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

腕足类是奥陶系和志留系（485419万年前）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。

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.