This study of the Maastrichtian (latest Cretaceous, 71–65 Ma) species of Manumiella Bujak and Davies 1983 in the James Ross Basin, Antarctic Peninsula is focussed on the biostratigraphical and palaeoecological significance of this peridinioid dinoflagellate cyst genus, in particular with reference to oceanic changes associated with the Cretaceous/Tertiary (KT) boundary. New palynological analyses throughout the upper part of the latest Maastrichtian López de Bertodano Formation on Seymour Island has resulted in the emendation of Manumiella to include the presence of a mesophragm, and the formal description of Manumiella bertodano sp. nov. A morphological continuum exists between species of Manumiella, but the apparent biostratigraphical significance of the end-member morphologies emphasises the need for consistent and distinct species concepts. Consequently, a new botanical key has been devised based on the morphological features of Manumiella bertodano sp. nov., Manumiella conorata [Stover, L.E., 1973. Palaeocene and Eocene species of Deflandrea (Dinophyceae) in Victorian coastal and offshore basins, Australia. In: Glover, J.E., Playford, G. (Eds.), Mesozoic and Cainozoic Palynology: Essays in Honour of Isabel Cookson. Geological Society of Australia, Special Publication vol. 4, 167–188.] Bujak and Davies 1983, Manumiella druggii [Stover, L.E., 1973. Palaeocene and Eocene species of Deflandrea (Dinophyceae) in Victorian coastal and offshore basins, Australia. In: Glover, J.E., Playford, G. (Eds.), Mesozoic and Cainozoic Palynology: Essays in Honour of Isabel Cookson. Geological Society of Australia, Special Publication vol. 4, 167–188.] Bujak and Davies 1983, Manumiella seelandica (Lange, D., 1969. Mikroplankton aus dem Fischton von Stevns-Klint auf Seeland. Beiträge zur Meereskunde, 24–25, 110–121.) Bujak and Davies emend. Firth 1987 and Manumiella seymourensis Askin 1999. Manumiella druggii and Manumiella seelandica are retained as separate species. The key has been successfully tested on the well-preserved dinoflagellate cyst assemblages from the uppermost López de Bertodano Formation on Seymour Island, resulting in a clear biostratigraphy based on an existing preliminary scheme. Manumiella seymourensis is prominent in the lowermost part of the succession, and the uppermost part of the range of this species overlaps with that of Manumiella bertodano sp. nov. The latter species ranges into the latest Maastrichtian, where it co-occurs with Manumiella conorata and Manumiella seelandica. Manumiella druggii is confined to the uppermost part of the succession examined. Abundance spikes of Manumiella immediately prior to the KT boundary in this succession have also been recognised globally, and may be related to short-term regressions and/or ocean cooling before the KT event
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