Discoasterales


Classification: Coccolithophores -> Discoasterales
Sister taxa: advancedsearch.php, Isochrysidales, Coccolithales, Zygodiscales, Syracosphaerales, Coccolith families inc sed, Mesozoic Survivors, Holococcoliths, Braarudosphaerales, Discoasterales, Nannolith families inc sed, hidden,

Short diagnosis: Radially symmetrical nannoliths formed from one to several separate cycles of elements that radiate from a common centre or axis.


Daughter taxa (blue => in age window 0-300Ma) Granddaughter taxa
Discoidal discoasteralids formed of one, non-birefringent in plan view, cycle.

Conical or cylindrical discoasteralids consisting of 10-30 wedge-shaped, radially-arranged elements, in one to three superposed cycles.

Discoidal discoasteralids with several distinct cycles including at least one that is birefringent.

Conical discoasteralids with a concave base, consisting of a mass of elements radiating from a common origin.

Taxonomy:

Citation: Discoasterales Hay, 1977
Rank: Order
Notes & discussion: Hay (1977) described the Order Discoasterales as a broad taxonomic group that included most radial and stellate Mesozoic and Cenozoic nannoliths. It is used here as a narrower taxonomic concept that incorporates the type family, the Discoasteraceae, together with the other radially symmetrical Paleogene nannolith groups, the Heliolithaceae, Fasciculithaceae and Sphenolithaceae, which originated within four million years of one another and have common morphological features suggesting phylogenetic affinity (Bown 2010).
The term discoasteralids is used here as a concise term for nannoliths produced by members of the order Discoasterales.

Farinacci & Howe catalog pages: Discoasterales [no catalog entry yet]

Short diagnosis: Radially symmetrical nannoliths formed from one to several separate cycles of elements that radiate from a common centre or axis.


Morphology remarks: Includes disc-like (discoasters), stellate (discoasters), cylindrical (fasciculiths, helioliths and sphenoliths) and conical (fasciculiths and sphenoliths) morphologies, but all with rotational symmetry about a single axis. The top and bottom surfaces, relative to the axis of rotation are usually different and one surface is normally concave and is considered proximal. All members show complex crystal units with control of both a-axis and c-axis orientation. The structures are often chiral.

Evolution & Phylogeny: The earliest members of the Discoasterales appear in the Palaeocene and they show more similarities to heterococcoliths -see e.g. Aubry et al. 2011. They also share with radial symmetry and precise control of calcite crystallographic orientation and complex sculpting of individual calcite crystal units. They apparently lack however growth from a proto-coccolith ring and so presence of alternating V- and R-units. Phylogenetically it seems reasonable to infer that they evolved from heterococcoliths by modification of the biomineralisation process.

Search data:
TagsLITHS: nannolith-radiate,
CSPH: not known,
MetricsLith size: 0->0┬Ám;
Sources:
The morphological data given here can be used on the advanced search page. See also these notes

Geological Range:
Last occurrence (top): within Gelasian Stage (1.81-2.59Ma, top in Gelasian stage). Data source: Total of range of species in this database
First occurrence (base): within Danian Stage (61.61-66.04Ma, base in Danian stage). Data source: Total of range of species in this database

Plot of occurrence data:

References:

Bown, P.R., (2010). Calcareous nannofossils from the Paleocene/Eocene Thermal Maximum interval of southern Tanzania (TDP Site 14). Journal of Nannoplankton Research, 31: 11-38.

Hay, W.W., (1977). Calcareous nannofossils. In: Ramsay, A.T.S. (Editor), Oceanic Micropalaentology. Academic Press, London, pp. 1055-1200.

Perch-Nielsen, K., (1985). Cenozoic calcareous nannofossils. In: Bolli, H.M., Saunders, J.B. and Perch-Nielsen, K. (Editors), Plankton Stratigraphy. Cambridge University Press, Cambridge, pp. 427-555.

Young, J.R., (1998). Neogene. In: Bown, P.R. (Editor), Calcareous Nannofossil Biostratigraphy. British Micropalaeontological Society Publications Series. Chapman & Hall, London, pp. 225-265.


nannotaxlogo400px

Discoasterales compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 16-12-2017

Taxon Search:
Advanced Search

Go to Archive.is to create a permanent copy of this page - citation notes



Comments (0)

No comments yet. Be the first!

Add Comment

* Required information
1000
Captcha Image
Powered by Commentics