Nannotax3 - ntax_cenozoic - Discoaster bellus

Citation: Discoaster bellus Bukry&Percival, 1971

Taxonomic discussion: D. bellus is a name available for non-birefringent symmetrical pentaradial discoasters with simple ray ends, and small central areas. Such forms occur commonly in association with D. hamatus (q.v.), and arguably intergrade with them, but in order to preserve the biostratigraphic value of D. hamatus it is important to separate unambiguous D. hamatus specimens from these more non-descript froms. Also D. bellus type discoasters persist at low abundances after the LO of D. hamatus, and probably gives rise to D. quinqueramus. As noted in the comments, D. prepentaradiatus specimens can also intergrade with D. bellus especially when bifurcations are removed due to dissolution.

Distinguishing features:
Parent taxon (D. pentaradiatus group): Symmetric 5-rayed, late Neogene, discoasters without large proximal boss
This taxon: Symmetric 5-rayed species with simple ray tips

Symmetric 5-rayed species with simple ray tips. Intergrades with D. hamatus, but distinguishing it is useful to avoid recording ambiguous specimens as D. hamatus.

Geological Range:
Notes: FO in NN8, before D. hamatus is discussed in Theodoridis (1984). Blair et al. (2017) document it in more detail and also LAD in lower part of NN11.
Last occurrence (top): in lower part of NN11 zone (20% up, 7.8Ma, in Tortonian stage). Data source: Blair et al. 2017
First occurrence (base): within NN8 zone (10.55-10.89Ma, base in Tortonian stage). Data source: Young 1998; Blair et al. 2017

References:

Blair, S. A., Bergen, J. A., de Kaenel, E., Browning, E. & Boesiger, T. M. (2017). Upper Miocene-Lower Pliocene taxonomy and stratigraphy in the circum North Atlantic Basin: radiation and extinction of Amauroliths, Ceratoliths and the D. quinqueramus lineage. Journal of Nannoplankton Research. 37(2-3): 113-144. gs O

Bukry, D. & Percival, S. F. (1971). New Tertiary calcareous nannofossils. Tulane Studies in Geology and Paleontology. 8: 123-146. gs O

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

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

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

Variants (could also be distinguished informally) (time control age-window is: 0-800Ma)
				Discoaster astellaris Like D. bellus but asymmetric
				Discoaster gemmulatus Like D. bellus but with weak central knob