Citation: Tribrachiatus lunatus Self-Trail et al. 2017Rank: 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.
Morphology: 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.
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:
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
(NB There is no histogram as there are no occurrence records for the taxon in the Neptune database) Parent: Tribrachiatus
References:
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. gsO
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. gsO
Tribrachiatus lunatus compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 2-12-2023
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