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

腕足类是奥陶纪和志留纪（距今4.85 - 4.19亿年）的优势海洋贝类，在晚奥陶世-早志留世温室-冰室气候变化中经历了剧烈的多样性波动。Pentameridine组在晚奥陶世期间经历了适度的辐射，但在晚奥陶世大灭绝期间几乎灭绝，减少为单一的Brevilamnulella属。到志留纪早期，五聚体迅速辐射到浅海。因此，pentameridines的起源和早期进化构成了一个几乎完全灭绝但迅速重新多样化的惊人案例。 最早的志留纪pentamerides表现出快速的形态转变，以适应广泛的水深和基质条件，由三个主要群体（virgianids，stricklandiids和clorindids）代表。最古老的Stricklandia和Clorinda在最早的志留纪表现出与Brevilamnulella形态上的相似性，年轻的stricklandioids向具有宽铰链线的大壳进化，以适应相对深水，柔软的泥泞基质。clorindioids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。从Brevilamnulella的pentamerides的志留纪早期的多样化被解释为快速探索广泛的生态位从浅，高能量的设置深，安静的外大陆架环境，留下很大程度上是“空”的晚奥陶纪大规模灭绝事件。 志留纪早期五聚体的巨大形态可塑性使得定量研究其初始多样性变得困难。本研究将通过对Hirnantian Brevilmnulella和志留纪最早期五倍体之间形态差异的研究，确定其与志留纪最早期的virgianids、stricklandioids和clorindioids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产生了大量五倍体腕足动物成为志留纪主要“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，格陵兰北部和中国南方的关键五倍体收藏品，从晚奥陶纪到志留纪早期。将采用多技术方法（连续切片、铸模和铸型以及显微CT扫描）建立可靠的形态学数据库。然后，将使用多变量和分支的方法来分析数据，以揭示进化趋势，系统发育关系，和古生态学的影响。这种类型的研究将有助于揭示全球生物多样性经历剧烈繁荣-萧条-恢复周期时的进化过程。

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.