Discoaster hamatus


Classification: Coccolithophores -> Discoasterales -> Discoasteraceae -> Discoaster -> D. pentaradiatus group -> Discoaster hamatus
Sister taxa: D. pentaradiatus, D. prepentaradiatus, D. hamatus, D. bellus,

Daughter taxa: Variants (could also be distinguished informally) (blue => in age window 0-800Ma)
Discoaster bolivariae
4-rayed D. hamatus
Discoaster triuncinus
3-rayed D. hamatus

Taxonomy:

Citation: Discoaster hamatus Martini and Bramlette, 1963
Rank: Species
Notes & discussion: This species seems to have an identical structure to that of the 6-rayed species D. calcaris (q.v.). Typically only large specimens (>c.10 microns) have well developed offset proximal extensions, associated smaller specimens lack these and are better placed in D. bellus for biostratigraphic rigour. Both the D. calcaris and D. bellus morphotypes have longer stratigraphic ranges than true D. hamatus.
Browning et al. (2017)  record that the smaller specimens (<15µm) occur above and below NN9 so for stratigraphic rigour the large specimens need to be used. 

Distinguishing features: 5-rayed; ray tips with clockwise deflected (in distal view) proximal extensions.

Farinacci & Howe catalog pages: Discoaster hamatus + * , Eu-discoaster hamatus *


Morphology remarks: Symmetric 5-rayed discoaster; rays with clockwise deflected (in distal view) proximal extensions. The central area is small with a featureless distal surface and small proximal knob.

Size: Usually only large specimens, (>10 µm) show the characteritic raytip development

Search data:
TagsLITHS: nannolith-radiate, star-shaped, RIM: free-rays-long, tips extended proximally, tips oblique, PROCESS: boss, boss-proximal,
CSPH: not known, V-UNITS: all, R-UNITS: none, DETAILS: 1ou,
MetricsLith size: 10->25µm; Segments: 5->5;
Sources: size from OD & illustrated specs
The morphological data given here can be used on the advanced search page. See also these notes

See also: Discoaster calcaris - similar but with 6-rays and longer ranging;

Geological Range:
Notes: Defines Zone NN9
Last occurrence (top): at top of NN9 zone (100% up, 9.5Ma, in Tortonian stage). Data source: zonal marker (see e.g. Young 1998)
First occurrence (base): at base of NN9 zone (0% up, 10.6Ma, in Tortonian stage). Data source: zonal marker (see e.g. Young 1998)

Plot of occurrence data:

  • Histogram - Neptune occurrence data from DSDP and ODP proceedings. Pale shading <50 samples in time bin. Interpret with caution & read these notes
  • Note to users in China - the diagram may not plot unless you use a VPN since I use google services on the website. If this is a problem please contact me 谢谢.
  • Taxon plotted: Discoaster hamatus, synonyms included - Discoaster hamatus;
  • space-time plot :: Samples map :: Parent: D. pentaradiatus group

    References:

    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. gs

    Martini, E. & Bramlette, M. N. (1963). Calcareous nannoplankton from the experimental Mohole drilling. Journal of Paleontology. 37: 845-855. gs

    Perch-Nielsen, K. (1972). Remarks on Late Cretaceous to Pleistocene coccoliths from the North Atlantic. Initial Reports of the Deep Sea Drilling Project. 12: 1003-1069. gs

    Theodoridis, S. (1984). Calcareous nannofossil biostratigraphy of the Miocene and revision of the helicoliths and discoasters. Utrecht Micropaleontological Bulletin. 32: 1-271. gs

    Wei, W. (2003). Upper Miocene nannofossil bistratigraphy and taxonomy of Exxon core CH30-43-2 from the Gulf of Mexico. Journal of Nannoplankton Research. 25(1): 17-23. gs

    Young, J. R. (1998). Neogene. In, Bown, P. R. (ed.) Calcareous Nannofossil Biostratigraphy. British Micropalaeontological Society Publication Series. 225-265. gs

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    Discoaster hamatus compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 18-10-2019

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