Diversification patterns and body plan evolution of glass sponges (Porifera: Hexactinellida) throughout the Phanerozoic, and a critical evaluation of evolutionary inference methods

玻璃海绵（Porifera门：Hexactinellida纲）是一种重要的生态动物，但在全球范围内只有少数专家对其进行了研究。它们有着悠久而丰富的化石记录，是中生代重要的珊瑚礁建造者，但许多已灭绝的分类群与现存的分类群之间的关系在很大程度上仍然难以捉摸，而且整个显生宙的种群多样化动态仍然知之甚少。Hexactinellida的分子系统发育和分化时间估计与基于形态学的系统和化石记录基本一致。然而，他们也表明，六边形身体结构的进化，即海绵支撑骨骼的不同结构类型，可能比最初想象的要复杂得多。不幸的是，一些系统发育上最重要的分类群还没有被取样用于分子研究，这使得不可能消除骨骼进化的可能情景之间的歧异，并且使该群体的更高层次的系统分类在很大程度上悬而未决。该项目旨在扩大现有的分子数据集，并产生一个分辨率高、时间校准的玻璃海绵系统发育，与化石记录的数据相结合，将形成以下基础：a)构建一个修订的类群分类，这将有助于整合古生物学和新学研究；b)重建宏观进化多样化动力学（进化谱系的差异起源和灭绝率）；（以及它们的成因）在显生宙的整个种群中，迄今为止还没有对任何多孔岩分类单元进行过这样的研究。该项目特别关注不同的骨骼结构类型是如何、为什么以及何时进化的，这可以为Porifera和后生动物的身体结构进化的可塑性提供新的见解。系统发育重建、分化时间估计、表型特征进化重建和多样化率模式重建等一系列最先进的方法正在被探索，并根据它们在进化生物学中的一般用途进行严格的比较和评估。该项目由慕尼黑大学古生物与地球生物学系地球与环境科学系分子地球与古生物实验室进行。

Glass sponges (phylum Porifera: class Hexactinellida) are an ecologically important but understudied group of deep-sea animals with only a handful of experts worldwide. They have a long and rich fossil record and were important reef-builders in the Mesozoic, but relationships of many extinct to extant taxa remain largely elusive and the diversification dynamics of the group throughout the Phanerozoic are still poorly understood. Molecular phylogenies and divergence time estimations of Hexactinellida show a generally good agreement with morphology-based systems and the fossil record. However, they also suggest that the evolution of hexactinellid body plans, i.e. the different construction types of the sponges' supporting skeletons, might have been more complex than originally thought. Unfortunately, some of the phylogenetically most important taxa have not been sampled yet for molecular studies, which makes it impossible to disambiguate between possible scenarios of skeletal evolution, and leaves the higher-level systematics of the group largely unresolved. The project aims at expanding the existing molecular dataset and produce a well-resolved, time-calibrated phylogeny of glass sponges, which, in combination with data from the fossil record, will then form the basis for a) constructing a revised classification of the group that will facilitate integrating paleo- and neontological research, and b) reconstructing macroevolutionary diversification dynamics (differential origination and extinction rates of evolutionary lineages, and their causes) of the group throughout the Phanerozoic, which has never been done so far for any poriferan taxon. The project especially focusses on how, why, and when the different skeletal construction types evolved, which could provide new insights into plasticity of body plan evolution in Porifera and Metazoa in general. A wide range of state-of-the-art methods for phylogeny reconstruction, divergence time estimation, reconstruction of phenotypic character evolution, and reconstruction of diversification-rate patterns are being explored and critically compared and evaluated with respect to their general usefulness for evolutionary biology. The project is carried out at the Molecular Geo- and Palaeobiology Lab, Dept. of Earth- and Environmental Sciences, Palaeontology & Geobiology, LMU Munich.