Nannoconus nicholasii


Classification: Mesozoic -> Braarudosphaerales -> Nannoconaceae -> Nannoconus -> Nannoconus - atypical -> Nannoconus nicholasii
Sister taxa: N. funiculus, N. ligius, N. magnadiscus, N. nicholasii, N. pseudoseptentrionalis, N. sabinae,

Distinguishing features: Short, parallel-sided Nannoconus, formed of triangular plates with a median depression, bordered by ridges, creating a shallow ‘w’- shaped margin.


Taxonomy:

Citation: Nannoconus nicholasii (Lees, 2007) Lees & Bown 2016
Rank: Species
Basionym: Micrantholithus nicholasii Lees, 2007
Notes & discussion:

 

Farinacci & Howe catalog pages: Micrantholithus nicholasii + *

Distinguishing features: Short, parallel-sided Nannoconus, formed of triangular plates with a median depression, bordered by ridges, creating a shallow ‘w’- shaped margin.


Morphology remarks: Composed of distinctively-shaped segments with a ridge-bordered central depression and crenulated outer edge that has not been seen in any other species. [Lees 2007]

Since the original description of this species, based on individual elements seen in the LM (Pl.4, g.6), we have found these elements in associations in the SEM that allow us to determine that these are nannoconid, not micrantholithid, elements (Pl.4, g.2). Although our description of N. funiculus allows for at least part of its structure to be made of a similar type of element, those Lees (2007) originally described belong to a nannoconid found more commonly in the LM in the original samples of TDP Site 15. This medium-sized species is a relatively short and wide, parallel-sided nannoconid, with a narrow canal. It is composed of subtriangular elements with one scalloped edge, resulting in a point in the middle of that edge, giving the appearance of a trilobed fan (Pl. 4, g. 6). Each element has two sutures, extending from the incised parts of the scalloped edge and meeting at the opposing point. The elements also exhibit striae on their faces (Pl.4, gs 2, 3). These elements are arranged subhorizontally in this nannoconid, with the scalloped edge facing outwards (Pl.4, g.1). The elements imbricate, with one- third of one element covering one-third of the previous element, such that the lobes of the scalloped edges are always in alignment, giving a vertically ribbed effect in side view and an angular-petaliform end view (Pl.4, gs 4, 5). In the LM, these are most commonly seen in end view, typified by a distinctive outline and relatively low birefringence for a nannoconid. [Lees & Bown 2016]


Size: L = 5.2μm, W = 7.0μm [Lees & Bown 2016]

Search data:
TagsLITHS: nannolith-radiate, circular, star-shaped, cylindrical, triangular, hollow, CA: vacant, T-UNITS: T-prominent,
MetricsLith size: 5->8µm;
Sources: illustrated specimens
The morphological data given here can be used on the advanced search page. See also these notes

Geological Range:
Last occurrence (top): within Coniacian Stage (86.26-89.77Ma, top in Coniacian stage). Data source: Lees & Bown 2016
First occurrence (base): within Early Turonian Substage (92.90-93.90Ma, base in Turonian stage). Data source: Lees 2007 (original description)

Plot of occurrence data:

  • (NB There is no histogram as there are no occurrence records for the taxon in the Neptune database) Parent: Nannoconus - atypical

    References:

    Lees, J. A. & Bown, P. R. (2016). New and intriguing calcareous nannofossils from the Turonian (Upper Cretaceous) of Tanzania. Journal of Nannoplankton Research. 36(1): 83-95. gs

    Lees, J. A. (2007). New and rarely reported calcareous nannofossils from the Late Cretaceous of coastal Tanzania: outcrop samples and Tanzania Drilling Project Sites 5, 9 and 15. Journal of Nannoplankton Research. 29(1): 39-65. gs


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    Nannoconus nicholasii compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 9-4-2020

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    Short stable page link: http://mikrotax.org/Nannotax3/index.php?id=10763 Go to Archive.is to create a permanent copy of this page - citation notes



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