Nannotax3 - ntax_cenozoic - Tribrachiatus absidatus Nannotax3 - ntax_cenozoic - Tribrachiatus absidatus

Tribrachiatus absidatus

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


Citation: Tribrachiatus absidatus 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 <½ length of the other two, the others slightly curved, tips bent and pointed.

Farinacci & Howe catalog pages: T. absidatus *


A medium to large, triradiate nannolith having two straight to slightly curved arms of equal length that exhibit a 95–140° bend near their pointed tips, and a smaller third arm that is less than half the length of the two main arms. The interior angle is between 110–140°. Width between ray tips is typically <15μm. Specimens are commonly overgrown and so exhibit high-order birefringence colors.

Tribrachiatus absidatus exhibits a broad range of morphological variation, and overgrowth can make it difficult to distinguish it from broken specimens of T. orthostylus and T. lunatus. Tribrachiatus absidatus can be differentiated from T. lunatus by the presence of a vaulted interior angle rather than a crescent arc and by the presence of bent tips at the end of the two main arms. Typically, the third arm of T. absidatus is slightly longer than the third arm of T. lunatus.

Most likely ancestor: Tribrachiatus orthostylus - at confidence level 3 (out of 5). Data source: Self-Trail et al. (2017) p. 180.
Likely descendants: Tribrachiatus lunatus; plot with descendants

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:


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

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Short stables page link: Go to to create a permanent copy of this page - citation notes

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