INA16 Athens - September 2017

Discoaster pentaradiatus


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

Short diagnosis: Ray tips with acute bifurcations; strongly concavo-convex; birefringent


Taxonomy:

Citation: Discoaster pentaradiatus Tan, 1927
Rank: Species
Variants:
Synonyms:
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 + * Discoaster tridenus + * Eu-discoaster misconceptus *

Short diagnosis: 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 uniquely diagnostic of the species. With dissolution the bifurcations can be removed and such forms have been described as separate species (see synonyms below), however the birefringence allows definitive identification of such specimens.

Geological Range:
Notes: More specifically the range starts at NN10b. Often very abundant, but highly susceptible to dissolution.
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

Plot of occurrence data:

References:

Borsetti, A.M. & Cati, F., (1972). Il Nannoplancton calcareo vivente nel Tirreno Centro-meridionale. Giornale di Geologia, 38(II): 395-452.

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.

Nannotax3 - Coccolithophores - Discoaster pentaradiatus by: Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 29-6-2017

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Comments (1)

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J Kell (Lincoln Nebraska, US)
I don't believe either of these are D. pentaradiatus.

[NB This comment refers to a pair of specimens illustrated by Young 1998 pl8 fig21 - this is the black and white set of four images in the collection of images on this page; JRY March 2014]
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Jim Pospichal (Bug Ware, US)
Hey jkell, if not D. pentaradiatus or the related D. ono, what do believe it is?
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J Kell (Lincoln Nebraska, US)
I didn't phrase my original statement the best. I should have explained myself. I only meant that I would have gone with the other names that have been mentioned now (D. ono and D. misconceptus). It seems clear that the specimens pictured have rays that behave as seperate crystals, it's just that when the name pentaradiatus comes to mind I always associate the bifurcated tips with that name too.
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Jim Pospichal (Bug Ware, US)
No problem. Was just curious if you had an alternate interpretation of the fossils. As far as bifurcations go, it could be that they are just not preserved in these specimens...i.e., the preservational artefact problem mentioned above. In regards to D. ono, Mike, is there some kind of metric we can use (e.g., length of free rays vs. width of central area)?
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Mike Styzen (Noble Energy, US)
I just looked up my description for D. ono in the Leg 135 volume. The lower photo, above, the one with the reallyshort rays,is mine. That's the holotype. That one is more typical. The paratype, not pictured here is a really good one with all the options, including a faint knob in the center. I didn't make that the holotype because good ones like that are hard to find, and I didn't want people to think they had to look like that to fit the species. I haven't thought about that for a really long time... Take a look at the photos with the description and you will see what I mean

[NB The specimen illustrated in Young 1998 and on this page is not the actual  holotype but a very similar specimen - JRY March 2014]
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Mike Styzen (Noble Energy, US)
I've been on the fence myself about the possibility of D. ono being a preservational artifact. Generally they tend to be smaller than the central area of any of the well preserved D. pentaradiatus in the same sample. As I recall, I don't see D. ono all the way up to the extinction of D. pentaradiatus. If I had D. ono in the mix, I would call it At/Below that datum.
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Simon Cole (PetroStrat, UK)
We use Discoaster ono Styzen 1994 for a stubby version of D. pentaradiatus (or D. misconceptus sensu Theodoridis, 1984 as we call it). I would include the bottom two figs in D. ono though would probably sway more towards D. pentaradiatus for the top two. D. ono is probably just a preservation artefact of D. pentaradiatus but it's any easy split to make so we do anyway. Mike did you ever found any stratigraphic significance for the split?
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Mike Styzen (Noble Energy, US)
The specimens I illustrated with the description in the Leg 135 volume were intended to show the typical morphology (the holotype) and one with the longest rays in proportion to the central area that I would include in my species concept (the paratype). That's about as far as I went with it. The specimen illustrated above with the longer rays would not be D. ono.
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