Nannotax3 - ntax_cenozoic - Discoaster bellus Nannotax3 - ntax_cenozoic - Discoaster bellus

Discoaster bellus


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

Variants (could also be distinguished informally) (time control age-window is: 0-800Ma)
Discoaster astellaris
Like D. bellus but asymmetric
Discoaster gemmulatus
Like D. bellus but with weak central knob

Taxonomy:

Citation: Discoaster bellus Bukry&Percival, 1971
taxonomic rank: Species
Taxonomic 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.

Distinguishing features:
Parent taxon (D. pentaradiatus group): Symmetric 5-rayed, late Neogene, discoasters without large proximal boss
This taxon: Symmetric 5-rayed species with simple ray tips

Farinacci & Howe catalog pages: D. bellus *


Morphology:

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.

Search data:
LITHS: nannolith-radiate, star-shaped, CA: process, CROSS-POLARS: 1ou, V-prominent,
Lith size: 7->14µm; Segments: 5->5;
Data source notes: size from OD & illustrated specs
The morphological data given here can be used on the advanced search page. See also these notes

Geological Range:
Notes: FO in NN8, before D. hamatus is discussed in Theodoridis (1984). Blair et al. (2017) document it in more detail and also LAD in lower part of NN11.  
Last occurrence (top): in lower part of NN11 zone (20% up, 7.8Ma, in Tortonian stage). Data source: Blair et al. 2017
First occurrence (base): within NN8 zone (10.55-10.89Ma, base in Tortonian stage). Data source: Young 1998; Blair et al. 2017

Plot of occurrence data:

References:

Blair, S. A., Bergen, J. A., de Kaenel, E., Browning, E. & Boesiger, T. M. (2017). Upper Miocene-Lower Pliocene taxonomy and stratigraphy in the circum North Atlantic Basin: radiation and extinction of Amauroliths, Ceratoliths and the D. quinqueramus lineage. Journal of Nannoplankton Research. 37(2-3): 113-144. gs O

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

de Kaenel, E. & Villa, G. (1996). Oligocene-Miocene calcareous nannofossil biostratigraphy and paleoeecology from the Iberian Abyssal Plain. Proceedings of the Ocean Drilling Program, Scientific Results. 149: 79-145. gs O

Theodoridis, S. (1984). Calcareous nannofossil biostratigraphy of the Miocene and revision of the helicoliths and discoasters. Utrecht Micropaleontological Bulletin. 32: 1-271. gs O

Young, J. R. (1998). Neogene. In, Bown, P. R. (ed.) Calcareous Nannofossil Biostratigraphy. British Micropalaeontological Society Publication Series . 225-265. gs

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Discoaster bellus compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 11-9-2024

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Short stable page link: https://mikrotax.org/Nannotax3/index.php?id=450 Go to Archive.is to create a permanent copy of this page - citation notes
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Comments (6)

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Aaron Avery(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(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(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(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(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(US)
Not just D. hamatus: I think sometimes some poorly preserved/broken D. prepentaradiatus get stuck in this taxon as well.