R. umbilicus group


Classification: Coccolithophores -> Isochrysidales -> Noelaerhabdaceae -> Reticulofenestra -> R. umbilicus group
Sister taxa: C. floridanus group, R. bisecta group, R. lockeri group, R. parvula group, R. pseudoumbilicus group, R. reticulata group, R. umbilicus group, R. sp.,

Daughter taxa: (blue => in age window 0-800Ma)
elliptical species
Very large (>14 µm) elliptical reticulofenestrids, with delicate net
Small to very large (3-14 µm), elliptical reticulofenestrids with open central area spanned by net
Large to very large (~>9µm), broadly elliptical reticulofenestrids with broad tube and narrow central area that can be distinctly quadrate or lens-shaped.
Medium sized, elliptical reticulofenestrid with broad central area.
Cocoliths small to medium sized (3-7µm) with central area nearly closed by inner tube cycle
Normally elliptical reticulofenestrid with relatively wide central area and a net that is faintly visible or imperceptible.
sub-circular species
Medium-sized, subcircular Reticulofenestra with a thin tube and a medium-sized central opening with quadrate outline.
Very large (>12 microns), sub-circular Reticulofenestra with a medium-sized central opening with quadrate outline.
Medium to large subcircular Reticulofenestra with wide central area (= to width of shields) and no visible net or grill in light microscope.
broad central area & flaring collar
Medium sized Reticulofenestra with inner tube extended as flaring collar
Large elliptical Reticulofenestra with narrow rim, flaring-collar, and very wide central area filled with a finely perforate plate divided by a median suture

Taxonomy:

Citation: R. umbilicu group
Rank: species group
Notes & discussion: There is a high degree of variability within this group, which has been informally divided using simple coccolith length categories (see, e.g., Young, 1990). Forms with broadly elliptical to subcircular outlines and/or narrower central areas can be difficult to distinguish from species of the Cyclicargolithus group.

Distinguishing features: Paleogene elliptical reticulofenestrids with open central area (spanned by delicate proximal net, not visible in lm)

Farinacci & Howe catalog pages:

Search data:
Tags
CSPH: spherical, V-UNITS: none, R-UNITS: all, c-str, distal shield, prox shield, tube, DETAILS: isogyres kinked, isogyres oblique,
MetricsLith size: 3->20µm;
Sources:
The morphological data given here can be used on the advanced search page. See also these notes

Geological Range:
Notes: Common, middle Eocene-lower Oligocene. In the Neogene similar species occur but are conventionally assigned to different species, placed here in the R. pseudoumilicus group.
Last occurrence (top): at top of Chattian Stage (100% up, 23Ma, in Chattian stage). Data source: Total of range of species in this database
First occurrence (base): in upper part of Ypresian Stage (67% up, 50.5Ma, in Ypresian stage). Data source: Total of range of species in this database

Plot of occurrence data:

References:

Perch-Nielsen, K. (1985a). Cenozoic calcareous nannofossils. In, Bolli, H. M. , Saunders, J. B. & Perch-Nielsen, K. (eds) Plankton Stratigraphy. Cambridge University Press, Cambridge 427-555. gs :: ::


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R. umbilicus group compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 30-5-2020

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Short stable page link: http://mikrotax.org/Nannotax3/index.php?id=1151 Go to Archive.is to create a permanent copy of this page - citation notes



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