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

腕足类是奥陶系—志留系（4.85—4.19亿年前）占优势的海洋贝壳类，在晚奥陶世—早志留世的温室—冰室气候变化中经历了剧烈的多样性波动。Pentameridine组在晚奥陶世经历了适度的辐射，但在晚奥陶世大灭绝期间几乎灭绝，减少到一个单一的属Brevilamnulella。到志留纪早期，五聚氰胺迅速扩散到浅海。因此，pentameridines的起源和早期进化构成了一个几乎完全灭绝但又迅速重新多样化的惊人案例。志留纪早期的五聚亚胺类为适应广泛的水深和底物条件，表现出快速的形态转变，主要有三大类（virgianids、stricklanddiids和clorindiids）。志留纪早期最古老的Stricklandia和Clorinda在形态上与Brevilamnulella相似，较年轻的stricklandioids进化为具有宽hingeline的大壳，以适应相对深水，柔软的泥质基质。氯虫保留了一个相对较小的球形外壳，专门生活在低能量、深水、外大陆架环境中。早志留纪Brevilamnulella的五amerides多样化被解释为对广泛生态位的快速探索，从浅层、高能环境到深层、安静的外大陆架环境，在晚奥陶纪大规模灭绝事件中留下了很大的“空白”。早期志留纪五聚亚胺具有很大的形态可塑性，这给定量研究其初始多样化带来了困难。本研究将通过对Hirnantian Brevilmnulella和志留纪早期五聚虫的形态变异进行研究，以确定其祖先Brevilamnulella与志留纪早期virgianids、stricklandiids和clorindiids之间的系统发育关系，并探讨与物种形成相关的生态因素。为了验证灭绝幸存者Brevilamnulella产生了大量的五聚体腕足动物，并成为志留纪的主要“海贝壳”的假设，与几位国际同事的研究合作将有助于获得来自加拿大，英国，北格陵兰和华南的关键五聚体收藏品，范围从晚奥陶纪到早志留纪。多技术方法（连续切片，模具和铸造，微ct扫描）将被用来建立一个可靠的形态学数据库。然后，这些数据将使用多变量和分支学方法进行分析，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阐明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 (485-419 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.