Lead supervisor: Nicholas J. Butterfield, Earth Sciences
Co-supervisor: Oscar Branson, Earth Sciences; Ekhard Salje, Earth Sciences
Brief summary:
Systematic interrogation of the mineralogy and microstructure of Edicacaran-Recent sponge spicules will yield a fundamentally new account of both spiculogenesis and diagenesis in basal metazoans
Importance of the area of research concerned:
Sponges are the simplest of all extant metazoans and have a rich Phanerozoic record of fossil spicules. Although commonly disarticulated and diagenetically altered, these biomineralized hardparts can be reliably assigned to higher-order clades via their diagnostic morphologies – or so it has always been assumed. Petrographic analysis reveals a confusing mosaic of mineralogical, microstructural and morphological characters that undermines much of their conventional taxonomic treatment. Some of this reflects the extinct character combinations exhibited by underlying stem-groups, but it is also important to recognize the potential for both secondary alteration and convergent evolution. This project will systematically investigate the fossil record of spiculate sponges, taking particular aim at modes of spiculogenesis (as reflected in spicule mineralogy/microstructure), and the taphonomic pathways responsible for their disparate modes of preservation. Such reassessment is likely to overturn longstanding views of early sponge evolution.
Project summary :
The project will investigate the mineralogy, microstructure and morphology of fossil sponge spicules, with a particular focus on Palaeozoic and Mesozoic taxa. Most research materials will be sourced through the published literature and existing museum collections (e.g., Sedgwick, NHM, Smithsonian), but with opportunities to extend this via independent field work. Microstructural comparison with living counterparts and documentation of post-mortem alteration effects (e.g., from amorphous to crystalline phases and later-stage diagenesis) will include work with in-house aquarium specimens - in concert with high resolution petrographic, XRD, Raman, FTIR, AFM and acoustic emission techniques. The comprehensively expanded character matrix emerging from this study will be used to explore the deep phylogenetic relationships of total-group sponges.
What will the student do?:
The student will conduct a comprehensive study of the mineralogy, microstructure and morphology of fossil sponge spicules, with an eye to reconstructing early modes of spiculogenesis/biomineralization and their evolutionary trajectories. Primary data collection will include deep searches through museum collections (with a focus on the NHM and Smithsonian), followed by preparation and high-resolution analysis of individual spicules. Given the widespread preservation of fossil spicules in calcite, the study will also investigate the details of biomineralization in living calcarean sponges, with a focus on the transition from amorphous calcium carbonate to biocalcite. Fossil spicules have of course been overprinted by later-stage diagenetic processes including conversion to geocalcite, recrystalization, silicification, pyritization and/or dissolution. These phenomena will be interrogated both as tools for recovering original mineralogy and microstructure, and to understand sponge taphonomy more generally. The additional characters provided by this work will prompt a major reassessment of early sponge evolution.
References - references should provide further reading about the project:
Botting, J.P. & Butterfield, N.J. 2005. Reconstructing early sponge relationships by using the Burgess Shale fossil Eiffelia globosa, Walcott. Proceedings of the National Academy of Sciences of the United States of America 102, 1554–1559.
Gilbert, P.U.P.A., et al. 2022. Biomineralization: integrating mechanism and evolutionary history. Science Advances 8, eabl9653.
Botting, J.P. & Muir, L.A. 2018. Early sponge evolution: A review and phylogenetic framework. Palaeoworld 27, 1–29.
Applying
You can find out about applying for this project on the Department of Earth Sciences page.