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标题：The late Eocene evolution of nummulitid foraminifer Spiroclypeus in the Western Tethys
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作者：GYÖRGY LESS ; ERCAN ÖZCAN
期刊名称：Acta Palaeontologica Polonica
印刷版ISSN：0567-7920
电子版ISSN：1732-2421
出版年度：2008
卷号：53
期号：2
页码：303-316
DOI：10.4202/app.2008.0211
语种：English
出版社：Institute of Paleobiology PAS
摘要：Megalospheric forms of Priabonian Spiroclypeus of the Western Tethys were morphometrically investigated. Based on the reduction of the average number of undivided, post-embryonic chambers, the investigated populations are grouped into two successive, phylogenetically linked species, S. sirottii sp. nov. and S. carpaticus. The evolution is also demonstrated by the increase of the number of secondary chamberlets in particular chambers, by the increase of the diameter of the first two whorls and by that of the size of the proloculus, although the latter turned out to be also ecologically controlled. This evolution is supported by the stratigraphic succession of populations in the Mossano section (N Italy) and by the change of accompanying fossils. Lacking in upper Bartonian beds, the first appearance of genus Spiroclypeus seems to be synchronous with the beginning of the late Eocene. The newly described S. sirottii is associated with Heterostegina reticulata mossanensis and orthophragmines containing forms of middle Eocene acme, both marking the lower part of the Priabonian. Meanwhile S. carpaticus co-occurs with H. gracilis and/or with orthophragmines characteristic of the upper part of the Priabonian. We suppose that the Spiroclypeus sirottii–carpaticus lineage is restricted to the Priabonian. Thus, Spiroclypeus sirottii is a zonal marker for the Shallow Benthic Zone (SBZ) 19 (early Priabonian) while S. carpaticus indicates the SBZ 20 (late Priabonian).
关键词：Foraminifera;Nummulitidae;Spiroclypeus;biometry;evolution;stratigraphy;Eocene