Orastrum robinsonii


Classification: Mesozoic -> Holococcoliths -> Common genera -> Orastrum -> Orastrum robinsonii
Sister taxa: O. asarotum, O. campanensis, O. porosuturalis, O. perspicuum, O. robinsonii, O. colligatum, O. sp.,

Distinguishing features: Single low birefringence central plate with indistinct cross-like central structure surrounded by multiple perforations. Medium sized (5-6 µm)


Taxonomy:

Citation: Orastrum robinsonii Lees, 2007
Rank: Species

Farinacci & Howe catalog pages: Orastrum robinsonii *

Distinguishing features: Single low birefringence central plate with indistinct cross-like central structure surrounded by multiple perforations. Medium sized (5-6 µm)


Morphology remarks: "A medium-sized species of Orastrum that in XPL has a bright rim and dark central plate, bearing a usually barely-discernable x-shaped structure. At 0 ̊ in XPL, the extinction lines are aligned with the polarising directions, appearing darker on the rim and barely discernable on the plate. On rotation, these become v-shaped on the rim, occupying the ends of the lith, but bend where they move onto the plate, where again they are barely discernable. In PC, the plate appears to be multiperforate (Pl.10, fig.3). Differentiation: The size and relatively wide rim and central area are distinctive. The x-shaped central structure distinguishes it from other species of the genus." [Lees 2007]

Size: Holotype dimensions: L = 6.16μm, 4.84μm

Geological Range:
Last occurrence (top): within Late Cenomanian Substage (93.90-95.47Ma, top in Cenomanian stage). Data source: Lees 2007 (original description)
First occurrence (base): within Early Cenomanian Substage (96.24-100.50Ma, base in Cenomanian 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: Orastrum

    References:

    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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    Orastrum robinsonii compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 16-10-2019

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    Short stable page link: http://mikrotax.org/Nannotax3/index.php?id=10827 Go to Archive.is to create a permanent copy of this page - citation notes



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