Taxonomic descriptions and evolutionary implications of Middle Eocene pennate diatoms representing the extant genera Oxyneis, Actinella and Nupela (Bacillariophyceae)
Methods – Both oxidized preparations and whole-rock mudstone samples from the Giraffe Pipe core were examined with light and scanning electron microscopy for diatom remains.
Key results – Species belonging to the genera Actinella F.W.Lewis, Oxyneis Round and Nupela Vyverman & Compère are described from the Giraffe Pipe sediments. Oxyneis apporrecta is a unique species with valves that are centrally constricted, inflations midway between the center and apices, and protracted and rostrate apices. Actinella giraffensis is a small taxon that lacks a highly complex head pole, and is most closely related to a species known today only from the highlands of New Zealand. Nupela mutabilis has variably shaped valves possessing a raphe and unique areolae characteristic of this genus. These findings represent the first known fossils for both Oxyneis and Nupela, and the oldest record for Actinella.
Conclusions – None of the species are known from extant floras and are therefore considered extinct. However, the morphological features they present, including the structure of the areolae, raphe, rimoportula and girdle bands, share pronounced affinities with modern congeneric taxa. The well-developed raphe found on Nupela mutabilis confirms that the evolution of this structure dates to at least the Middle Eocene, and supports the hypothesis that it may be older than the Paleocene.
Document Type: Regular Paper
Publication date: 2010-11-01
Plant Ecology and Evolution (a continuation of Belgian Journal of Botany, incorporating Systematics and Geography of Plants) is an international journal devoted to ecology, phylogenetics and systematics of all 'plant' groups in the traditional sense (including algae, cyanobacteria, fungi, myxomycetes), also covering related fields such as comparative and developmental morphology, conservation biology, ecophysiology, evolution, phytogeography, pollen and spores, population biology, and vegetation studies. It is published by the Royal Botanical Society of Belgium and the Botanic Garden Meise and contains original research papers, review articles, checklists, short communications and book reviews.
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