8th International Nannoplankton Association Conference


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Michael Knappertsbusch:
3D-animated views of the morphological evolution of the coccolithophorid Calcidiscus leptoporus from the Early Miocene to Recent

For the first time, animated diagrams are prepared to illustrate the complex microevolutionary trends and the inferred phylogeny of the coccolithophorids Calcidiscus leptoporus and C. macintyrei from the Early Miocene to the Quaternary. These patterns were derived from extensive morphometric measurements and bivariate frequency diagrams of coccolith diameters and number of elements in the distal shields. A total of nine informal morphotypes, S, I, L, F, A, B, C, D and E, are distinguished. Speciation patterns, such as cladogenesis and phyletic divergence, were observed, but there is also stasis over prolonged time-intervals. Similar coccoliths developed repeatedly at stratigraphically-distant intervals, leading to taxonomic complications. Using two different analytical approaches, a tentative phylogeny was constructed suggesting, that they belong to one extant species and several extinct species. The extant species is Calcidiscus leptoporus, which comprises the living morphotypes S, I, L and F, and one extinct morphotype, E. Morphotype S is the most conservative one, which originated from an unknown ancestor during the Early Miocene or earlier, while morphotype I originated from S during the Early Miocene. Morphotypes L and E separated from I during the Late Miocene. An extinct lineage is proposed, which includes morphotypes C, D, A and B, which all produced large coccoliths, except morphotype B which is small. Morphotypes C, D and A are very similar to a coccolith that specialists call Calcidiscus macintyrei but, with the presented phylogenetic model, they may belong to separate species with similar morphology. Morphotype C developed from morphotype I during the Early Miocene and is the precursor to an extra large morphotype, D, and two other morphotypes, A and B. All three forms separated from morphotype C by pronounced cladogenetic events during the Late Miocene and Pliocene and hence may represent separate species. Morphotypes A and B are supposed to belong to an extinct morphocline and may be ecophenotypes of one species. Due to the lack of palaeoenvironmental and biogeographic observations in the past, it cannot be discounted that all morphotypes found in this investigation represent ecovariants of one species. With the present status of knowledge, it is not possible to propose a binding differential diagnosis in the plexus C. leptoporus-C. macintyrei, which would allow differentiation between species at each point in space and time. It is hoped that this study stimulates further morphometric and phylogenetic studies to arrive at a more profound understanding of species in palaeontology, and biology in general.


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 [Division of Micropalaeontology] [Department of Geosciences] [Bremen University]

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Copyright © 2000, most recent revision July 24, 2000

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