Distinguishing features: Holococcoliths with a narrow rim and a central structure comprising two or four blocks which typically incorporate a distal bridge-shaped structure which may extend into a spine; the blocks may be perforate.
| Daughter taxa: (blue => in age window 0-800Ma) | ||||
| | | | Holococcolith with narrow rim and central plate comprising four blocks, the largest two at either end and smaller two forming a transverse bridge. |
| | | | Holococcolith with narrow birefringent rim with transverse protrusions into the central area. The central plate consists of two perforate blocks joined along a transverse suture. The single perforation in each block may be closed due to overgrowth. In side view the narrow rim continues proximally; the central structure comprises two lateral blocks but occasionally a smaller two-part internal block may be visible. A variably developed spine extends distally and may be closed by a distal plug. All these structures observed in side view, generally appear as crystallographically distinct blocks. |
| | | | Holococcolith with narrow birefringent rim and central plate comprising two blocks crossed by four diagonal cross bars that are brightest at 0 degrees. joined along a transverse suture. The blocks may be perforate. |
| | | | Specimens not identified to species level |
Taxonomy:
Farinacci & Howe catalog pages: Owenia + * , ,
Distinguishing features: Holococcoliths with a narrow rim and a central structure comprising two or four blocks which typically incorporate a distal bridge-shaped structure which may extend into a spine; the blocks may be perforate.
Morphology remarks: O. hillii is considered by some to be a junior synonym of Isocrytallithus compactus Verbeek, 1976, although the illustrations provided by Verbeek were of side views, which differ from the side views of O. hillii (see Jeremiah, 1996, pl. 1, figs 3-4 and Burnett, 1998b, pl. 6.10, figs 4-5), i.e. cavate vs. relatively non-cavate/solid. The spines of the two species are, however, comparable. Other long-spined holococcoliths have been described from this stratigraphic interval, and I. compactus may be allied to the forms described as Anfractus harrisonii Medd, 1979 by Lambert (1987, pl. 14, figs 1-3).
A group of morphologically similar holococcoliths are classified here within the genus Owenia, though they were originally described in several different genera. They appear to represent an evolutionary lineage, although two of the forms may represent preservational conspecific morphotypes, and the boundaries between the species concepts may be gradational.
Geological Range:
Last occurrence (top): at top of Cenomanian Stage (100% up, 93.9Ma, in Cenomanian stage). Data source: Total of range of species in this database
First occurrence (base): in lower part of Aptian Stage (25% up, 123Ma, in Aptian stage). Data source: Total of range of species in this database
Plot of occurrence data:
Burnett, J. A. (1998). Upper Cretaceous. In, Bown, P. R. (ed.) Calcareous Nannofossil Biostratigraphy. British Micropalaeontological Society Publication Series. 132-199. gs Jeremiah, J. (1996). A proposed Albian to Lower Cenomanian nannofossil biozonation for England and the North Sea Basin. Journal of Micropalaeontology. 15(97-129): -. gs Kennedy, W. J. et al. (2000). Integrated stratigraphy across the Aptian-Albian boundary in the Marnes Bleues, at the Col de Pre _-Guittard, Arnayon (Drome), and at Tartonne (Alpes-de-Haute-Provence), France: a candidate Global Boundary Stratotype Section and Boundary Point for the base of the Albian Stage. Cretaceous Research. 21: 591-720. gs Lambert, B. (1987). Nannofossiles calcaires de l'Albien supérieur et du Vraconnien du Cameroun méridional. Cahiers de Micropaléontologie. 2(2): 33-60. gs Verbeek, J. W. (1976a). Upper Cretaceous calcareous nannoplankton from Ballon and Théligny in the type area of the Cenomanian stage (Sarthe, France). Proceedings of the Koninklijke Nederlandse Akademie van Wetenschappen. B79: 69-82. gsReferences:
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Owenia compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 22-7-2019
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