Nannotax3 - ntax_cenozoic - Tribrachiatus lunatus Nannotax3 - ntax_cenozoic - Tribrachiatus lunatus

Tribrachiatus lunatus

Classification: ntax_cenozoic -> Nannolith families inc sed -> Rhomboasteraceae -> Tribrachiatus -> Tribrachiatus lunatus
Sister taxa: T. contortus, T. digitalis, T. orthostylus, T. absidatus, T. lunatus, T. sp.


Citation: Tribrachiatus lunatus Self-Trail et al. 2017
Rank: Species

Distinguishing features:
Parent taxon (Tribrachiatus): Solid nannoliths with three rays that typically have terminal bifurcations.
This taxon: one arm reduced to short knob, the others curved giving recent-shape, tips pointed.

Farinacci & Howe catalog pages: T. lunatus *


Medium to large, triradiate nannolith with two curved arms of equal length and a third arm that forms a small nub, occasionally curved, that lies midway between the two other arms. Ray tips of the two main arms typically taper to a sharp point and width between ray tips is <15μm. When oriented so that the small third arm is facing upward towards the lens, it has bright birefringence colors (often green or pink), and the specimen looks like a marquise diamond ring (Pl. 2, fig. 13). The crescent shape in larger specimens is somewhat flattened when compared to smaller specimens, which are more rounded. Specimens are commonly overgrown and so exhibit high-order birefringence colors (Pl. 2, fig. 13).
Tribrachiatus lunatus differs from T. absidatus by having a rounded interior that is crescent shaped and a smaller third arm. Additionally, T. lunatus lacks the bent arm tips that are present in T. absidatus. It can sometimes be difficult to distinguish between overgrown specimens of T. lunatus and T. absidatus using XPL, but is easier using phaase contrast. Although curved specimens of T. orthostylus can sometimes be mistaken for T. lunatus if viewed from an odd angle, T. orthostylus typically has a much lower order birefringence color than does T. lunatus and is usually gray in color. [Self-Trail et al. 2017]

Most likely ancestor: Tribrachiatus absidatus - at confidence level 3 (out of 5). Data source: Self-Trail et al. (2017) p.180.

Search data:
LITHS: nannolith-other, nannolith-radiate, horseshoe-shaped, CROSS-POLARS: 1ou, V-prominent,
Lith size: 0->0µm;
The morphological data given here can be used on the advanced search page. See also these notes

Geological Range:
Last occurrence (top): within NP12 zone (50.5-53.7Ma, top in Ypresian stage). Data source: Self-Trail et al. 2017
First occurrence (base): within NP11 zone (53.7-54.17Ma, base in Ypresian stage). Data source: Self-Trail et al. 2017

Plot of occurrence data:


Bramlette, M. N. & Sullivan, F. R. (1961). Coccolithophorids and related nannoplankton of the Early Tertiary in California. Micropaleontology. 7(2): 129-188. 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

Self-Trail, J., Seefelt, E. L., Shepherd, C. L. & Martin, V. A. (2017). Biostratigraphic and morphometric analyses of specimens from the calcareous nannofossil genus Tribrachiatus. Journal of Nannoplankton Research. 37(2-3): 177-188. gs

Shepherd, C. L. & Kulhanek, D. K. (2016). Eocene nannofossil biostratigraphy of the mid-Waipara River section, Canterbury Basin, New Zealand. Journal of Nannoplankton Research. 36(1): 33-59. gs O


Tribrachiatus lunatus compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 2-12-2023

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