Planktic foraminiferal tests and their morphology have been the subject of extensive study for biostratigraphy and palaeoenvironmental reconstructions. Iterative evolution of morphological designs and correlations between morphology and environmental parameters suggest either fundamental intrinsic constraints on form , or a functional control, or both. Yet the adaptive significance of the test morphologies in terms of these constraints has never been rigorously explored, and is the focus of this thesis. The developmental and growth constraints delimiting the scope of action for evolution were determined through ontogenetic reconstructions based on SRXTM scans. Differences in growth patterns between the globigerinid and globorotalid groups imply a different potential for diversification. Different metabolic processes dominate growth at different stages of ontogeny due to changes in surface area-to-volume ratios, so mechanisms of evolution responding to environmental factors may change depending on when they occur in ontogeny. Imposed on these are constructional considerations, which were gauged through estimation of coiling patterns through ontogeny from the reconstructions. Coiling in early ontogeny is constrained across all species to maximise lateral growth. From the neanic stage, changes in coiling occur to accommodate new chamber shapes, and are modulated by the migration of the aperture. Developmental processes of evolution must therefore operate within this framework. Computational fluid dynamic simulations were used to assess the functional role of the test in adjusting settling velocity, by varying morphological and water parameters independently. The range of evolutionary options open to foraminifera is a result of trade-offs between changes in size, shape and density, and environmentally required fluctuations can easily be accommodated by the natural within-population variability. The findings of this thesis imply that, in the compromise between function and constraints acting with the environment to define adult morphology and diversification, intrinsic factors are likely to play a more important role than function in plank tic foraminifera.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:628998 |
| Date | January 2013 |
| Creators | Caromel, Aude Genevieve Marcelle |
| Publisher | University of Bristol |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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