British carboniferous bryozoan biogeography

Abstract

The geographical and temporal distributions of the British Carboniferous Bryozoa have been determined, incorporating data from fieldwork (including localities in Scotland, North England, North Wales, South Wales, and Avon), museum collections, and literature searches. A total of 126 species has been recognised, though further work may reveal some synonymies within this list. The forty species collected during the fieldwork have been identified by reference to previous taxonomic work; most species can be assigned to established taxonomic descriptions, but two new species, Rhombopora bancrofti and Polypora hexagonaria, are proposed, and the descriptions of Rhombopora incrassata and Rhombopora similis are emended. The applicability of Student's t-test to the morphometric analysis of Carboniferous bryozoan species has been studied, and a computer program written to perforin this task, incorporating a database of species measurements. A new statistical method, the division t-test, is presented in this thesis; this method is useful in comparing the relative ratios of bryozoan colony parameters. Both the t-test and the division t-test were found to be of use in identifying bryozoan species. Analysis of the bryozoan faunas in nine regional areas of Britain has been made using the Simpson and Jaccard coefficients of similarity. The resulting coefficients are consistent with the limited distribution capability of many bryozoan taxa, and also match with the known palaeogeography and palaeocurrents of the Carboniferous of northwest Europe. Plots of species diversity against geographical distribution show a similar pattern to that produced by Tertiary non-planktotrophic larvae-bearing neogastropods. Further, additional plots of species diversity against species longevity produced a pattern consistent with normal background extinction events. A study of bryozoan morphology between different areas and different stages within the Carboniferous indicated that species showed no measurable temporal evolutionary or lateral geographical changes through the Lower Carboniferous. Rather, local environmental stresses are the major architects of bryozoan colony morphology.