Nannotax3 - ntax_cenozoic - Discoaster pentaradiatus

Citation: Discoaster pentaradiatus Tan Sin Hok, 1927

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).

Variants:

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

Taxonomic 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.

Distinguishing features:
Parent taxon (D. pentaradiatus group): Symmetric 5-rayed, late Neogene, discoasters without large proximal boss
This taxon: Ray tips with acute bifurcations; strongly concavo-convex; birefringent

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.

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 fig.4 (but rare occurrences reported down to upper NN9 - e.g. Browning et al. (2017)

References:

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

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

Bukry, D. (1973g). Phytoplankton stratigraphy, Deep Sea Drilling Project Leg 20, Western Pacific Ocean. Initial Reports of the Deep Sea Drilling Project. 20: 307-317. gs

Cati, F. & Borsetti, A. M. (1970). I discoasteridi del Miocene delle Marche. Giornale di Geologia. 36(2): 617-652. gs O

Kamptner, E. (1967). Kalkflagellaten - Skelettreste aus Tiefseeschlamm des Südatlantischen Ozeans. Annalen des Naturhistorischen Museums in Wien. 71: 117-198. gs O

Martini, E. & Bramlette, M. N. (1963). Calcareous nannoplankton from the experimental Mohole drilling. Journal of Paleontology. 37(4): 845-855. gs

Müller, C. (1974). Calcareous nannoplankton, Leg 25 (Western Indian Ocean). Initial Reports of the Deep Sea Drilling Project. 25: 579-633. gs

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. 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

Perch-Nielsen, K. (1977). Albian to Pleistocene calcareous nannofossils from the Western South Atlantic, DSDP Leg 39. Initial Reports of the Deep Sea Drilling Project. 39: 699-823. gs O

Raffi, I. et al. (2006). A review of calcareous nannofossil astrobiochronology encompassing the past 25 million years. Quaternary Science Reviews. 25: 3113-3137. gs

Salomon, R. (1999). The Calcite Palace. Website - https://ina.tmsoc.org/galleries/CalcitePalace/index.htm. -. gs

Samtleben, C. (1978). Pliocene-Pleistocene coccolith assemblages from Sierra Leone Rise - Site 366, Leg 41. Initial Reports of the Deep Sea Drilling Project. 41(16): 913-931. gs

Tan Sin Hok, (1927). Discoasteridae incertae sedis. Proceedings of the Koninklijke Nederlandse Akademie van Wetenschappen. Sect Sci, 30: 411-419. gs

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

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

Comments (8)

J Kell(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]

23 May 2012 00:00

Jim Pospichal(US)

Hey jkell, if not D. pentaradiatus or the related D. ono, what do believe it is?

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.

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)?

Mike Styzen(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]

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.

Simon Cole(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?

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.

24 May 2012 00:00

Discoaster pentaradiatus

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