Discoaster pentaradiatus
Classification: Coccolithophores -> Discoasterales -> Discoasteraceae -> Discoaster -> D. pentaradiatus group -> Discoaster pentaradiatus
Sister taxa: D. pentaradiatus, D. prepentaradiatus, D. hamatus, D. bellus,
Distinguishing features: Ray tips with acute bifurcations; strongly concavo-convex; birefringent
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Taxonomy:
Citation: Discoaster pentaradiatus Tan, 1927Rank: SpeciesVariants:
- Discoaster quadramus Bukry, 1973 - four rayed variant with the rays arranged in a flattened cross. Such specimens only occur very sporadically and they probably are malformed D. pentaradiatus specimens
- Discoaster ono Styzen, 1994 - very short non-bifurcate rays, probably a preservational artefact
Synonyms:
- Discoaster tridenus Kamptner, 1967 etched form, lacking bifurcations.
- Discoaster stradneri Cati & Borsetti 1970 - etched form, lacking bifurcations (invalid, homonym)
- Discoaster anconitanus Borsetti and Cati, 1972 - etched form, lacking bifurcations (replacement name for D. stradneri)
- Discoaster misconceptus (Theodoridis, 1984) Muza and Wise, in Muza et al., 1987 [Eudiscoaster] - alternative name proposed for nomenclatural reasons (see notes on species name).
Notes & discussion: Theodoridis (1984), argued that use of the name D. pentaradiatus for this species was based on a misconception of Tan's type specimen, and of Bramlette & Riedel's emended diagnosis. He proposed the alternative name E. misconceptus. This interpretation has not however been widely followed, and if an alternative name to D. pentaradiatus was used D. tridenus has priority over D. misconceptus.
Farinacci & Howe catalog pages: Discoaster anconitanus + * Discoaster ono * Discoaster pentaradiatus + * Discoaster quadramus * Discoaster stradneri Cati and Borsetti [no catalog entry yet]Discoaster tridenus + * Eu-discoaster misconceptus *
Distinguishing features: Ray tips with acute bifurcations; strongly concavo-convex; birefringent
Morphology remarks: 5-rayed discoaster (with rare 3 and 4 rayed variants); ray tips with acute bifurcations. Strongly concavo-convex and birefringent (each ray is a separate crystal-unit, with c-axes inclined slightly from vertical toward radial). The central area is small, but distinct. It often has scalloped depressions and/or sutural ridges on the distal side, also a stellate proximal knob.
This is a very distinctive species; both the acutely angled bifurcations and the birefringence, with each ray showing slightly different optical orientation are diagnostic of the species. With dissolution the bifurcations can be removed and such forms have been described as separate species (see synonyms), however the birefringence allows definitive identification of such specimens.
Search data:
| Tags | LITHS: nannolith-radiate, star-shaped, RIM: tips-bifurcate, free-rays-long, PROCESS: boss, boss-proximal,
CSPH: not known, V-UNITS: all, R-UNITS: none, |
| Metrics | Lith size: 8->20µm; Segments: 5->5;
Sources: size from illustrated specs |
The morphological data given here can be used on the advanced search page. See also these notes
Geological Range:
Notes: Often very abundant, but highly susceptible to dissolution.
Raffi et al. (2006) record the FAD within NN10, at the base of chron C4An, and nearly coincident with the onset of th small Reticulofenestra event. However, there are definite records of the species below this, into NN9 (e.g. Browning et al. 2017), so this is probably better treated as a lowest common occurrence horizon, or possibly as a crossover with D. prepentaradiatus.
Last occurrence (top): at top of NN17 zone (100% up, 2.4Ma, in Gelasian stage). Data source: zonal marker (see e.g. Young 1998)
First occurrence (base): at base of Chron C4An sub-Magnetochron (0% up, 9.1Ma, in Tortonian stage). Data source: Raffi et al. 2006 (but this is LCO, rare occurrences persist to upper NN9 - e.g. Browning et al. (2017)
Plot of occurrence data:
- Range-bar - range as quoted above, pink interval top occurs in, green interval base occurs in.
- Triangles indicate an event for which a precise placement has been suggested
- Histogram - Neptune occurrence data from DSDP and ODP proceedings. Interpret with caution & read these notes
- Taxon plotted: Discoaster pentaradiatus, synonyms included - Discoaster brouweri tridens; Discoaster misconceptus; Discoaster ono; Discoaster pentaradiatus; Discoaster pentaradiatus (fragments); Discoaster pentaradiatus (grainy); Discoaster quadramus; Discoaster tridenus; space-time plot ::
Samples map :: Parent: D. pentaradiatus group
References:Borsetti, A.M. & Cati, F., (1972). Il Nannoplancton calcareo vivente nel Tirreno Centro-meridionale. Giornale di Geologia, 38(II): 395-452.
Browning, E.; Bergen, J.A.; Blair, S.A.; Boesiger, T.M. & de Kaenel, E., (2017). Late Miocene to Late Pliocene taxonomy and stratigraphy of the genus Discoaster in the circum North Atlantic Basin: Gulf of Mexico and ODP Leg 154. Journal of Nannoplankton Research, 37(2-3): 189-214.
Bukry, D., (1973). Phytoplankton stratigraphy, Deep Sea Drilling Project Leg 20, Western Pacific Ocean. Initial Reports of the Deep Sea Drilling Project, 20: 307-317.
Cati, F. & Borsetti, A.M., (1970). I discoasteridi del Miocene delle Marche. Giornale di Geologia, 36(2): 617-652.
Kamptner, E., (1967). Kalkflagellaten - Skelettreste aus Tiefseeschlamm des Südatlantischen Ozeans. Annalen des Naturhistorischen Museums in Wien, 71: 117-198.
Muza, J.P.; Wise, S.W. & Covington, J.M., (1987). Neogene calcareous nannofossils from Deep Sea Drilling Project Site 603, lower continental rise, western North Atlantic: biostratigraphy and correlation with magnetic and seismic stratigraphy. Initial Reports of the Deep Sea Drilling Project, 93: 593-616.
Raffi, I.; Backman, J.; Fornaciari, E.; Palike, H.; Rio, D.; Lourens, L.J. & Hilgen, F.J., (2006). A review of calcareous nannofossil astrobiochronology encompassing the past 25 million years. Quaternary Science Reviews, 25: 3113-3137.
Tan, S.H., (1927). Discoasteridae incertae sedis. Proceedings of the Koninklijke Nederlandse Akademie van Wetenschappen, Sect Sci, 30: 411-419.
Theodoridis, S., (1984). Calcareous nannofossil biostratigraphy of the Miocene and revision of the helicoliths and discoasters. Utrecht Micropaleontological Bulletin, 32: 1-271.
Young, J.R., (1998). Neogene. In: Bown, P.R. (Editor), Calcareous Nannofossil Biostratigraphy. British Micropalaeontological Society Publications Series. Chapman & Hall, London, pp. 225-265.
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