D. variabilis group


Classification: Coccolithophores -> Discoasterales -> Discoasteraceae -> Discoaster -> D. variabilis group
Sister taxa: D. brouweri group, D. pentaradiatus group, D. quinqueramus group, D. variabilis group, D. exilis group, D. musicus group, D. deflandrei group, D. nodifer group, D. lodoensis group, D. multiradiatus group, D. araneus group, D. sp.,

Daughter taxa: (blue => in age window 0-800Ma) Granddaughter taxa
Species with trifurcate ray-tips
6-rayed with trifurcate ray-tips, central branch directed proximally

=D. surculus variant with weakly developed bifurcations, central area broad with thin inter-ray areas, giving "webbing" appearance

Central branch of trifurcate tip notched

Like D. exilis but with knob or tongue between the bifurcations

D. variabilis and variants
6-rayed discoaster with well-developed bifurcate tips; slightly concavo-convex and proximal and distal sides well-differentiated.

Like D. variabilis but with "flaps" between the bifurcations

Like D. variabilis but with very broad bifurcations and >15 µm in diameter

Like D. variabilis but with very broad bifurcations and <15 µm in diameter

Like D. variabilis but with narrow bifurcations

Like D. variabilis but bifurcations asymmetric

Like D. variabilis but bifurcations narrow and tapering, central area broad

Taxonomy:

Citation: Discoaster variabilis group
Rank: species group

Distinguishing features: 6-rayed discoasters with bifurcations

Farinacci & Howe catalog pages:


Morphology remarks: 6-rayed discoasters with bifurcations. This is the predominant group of Early and Middle Miocene discoasters. N.B. Asymmetric 5-rayed specimens of all these species occasionally occur, and, especially in the Early Miocene, 7-rayed forms.
The dominant species are succesively D. deflandrei (NN1-5), D. exilis (NN6-10), and D. variabilis + D. surculus (NN10-16) but they intergrade and are of limited proven biostratigraphic value, except for the LOs of D. variabilis and D. surculus.
The other species in the group intergrade with the dominant Discoaster species but represent distinctive end-member morphologies which are of biostratigraphic value, e.g.: D. petaliformis D. musicus, D. kugleri, D. bollii. NB Discussion of species concepts in this group is very welcome.
Mike Styzen - In the GOM D. sanmiguelensis is used as a marker and is distinguished as being somewhat smaller than D. musicus with shorter rays. One might argue that what we are using is just a specific morphotype of D. musicus, but in any case its a distinction that has stratigraphic function. Richard Howe was kind enough to let me use an image of our D. sanmiguelensis concept.

Search data:
TagsLITHS: nannolith-radiate, star-shaped,
CSPH: not known, V-UNITS: all, R-UNITS: none, DETAILS: 1ou,
MetricsLith size: 3->22µm;
Sources:
The morphological data given here can be used on the advanced search page. See also these notes

Geological Range:
Last occurrence (top): near base of Gelasian Stage (13% up, 2.5Ma, in Gelasian stage). Data source: Total of range of species in this database
First occurrence (base): in mid part of Langhian Stage (49% up, 14.9Ma, in Langhian stage). Data source: Total of range of species in this database

Plot of occurrence data:

References:


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D. variabilis group compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 13-11-2019

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Short stable page link: http://mikrotax.org/Nannotax3/index.php?id=425 Go to Archive.is to create a permanent copy of this page - citation notes



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