Coccolithus gigas


Ancestry: Coccolithophores -> Coccolithales -> Coccolithaceae -> Coccolithus -> C. gigas group -> Coccolithus gigas
Sister taxa: C. gigas, C. hulliae, C. opdykei, C. mutatus, C. staurion,

Short diagnosis: Very large (~>15µm) Coccolithus-like coccolith with narrow central area crossed by broad diagonal bars.


Taxonomy:

Citation: Coccolithus gigas Bramlette & Sullivan, 1961
Rank: Species
Basionym: Coccolithus gigas Bramlette & Sullivan, 1961
Synonyms: Sullivania gigas (Bramlette & Sullivan, 1961) Varol, 1992
Chiasmolithus gigas (Bramlette & Sullivan, 1961) Radomski, 1968
Notes & discussion: Traditionally included in Chiasmolithus, but the species does not fit readily in either of the two groups of Chiasmolithus species. Bown & Newsam (2017) observed a lineage from Coccolithus staurion to C. gigas and so concluded that it should be transferred from Chiasmolithus to Coccolithus.

Specimens with rotated, asymmetric cross-bars also occur but may have the same stratigraphic range.

Farinacci & Howe catalog pages: Coccolithus gigas + *

Short diagnosis: Very large (~>15µm) Coccolithus-like coccolith with narrow central area crossed by broad diagonal bars.


Morphology remarks: C. gigas has a distinctly wider shield than other members of the bidens group but clearly has bidens-type crossbars. Gartner (1970) and Romein (1979) suggest that it evolved from C. solitus, this would suggest that the distal shield widened but the central area stayed more or less the same size.

Geological Range:
Last occurrence (top): within NP15b subzone (44.12-45.49Ma, top in Lutetian stage). Data source: Perch-Nielsen 1985b
First occurrence (base): within NP15b subzone (44.12-45.49Ma, base in Lutetian stage). Data source: Perch-Nielsen 1985

Plot of occurrence data:

References:

Bramlette, M.N. & Sullivan, F.R., (1961). Coccolithophorids and related nannoplankton of the Early Tertiary in California. Micropaleontology, 7(129-188).

Perch-Nielsen, K., (1985). Cenozoic calcareous nannofossils. In: Bolli, H.M., Saunders, J.B. and Perch-Nielsen, K. (Editors), Plankton Stratigraphy. Cambridge University Press, Cambridge, pp. 427-555.

Radomski, A., (1968). Pozimy nannoplankton wapiennego w Paleogenie Polskich Karpat Zachodnich [Calcareous nannoplankton zones in Palaeogene of the western Polish Carpathiansl. Rocz. Polsk. Towarz. Geol., 38: 545-605.

Varol, O., (1992). Sullivania a new genus of Palaeogene coccoliths. Journal of Micropalaeontology, 11: 141-150.


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Coccolithus gigas compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 20-8-2017

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Comments (1)

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Ronald W. Morin (Morin Biostratigraphic Studies, US)
You have placed Chiasmolithus gigas in the Chiasmolithus consuetus group (bars undivided in XPL or crossed polarized light). However, the majority of your images of C. gigas show a clear median extinction line. In addition, the holotype of C. gigas (in XPL) appears to show a hint of a median extinction line in the bottom-left bar. It would be helpful if the holotype of C. gigas could be re-photographed to definitely confirm that C. gigas belongs in the Chiasmolithus bidens group (bars divided by a median extinction line in XPL) rather than the Chiasmolithus consuetus group.
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Jeremy Young (UCL, UK)
Very good point. I followed Perch-Nielsen (1985) and Varol (1992) here who did place gigas in this group but I am not sure that Gartner (1970) included gigas in his consuetus group. I will ask Paul Bown to take a look at this.
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Jeremy Young (UCL, UK)
I have now transferred gigas to the bidens group. Gartner (1970) and Romein (1979) both place it in this group, on the basis of crossbar structure.
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