Sphenolithus pseudoradians


Ancestry: Coccolithophores -> Discoasterales -> Sphenolithaceae -> Sphenolithus -> S. radians group -> Sphenolithus pseudoradians
Sister taxa: S. arthurii, S. orphanknollensis, S. pseudoradians, S. radians, S. richteri, S. runus, S. spiniger,

Short diagnosis: Medium to large sphenolith with a tall compound spine. Distinguished from Sphenolithus radians by its larger size, more irregular outline and apical cycles that extend laterally beyond the base of the apical spine.


Taxonomy:

Citation: Sphenolithus pseudoradians Bramlette & Wilcoxon, 1967
Rank: Species
Notes & discussion: The first occurrence of S. pseudoradians marks the base of zone NP20 (Martini 1971), however the application of this event is problematic due to the difficulties in reliably distinguishing between S. radians and S. pseudoradians.

Farinacci & Howe catalog pages: Sphenolithus pseudoradians *

Short diagnosis: Medium to large sphenolith with a tall compound spine. Distinguished from Sphenolithus radians by its larger size, more irregular outline and apical cycles that extend laterally beyond the base of the apical spine.

Geological Range:
Notes: The base of S. pseudoradians was used as the zonal marker for the NP19/20 boundary but the species ranges much lower so this typically the zones are combined - as NP19/20 - (see Perch-Nielsen 1985).
Last occurrence (top): within NP24 zone (26.84-29.62Ma, top in Chattian stage). Data source: Perch-Nielsen 1985b
First occurrence (base): within NP15 zone (42.87-46.29Ma, base in Lutetian stage). Data source: Perch-Nielsen 1985

Plot of occurrence data:

References:

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.

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.


Nannotax3 - Coccolithophores - Sphenolithus pseudoradians by: Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 29-6-2017

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Simon Cole (UK)
Like my comment just now about H. compacta; again, I don't believe this species goes to the top of NP24 (and therefore not to 26.84Ma). P-N, 1985 dashes to NP24 so I don't think we should be referencing that as the source of the date for the LO of this species without a question-mark at least.
Because I have found the same issue for H. compacta and S. pseudoradians in the last few minutes, it makes me wonder whether there are many other 'mis-referenced' ranges within Nannotax and could this be a wider issue? Due to the success of Nannotax (I for one love it!), I know many people are using it as the 'be all and end all' for ranges of taxa (amongst other things) so we need to ensure that either the ranges are correct and that we reference the ranges accurately. I think it is ok to quote say 'NP24' if the species tops within that zone but having an absolute age next to it signifying the species goes to the top of that zone, may not always be correct.
Cheers.
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Jeremy Young (UCL, UK)
Hi Simon
Yes it is a good point - the age ranges in nannotax are not heavily researched data from the literature and they are stored in whatever units the original sources used - eg NN zones or Cretaceous stages - the conversion of these to Ma ages is just for convenience but I think people are bit liable to misinterpret them.
Jeremy
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