Survival and re-diversification of pentameride brachiopod fauna from Late Ordovician to early Silurian

腕足类作为奥陶纪和志留纪(距今48.5419亿年前)的一组优势海洋贝类，在晚奥陶世-志留纪早期经历了温室-冰库气候变化，经历了剧烈的多样性波动。五味子菌群在晚奥陶世经历了一次中等程度的辐射，但在晚奥陶世大灭绝时几乎灭绝，减少到单一的Brevilamnulella属。到志留纪早期，五氯化物迅速辐射，主宰浅海。因此，五倍体的起源和早期进化构成了一个几乎完全灭绝但迅速重新多样化的惊人案例。*最早的志留纪五星藻表现出快速的形态变化，以适应广泛的水深和底质条件，表现为三个主要类群(维吉亚类、斯特兰迪亚类和三叠体)。志留纪早期最古老的Stricklandia和Clorinda在形态上与Brevilamnulella相似，年轻的Stricklandias进化为具有较宽Hingeline的大贝壳，以适应相对深水、柔软的泥质底质。海龙保留了一个相对较小的球状外壳，专门生活在低能量、深水、外陆架的环境中。早志留世从Brevilamnulella到Brevilamnulella的五星藻的多样性被解释为从浅层、高能量环境到深而安静的外陆架环境的广泛生态位的快速勘探，由于晚奥陶世的大规模灭绝事件，这些生态位基本上是“空的”。本研究将考察赫南提布列姆海藻和志留纪最早的五星类之间的形态差异，以确定它们与祖先布氏线虫和志留纪最早的维吉亚目、斯特兰迪亚类和环虫类之间的系统发育关系，并探索与物种形成有关的生态因素。*为了验证灭绝幸存者Brevilamnulella产生了大量五足腕足动物成为志留纪主要“海壳”的假设，与几个国际同事的研究合作将有助于获得来自加拿大、英国、北格陵兰岛和南中国的关键五元体收藏品，范围从奥陶纪晚期到志留纪早期。将使用多种技术方法(连续切片、模具和铸件以及显微CT扫描)来建立可靠的形态数据库。然后将使用多变量和分支分析方法对数据进行分析，以揭示进化趋势、系统发育关系和古生态意义。这种类型的研究将有助于揭示当全球生物多样性经历剧烈的繁荣-萧条-复苏周期时的进化过程。**

As a group of dominant marine sea shells in the Ordovician and Silurian periods (485419 million years ago), brachiopods experienced drastic diversity fluctuations through greenhouse-icehouse climate changes in the Late Ordovician-early Silurian. The Pentameridine group underwent a moderate radiation during the Late Ordovician but became nearly extinct during the Late Ordovician Mass Extinction, reduced to a single genus Brevilamnulella. By the early Silurian, pentameride radiated rapidly to dominate the shallow seas. Thus the origin and early evolution of the pentameridines constituted a striking case of near total extinction but rapid re-diversification. *** Earliest Silurian pentamerides showed rapid morphological transformations to adapt to a wide range of water depth and substrate conditions, represented by three major groups (the virgianids, stricklandiids, and clorindids). The oldest Stricklandia and Clorinda in the earliest Silurian show morphological similarities to Brevilamnulella, with younger stricklandioids evolving towards a large shell with a wide hingeline to adapt to relatively deep-water, soft muddy substrate. The clorindioids retained a relatively small, globular shell to specialize in living in low-energy, deep-water, outer-shelf environment. The early Silurian diversification of pentamerides from Brevilamnulella is interpreted as rapid exploration of a wide range ecological niches from shallow, high-energy settings to deep and quiet outer-shelf environments, left largely “empty” by the Late Ordovician mass extinction event.*** The great morphological plasticity in earliest Silurian pentamerides has made it difficult to quantitatively study their initial diversification. This study will examine the morphological variability among the Hirnantian Brevilmnulella and the earliest Silurian pentamerides to determine their phylogenetic relationships among the ancestral Brevilamnulella and the earliest Silurian virgianids, stricklandioids, and clorindioids, and to explore the ecological factors related to speciation. *** To test the hypothesis that the extinction survivor Brevilamnulella gave rise to a multitude of pentameride brachiopods that became the dominant Silurian “sea shells”, research collaborations with several international colleagues will help gain access to key pentameride collections from Canada, the UK, North Greenland, and South China, ranging from the Late Ordovician to early Silurian. A multi-technique approach (serial sectioning, moulds and cast, and micro-CT scanning) will be used to build a reliable morphological database. The data will then be analyzed using multivariate and cladistic methods to reveal evolutionary trends, phylogenetic relationships, and paleoecological implications. This type of study will help shed light on the evolutionary processes when global biodiversity undergoes a drastic boom-bust-recovery cycle. **