Sphenolithus belemnos

Ancestry: Coccolithophores -> Discoasterales -> Sphenolithaceae -> Sphenolithus -> S. heteromorphus group -> Sphenolithus belemnos
Sister taxa: S. belemnos, S. calyculus, S. delphix, S. disbelemnos, S. milanetti, S. pospichalii, S. pseudoheteromorphus, S. heteromorphus,

Short diagnosis: Dart-shaped, apical spine well-developed. Lateral elements much smaller than proximal elements.


Citation: Sphenolithus belemnos Bramlette and Wilcoxon, 1967
Rank: Species
Notes & discussion: This species has a well developed monolithic spine with straight extinction. It can be distinguished from other species of this type by the nature of its base. This has a tall well-developed proximal cycle, but only diminutive lateral elements, overall the base is distinctly elongate, and merges smoothly into the spine.

Farinacci & Howe catalog pages: Sphenolithus belemnos *

Short diagnosis: Dart-shaped, apical spine well-developed. Lateral elements much smaller than proximal elements.

Size: : Length 4-8 microns, width 2-4 microns.

Geological Range:
Notes: Zone NN3 was origiinally defined by Martini (1971) as going from LAD T. carinatus to LAd S. belemnos<,i> but in pracice most workers use FAD S. belemnos to LAD S. belemnos. Where the orignal defintion is followed NN3 is shown as haiving a very short duration.
Last occurrence (top): in lower part of chron C5Dr.2r sub-Magnetochron (20% up, 18Ma, in Burdigalian stage). Data source: Raffi et al. (2006), fig 5
First occurrence (base): in upper part of chron C6N sub-Magnetochron (70% up, 19Ma, in Burdigalian stage). Data source: Raffi et al. 2006, fig. 5

Plot of occurrence data:


Bramlette, M.N. & Wilcoxon, J.A., (1967). Middle Tertiary calcareous nannoplankton of the Cipero section, Trinidad, W.I. Tulane Studies in Geology and Paleontology, 5: 93-131.

Young, J.R., (1998). Neogene. In: Bown, P.R. (Editor), Calcareous Nannofossil Biostratigraphy. British Micropalaeontological Society Publications Series. Chapman & Hall, London, pp. 225-265.

Nannotax3 - Coccolithophores - Sphenolithus belemnos by: Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 28-4-2017

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Mike Styzen (Noble Energy, US)
If you look at the photos with the original description, you will see that what is illustrated here is clearly not the same bug. In the original photos the basal cycle, immediately below the apical spine is distinctly asymmetric with one of the two elements being much smaller. In the same view (at 45 degrees to the nichols) the column shows a single dark line with 2 visible elements not the 3 seen in these photos. I've just been through this section in excruciating detail. The forms illustrated here range considerably higher than those that resemble the original illustrations. You can see the original photos in either P.N. 1985 or in the Aubry Handbook and you'll see what I mean.
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