Nannotax3 - ntax_cenozoic - Tribrachiatus Nannotax3 - ntax_cenozoic - Tribrachiatus


Classification: ntax_cenozoic -> Nannolith families inc sed -> Rhomboasteraceae -> Tribrachiatus
Sister taxa: Rhomboaster, Tribrachiatus

Daughter taxa (time control age-window is: 0-800Ma)
Tribrachiatus contortus
Tri-radiate forms with long ray tip bifurcations that deviate strongly from the plane of the nannolith, giving the appearance of two asymmetrically offset and superimposed tri-radiate cycles.
Tribrachiatus digitalis
Single cycle tri-radiate forms with long ray tip bifurcations (around 25% or more of the total arm length). The rays are in the same plane and the bifurcations only slightly deviate from that plane.
Tribrachiatus orthostylus
Large, single-cycle tri-radiate nannoliths with little or no ray end bifurcation (<25% of the total arm length).
Tribrachiatus absidatus
one arm <½ length of the other two, the others slightly curved, tips bent and pointed.
Tribrachiatus lunatus
one arm reduced to short knob, the others curved giving recent-shape, tips pointed.
Tribrachiatus sp.
Specimens which cannot be assigned to any established species


Citation: Tribrachiatus Shamrai, 1963
taxonomic rank: Genus
Type species: Tribrachiatus orthostylus Shamrai, 1963.

Distinguishing features:
Parent taxon (Rhomboasteraceae): Nannoliths with rhombic and tri-radiate morphologies, and non-birefringent images in XPL. Incorporating the genera Rhomboaster and Tribrachiatus.
This taxon: Solid nannoliths with three rays that typically have terminal bifurcations.

Farinacci & Howe catalog pages: Tribrachiatus *

Search data:
LITHS: nannolith-radiate, star-shaped, CROSS-POLARS: 1ou, V-prominent,
Lith size: 8->20µm; Segments: 3->3;
The morphological data given here can be used on the advanced search page. See also these notes

Geological Range:
Last occurrence (top): at top of NP12 zone (100% up, 50.5Ma, in Ypresian stage). Data source: Total of ranges of the species in this database
First occurrence (base): within NP10 zone (54.17-55.86Ma, base in Ypresian stage). Data source: Total of ranges of species in this database

Plot of occurrence data:


Perch-Nielsen, K. (1985). Cenozoic calcareous nannofossils. In, Bolli, H. M., Saunders, J. B. & Perch-Nielsen, K. (eds) Plankton Stratigraphy. Cambridge University Press, Cambridge 427-555. gs

Shamrai, I. A. (1963). Nekotorye formy verkhnemelovykh i paleogenovykh kokkolitov i disko_asterov na yuge russkol platformy [Certain forms of Upper Cretaceous and Paleogene coccoliths and discoasters from the southern Russian Platform]. Izvestiya Vysshikh Uchebnykh Zavedeniy Geologiya i Razvedka. 6(4): 27-40. gs


Tribrachiatus compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 25-2-2024

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

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