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
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.
The morphological data given here can be used on the advanced search page. See also these notes
Geological Range: Last occurrence (top): in upper part of Ypresian Stage (67% up, 50.5Ma, in Ypresian stage). Data source: Total of range of species in this database First occurrence (base): in lower part of Ypresian Stage (15% up, 54.7Ma, in Ypresian stage). Data source: Total of range of species in this database
Plot of occurrence data:
Range-bar - range as quoted above, pink interval top occurs in, green interval base occurs in.
Triangles indicate an event for which a precise placement has been suggested
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. gsVO
Tribrachiatus compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 26-3-2023
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