|Daughter taxa: (blue => in age window 0-800Ma)||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.
The term discoasteralids is used here as a concise term for nannoliths produced by members of the order Discoasterales.
Distinguishing features: Radially symmetrical nannoliths formed from one to several separate cycles of elements that radiate from a common centre or axis.
Farinacci & Howe catalog pages: Discoasterales [no catalog entry yet]
Morphology: 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.
Phylogenetic relations: 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.
|Metrics||Lith size: 0->0µm;|
Last occurrence (top): near top of Gelasian Stage (85% up, 1.9Ma, in Gelasian stage). Data source: Total of range of species in this database
First occurrence (base): in upper part of Danian Stage (69% up, 63Ma, in Danian stage). Data source: Total of range of species in this database
Plot of occurrence data:
Hay, W. W. (1977). Calcareous nannofossils. In, Ramsay, A. T. S. (ed.) Oceanic Micropalaentology. Academic Press, London 1055-1200. gs 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
Hay, W. W. (1977). Calcareous nannofossils. In, Ramsay, A. T. S. (ed.) Oceanic Micropalaentology. Academic Press, London 1055-1200. gs
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
Short stable page link: http://mikrotax.org/Nannotax3/index.php?id=517 Go to Archive.is to create a permanent copy of this page - citation notes