Tribrachiatus digitalis


Ancestry: Coccolithophores -> Nannolith families inc sed -> Rhomboasteraceae -> Tribrachiatus -> Tribrachiatus digitalis
Sister taxa: T. contortus, T. digitalis, T. orthostylus, T. sp.,

Short diagnosis: 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.


Taxonomy:

Citation: Tribrachiatus digitalis Aubry, 1996
Rank: Species
Synonyms:
Notes & discussion: Tribrachiatus digitalis intergrades with T. orthostylus.

Farinacci & Howe catalog pages: Tribrachiatus digitalis *

Short diagnosis: 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.

Geological Range:
Notes: According to Shamrock & Watkins 2012 - "The range of T. digitalis occurs within the lower range of T. contortus at Site 762C. This is in agreement of findings of Raffi, Backman and Pälike (2005) and Agnini et al. (2007a), creating a crossover of the NP10a-d subzones of Aubry (1995). Results from these three studies include sites from the Indian, equatorial Pacific and North Atlantic Oceans, and likely indicate a global signal. "
Last occurrence (top): in upper part of NP11 zone (70% up, 53.8Ma, in Ypresian stage). Data source: Agnini et al. 2007 fig 8, 9
First occurrence (base): in upper part of NP10 zone (65% up, 54.8Ma, in Ypresian stage). Data source: Agnini et al. 2007 fig 8, 9

Plot of occurrence data:

References:

Agnini, C.; Fornaciari, E.; Raffi, I.; Rio, D.; Rohl, U. & Westerhold, T., (2007). High-resolution nannofossil biochronology of middle Paleocene to early Eocene at ODP Site 1262: Implications for calcareous nannoplankton evolution. Marine Micropaleontology, 64: 215-248.

Aubry, M.-P., (1996). Towards an Upper Paleocene-Lower Eocene high resolution stratigraphy based on calcarous nannofossil stratigraphy. Israel Journal of Earth-Sciences, 44(239-253).

Bown, P.R., (2005). Palaeogene calcareous nannofossils from the Kilwa and Lindi areas of coastal Tanzania (Tanzania Drilling Project 2003-4). Journal of Nannoplankton Research, 27(1): 21-95.

Bybell, L.M. & Self-Trail, J., (1995). Evolutionary, biostratigraphic and taxonomic study of calcareous nanofossils from a continuous Palaeocene-Eocene boundary section in New Jersey. United States Geological Survey professional paper, 1554: 1-36.

Shamrock, J.L. & Watkins, D.K., (2012). Eocene calcareous nannofossil biostratigraphy and community structure from Exmouth Plateau, Eastern Indian Ocean (ODP Site 762). Stratigraphy, 9(1): 1-11.


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Tribrachiatus digitalis compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 20-8-2017

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Comments (2)

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Jeremy Young (UK)

Marcie

Thanks for the comment, and apologies for the slow reply. The taxonomy of this group has been surprisingly controversial (see brief notes on the Rhomboasteraceae page) and various different combinations have been proposed. The broad consensus emerging from this is that Tribrachiatus and Rhomboaster can usefully be separated, even if they are directly linked by evolution, this reflected in the taxonomy adopted here.

Jeremy

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Marcie Purkey Phillips (US)

It looks like this species has been moved to the genus Rhomboaster (Bybell & Self-Trail 1997, Late Paleocene and Early Eocene Calcareous Nannofossils from three boreholes in an onshore-offshore transect from New Jersey to the Atlantic Continental Rise. Proceedings of the Ocean Drilling Program, Scientific Results, Vol 150X.)

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