Jimenezberrocosoia bosunensis


Classification: Mesozoic -> Podorhabdales -> Biscutaceae -> Jimenezberrocosoia -> Jimenezberrocosoia bosunensis
Sister taxa: J. birchiae, J. bosunensis,

Distinguishing features: Medium sized (4-6µm) with narrow central area and birefringent cross. Short-axis crossbar brighter than long-axis crossbar.


Taxonomy:

Citation: Jimenezberrocosoia bosunensis (Jeremiah, 2001) Lees & Bown 2016
Rank: Species
Basionym: Crucibiscutum bosunensis Jeremiah, 2001
Notes & discussion: Lees (2007) questionably identified LM images of this form as Crucibiscu­tum salebrosum, which, based on Black’s holotype (SEM of promixal view), has a central cross that almost fills the central-area and comprises four almost equidimensional bars. Unfortunately, Black (1971) did not provide any LM images and so later reports of C. salebrosum have depended on LM interpretations of that holotype; however, these seem to show that the central cross is entirely birefringent (e.g. Bown et al., 1998, pl.10, g.25). Whilst Jeremiah (2001) admitted that he was essentially using stratigraphic non-contiguity to distinguish between his new C. bosunensis and C. salebrosum, his LM holotype actually shows a distinctly longer, dark axial bar, with the shorter short-axis bars being highly birefringent when rotated. So, the Lees (2007) images actually conform to bosunensis, in terms of overall XPL view, size and central-area proportions. 
On closer inspection, our LM images show that our forms have Jimenezberrocosoia-style rim-slits, especially visible when viewed in PC (Pl.1, g.7) or PPL (Pl.1, gs 12, 13). We contend that our LM images of bosunensis conform to the SEM images in Pl.1, gs 5 and 10, and that these are simply well-preserved forms of bosunensis. Thus, we have placed bosunensis into Jimenezberro­cosoia. [Lees & Bown 2016]

Farinacci & Howe catalog pages: Crucibiscutum bosunensis * , Jimenezberrocosoia bosunensis * ,

Distinguishing features: Medium sized (4-6µm) with narrow central area and birefringent cross. Short-axis crossbar brighter than long-axis crossbar.


Morphology remarks: Very similar to C. salebrosum, but younger, discrete stratigraphic distribution.

Broadly elliptical, small to medium-sized (~4–6μm long) Jimenez­berrocosoia coccoliths; rim dark in XPL, with bright inner cycle; relatively short slits between elements of distal shield particularly visible in PPL (may not be visible in less well-preserved specimens); moderately wide, open, elongate-elliptical central-area (approximately equal to width of rim) spanned by axial cross-bars, long-axis bar being subrhomboidal in centre, but thinning into straight ends that attach to inner tube-cycle, surrounded by a single set of concentric bars (Pl.1, fig.10; note that concentric bars visible in SEM images are not particularly visible in any of our LM images); short, straight short-axis bars appear bright at 45 ̊ rotation, whilst long-axis bar goes into extinction. Proximal view shows again rim composed of elongated, widely-spaced elements and central cross structure attached to inner tube-cycle, proximally (Pl.1, fig.5). [Lees & Bown 2016]

Differentiation: This species is distinct from J. birchiae because the rim slits in bosunensis appear to be relatively shorter, the central-area is relatively wider, the central cross is constructed of different-shaped bars, and birchiae bears a small spine; bosunensis is also larger (~4-6 µm vs. <=3 µm). [Lees & Bown 2016]

See also: Crucibiscutum salebrosum ;

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 Late Aptian Substage (112.95-122.98Ma, base in Aptian stage). Data source: Jeremiah 2001

Plot of occurrence data:

  • Histogram - Neptune occurrence data from DSDP and ODP proceedings. Pale shading <50 samples in time bin. Interpret with caution & read these notes
  • Note to users in China - the diagram may not plot unless you use a VPN since I use google services on the website. If this is a problem please contact me 谢谢.
  • Taxon plotted: Jimenezberrocosoia bosunensis, synonyms included - Crucibiscutum bosunensis; space-time plot :: Samples map :: Parent: Jimenezberrocosoia

    References:

    Jeremiah, J. (2001). A Lower Cretaceous nannofossil zonation for the North Sea Basin. Journal of Micropalaeontology. 20: 45-80. gs

    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


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    Jimenezberrocosoia bosunensis compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 20-7-2019

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    Short stable page link: http://mikrotax.org/Nannotax3/index.php?id=10537 Go to Archive.is to create a permanent copy of this page - citation notes



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