Barker, Michael John (1976) A stratigraphical palaeoecological and biometrical study of some English Bathonian Gastropoda (especially Nerineacea. Doctoral thesis, Keele University.

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Abstract

The stratigraphy of the Bathonian White Limestone Formation (M. Jurassic: Subcontractus - Retrocostatum zones) has been re-examined and the Formation is divided into three Members instead of the previous two; the new Excavata Beds at the base, the Ardley Beds and the Bladon Beds at the top. These are based upon gastropod subzones using species of the Nerineid genus Aphanoptyxis -
A. excavata sp. nov., A. ard1eyensis and A. biadonensis. A more precise internal correlation and zonation of the White Limestone, which agrees with the known ammonite distribution both in the White Limestone and elsewhere, is thereby achieved.
The abundant gastropod Eunerinea arduennensis has previously been mis-identified as Eu. eudesi1 and considerable taxonomic changes amongst representatives of the genus Bactroptyxis and other Nerineacean genera are proposed. A new genus Zenoplocus (type-species Zenoplocus microplicatus gen. et sp. nov.) is described together with three other new gastropod species; A. excavata, A. compressa and Fibula reticulata. Rigauxia, Endiaplocus and Fi buloptyxis, genera previously best known from the French Bathonian, are shown to be abundant in the English Bathonian.
Biometric analyses indicate that growth in Bathonian Nertneids was essentially isometric. A short evolutionary lineage from A. excavata through A. cf. lanqrunensis to A. ardleyensis has been documented from the Excavata and Ardley Beds and computer studies using multivariate stepwise discriminant analysis have facilitated species descrimination.
The helically colled duct system in the digestive gland/gonad in Nerineid gastropods has been described. This together with a new interpretation of the biological function of Nerineid folds suggests that these gastropods occupied several ecological niches (both infaunal and epifaunal) in carbonate substrates but were essentially deposit feeders. The stages of epibiontic colonisation, shell destruction and diagenesis have been outlined. Laevinerinea and Aptyxiella are shown to possess crossed-lamellar shell microstructures.
It is suggested that the Nerineacea may best be regarded as primitive Caenogastropods (Prosobranchs) and problems of their further classification are disucssed.

Item Type: Thesis (Doctoral)
Subjects: Q Science > QE Geology
Divisions: Faculty of Natural Sciences > School of Geography, Geology and the Environment
Depositing User: Lisa Bailey
Date Deposited: 09 May 2019 08:09
Last Modified: 09 May 2019 08:09
URI: http://eprints.keele.ac.uk/id/eprint/6293

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