Discoaster hamatus
Classification: ntax_cenozoic -> Discoasterales -> Discoasteraceae -> Discoaster -> D. pentaradiatus group -> Discoaster hamatus
Sister taxa: D. pentaradiatus, D. prepentaradiatus, D. hamatus, D. bellus
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Taxonomy:
Citation: Discoaster hamatus Martini and Bramlette, 1963Rank: SpeciesTaxonomic 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: D. hamatus + * , E. hamatus *
Morphology: 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
See also: Discoaster calcaris - similar but with 6-rays and longer ranging;
Search data:
| Tags | LITHS: nannolith-radiate, star-shaped, CA: process, CROSS-POLARS: 1ou, V-prominent, |
| Metrics | Lith size: 10->25µm; Segments: 5->5;
Data source notes: size from OD & illustrated specs |
The morphological data given here can be used on the advanced search page. See also these notes
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:
- 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. Pale shading <50 samples in time bin. Interpret with caution & read these notes
- Taxon plotted: Discoaster hamatus, synonyms included - Discoaster hamatus;
- See also 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 V O
Martini, E. & Bramlette, M. N. (1963). Calcareous nannoplankton from the experimental Mohole drilling. Journal of Paleontology. 37(4): 845-855. gs
Perch-Nielsen, K. (1972b). Remarks on Late Cretaceous to Pleistocene coccoliths from the North Atlantic. Initial Reports of the Deep Sea Drilling Project. 12: 1003-1069. gs V O
Theodoridis, S. (1984). Calcareous nannofossil biostratigraphy of the Miocene and revision of the helicoliths and discoasters. Utrecht Micropaleontological Bulletin. 32: 1-271. gs V O
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 V O
Young, J. R. (1998). Neogene. In, Bown, P. R. (ed.) Calcareous Nannofossil Biostratigraphy. British Micropalaeontological Society Publication Series. 225-265. gs V O
