Nannotax3 - ntax_main - Discoaster exilis

Citation: Discoaster exilis Martini&Bramlette, 1963

Synonyms:

Discoaster extensus Hay in Hay et al. 1967
Discoaster graviterminatus Varol 1984
Discoaster perclarus Hay in Hay et al. 1967

The following three speices described from Malta by SEM are probably best interpreted as overgrown D. exilis

Discoaster gozoensis Hojjatzadeh (1978)
Discoaster prismatica Hojjatzadeh (1978)
Discoaster pugnosa Hojjatzadeh (1978)

Browning et al. (2017) separate D. gozoenis from D. exilis on the grounds that the ridge on the proximal surface of the rays of D. exilis is slightly curved (as mentioned in the original description of Martini & Bramlette (1963). However, forms with straight ridges and curved ridges intergrade and have identical ranges (Browning et al. 2017), hence separating them is pointless.

Variants:

Eu-discoaster protoexilis Theodoridis, 1984 - intermediate to D. deflandrei, large bifurcations, medium central-area. N.B. If this morphotype was distinguished then other names (e.g. D. aulakos Gartner, 1967), might have priority;
Discoaster wisei Wei 2003 - form with large central area
Discoaster exilis var. resolutioniae Fernando et al. 2020 - asymmetric 4-rayed variant, with bird's-foot geometry

Taxonomic discussion: This is the dominant Middle Miocene discoaster and like D. deflandrei shows considerable variation in size, strength of bifurcations, central area size etc. Only variants with particularly strong central area features have been successfully spearated. Browning et al. (2017) disinguished a range of forms and these may prove valuable in some contexts but they are regarded gere as variants and are not reccomended for general use.

Distinguishing features:
Parent taxon (D. exilis group):
This taxon: Small central-area; usually with weak distal and proximal bosses; bifurcations acutely angled in plan-view

6-rayed discoaster; with small central-area; usually with weak distal and proximal bosses. Bifurcations acutely angled in plan-view and wedge-shaped in cross-section. Rays flat and proximal and distal sides virtually identical.

Geological Range:
Last occurrence (top): within NN9 zone (9.53-10.55Ma, top in Tortonian stage). Data source: Young 1998
First occurrence (base): within NN4 zone (14.91-17.95Ma, base in Burdigalian stage). Data source: Young 1998

References:

Bown, P. R. & Dunkley Jones, T. (2012). Calcareous nannofossils from the Paleogene equatorial Pacific (IODP Expedition 320 Sites U1331-1334). Journal of Nannoplankton Research. 32(2): 3-51. gs O

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

de Kaenel, E. & Villa, G. (1996). Oligocene-Miocene calcareous nannofossil biostratigraphy and paleoeecology from the Iberian Abyssal Plain. Proceedings of the Ocean Drilling Program, Scientific Results. 149: 79-145. gs O

Fernando, A. G. S, et al. (2020). Pliocene four-rayed discoasters from IODP Expedition 363 sites in the eastern Indian Ocean and western Pacific Ocean. Journal of Nannoplankton Research. 38(1): 49-55. gs

Gartner, S. (1967a). Calcareous nannofossils from Neogene of Trinidad, Jamaica, and Gulf of Mexico. University of Kansas Paleontological Contributions, Papers. 29: 1-7. gs

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

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

Varol, O. & Bowman, A. R. (2024). The new Middle Miocene genus Olladiscoaster, and related and associated discoasters. Grzybowski Foundation Special Publication. 28: 1-102. 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

Sub-taxa & variants (time control age-window is: 0-800Ma)
				Discoaster caulifloris large stellate stem and wide bifurcations
				Discoaster moorei Asymetric 5-rayed discoaster with bifurcations.
				Discoaster extensus Ray bifurcations curve proximally
				Discoaster discissus Wide, tapering rays with notched tips.
				Discoaster signus Similar to D. petaliformis but with longer bifurcations, and weaker boss.
				Discoaster apetalus Like D. petaliformis but without the central boss

Discoaster exilis

References:

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