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

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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.