纪生物大辐射早期海林檎和海百合个别属种特有的席底生态位。中奥陶世的海林檎在中国多个构造区分布，生物多样性达到最高且多呈聚集式保存，其多赋存于浅海灰岩相，指示海林檎的密集生长需要较高清澈度的海底条件。首次在鄂西宜昌地区上奥陶统桑比阶庙坡组泥岩中发现海林檎Cheirocrinus，其生态位属陆表海碳酸盐岩台地上的凹陷区。上扬子陆表海区远岸区的宜昌宜黄1井上奥陶统的生物-岩相地层序列呈现明显相关性，包括棘皮动物等壳相生物群组成受海洋滞流模式以及生物大灭绝事件期的水体增氧事件控制，底质条件的变化直接导致后生动物生产力和化石结构的更替。中国原有的海林檎的化石记录限于奥陶系，我们首次发现扬子区志留系和龙门山地区泥盆纪的海林檎化石，对诠释中国古生代海林檎的生物多样性演变和地理分布提供了新证据，总体表现为奥陶纪末的灭绝事件之后海林檎属种呈现数量和丰度明显减少，生态域偏窄，更趋向于珊瑚-层孔海绵礁滩相栖居。.扩展化石采集的地点和层位获得大量精美标本，为重建中国古生代棘皮动物多样性提供系统古生物学和古地理分布的新资料。上扬子区兰多维列世埃隆阶陆表海浅水碳酸盐岩沉积区的古生态指标差异造成花瓣海百合科生物多样性分布的不均一性，高分异度和丰度以及演化成种中心集中于黔北珊瑚-层孔海绵礁相建造区。首次在掸泰区泥盆系何元寨组发现中国保存完好的古生代海胆和海蕾新种，以及组成个体发育序列的幼枝海百合新种的400多枚化石。在华北板块下二叠统太原组含泥灰岩中发现4个海百合新种，其动物群特征分子在种级层次上有别于同期全球其它板块。以上成果细化了中国古生代数个地质时代节点的生物多样性演变过程。