Discoaster bellus


Ancestry: Coccolithophores -> Discoasterales -> Discoasteraceae -> Discoaster -> D. pentaradiatus group -> Discoaster bellus
Sister taxa: D. pentaradiatus, D. prepentaradiatus, D. hamatus, D. bellus,

Short diagnosis: Symmetric 5-rayed species with simple ray tips


Taxonomy:

Citation: Discoaster bellus Bukry and Percival, 1971
Rank: Species
Notes & discussion: D. bellus is a name available for non-birefringent symmetrical pentaradial discoasters with simple ray ends, and small central areas. Such forms occur commonly in association with D. hamatus (q.v.), and arguably intergrade with them, but in order to preserve the biostratigraphic value of D. hamatus it is important to separate unambiguous D. hamatus specimens from these more non-descript froms. Also D. bellus type discoasters persist at low abundances after the LO of D. hamatus, and probably gives rise to D. quinqueramus. As noted in the comments, D. prepentaradiatus specimens can also intergrade with D. bellus especially when bifurcations are removed due to dissolution.

Farinacci & Howe catalog pages: Discoaster bellus *

Short diagnosis: Symmetric 5-rayed species with simple ray tips


Morphology remarks: Symmetric 5-rayed species with simple ray tips. Intergrades with D. hamatus, but distinguishing it is useful to avoid recording ambiguous specimens as D. hamatus.

Geological Range:
Notes: FO in NN8, before D. hamatus is discussed in Theodoridis (1984) 
Last occurrence (top): within NN11 zone (5.59-8.29Ma, top in Messinian stage). Data source: Young 1998
First occurrence (base): within NN8 zone (10.55-10.89Ma, base in Tortonian stage). Data source: Young 1998

Plot of occurrence data:

References:

Bukry, D. & Percival, S.F., (1971). New Tertiary calcareous nannofossils. Tulane Studies in Geology and Paleontology, 8: 123-146.

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


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

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Comments (3)

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Aaron Avery (FSU, US)
On second thought Mike, you are right. I have been looking through the section again and noticed some very small 5 rayed forms that I could only describe as thin prepentaradiatus.
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Jeremy Young (UCL, UK)
good points - I have had samples where this was a very real problem.
I have now edited the text to note this.
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Aaron Avery (FSU, US)
I would argue that bellus is quite useful. I am working with material from the pacific where there is a clear difference between D. bellus and D. prepentaradiatus. In otherwords, the material is preserved well enough that D. prepentaradiatus and D. bellus appear together and make for useufl zonal constraint within certain assemblages. In my experience prepentaradiatus is much more robust. The argument about D. hamatus may be true, but it wouldn't be the first time an arbitrary distinction based on size was useful. I would also argue that bellus is closer to a non concavo-convex version of D. quinqueramus and the original description of simple ray tips is useful in distinguishing larger forms from hamatus.
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Mike Styzen (Noble Energy, US)
Just a junk box? I've always regarded this species as sort of a place to stash poorly preserved 5 rayed symmetrical discoasters which may really be several other things. Is there really an advantage to using \bellus"rather than something like \""Discoaster 5 ray\"""""
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Jeremy Young (NHM, UK)
fair question, I have always been in two minds on this, on the one hand I tend to agree that these are probably mostly small and/or poorly preserved D. hamatus specimens, on the other hand the count category \symmetric 5-rayed discoaster without bifurcations"is complex and D. bellus is a convenient name. As with many of these species a detailed study of samples with well preserved assemblages is probably what is needed - maybe a good student project?"""
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Mike Styzen (Noble Energy, US)
Not just D. hamatus: I think sometimes some poorly preserved/broken D. prepentaradiatus get stuck in this taxon as well.
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