Nannotax3 - ntax_cenozoic - D. variabilis group Nannotax3 - ntax_cenozoic - D. variabilis group

D. variabilis group


Classification: ntax_cenozoic -> 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 (time control age-window is: 0-800Ma)Granddaughter taxa
Species with trifurcate ray-tips
Discoaster surculus
6-rayed with trifurcate ray-tips, central branch directed proximally
Discoaster toralus

Discoaster pseudovariabilis
Central branch of trifurcate tip notched

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

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

Discoaster loeblichii
Like D. variabilis but bifurcations asymmetric
Discoaster breviloeblichii
Discoaster pachyloeblichii

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

Taxonomy:

Citation: Discoaster variabilis group
taxonomic rank: species group

Distinguishing features:
Parent taxon (Discoaster): Radiate nannoliths with each ray formed of a discrete crystal-unit, with the c-axes perpendicular to the nannolith surface.
This taxon: 6-rayed discoasters with bifurcations

Farinacci & Howe catalog pages:


Morphology:

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:
Lith size: 3->22µm;
The morphological data given here can be used on the advanced search page. See also these notes

Geological Range:
Last occurrence (top): at top of NN16 zone (100% up, 2.5Ma, in Gelasian stage). Data source: Total of ranges of the species in this database
First occurrence (base): within NN5 zone (13.53-14.91Ma, base in Langhian stage). Data source: Total of ranges 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: 11-9-2024

Taxon Search:
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Short stable page link: https://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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