Lithraphidites acutus subsp. eccentricus


Classification: Mesozoic -> Nannoliths inc sedis -> Microrhabdulaceae -> Lithraphidites -> Lithraphidites acutus -> Lithraphidites acutus subsp. eccentricus
Sister taxa: L. acutus subsp. acutus, L. acutus subsp. eccentricus,

Distinguishing features: Lithraphidites with four narrow, triangular processes projecting orthogonally from a position two thirds to three quarters along the main rod.


Taxonomy:

Citation: Lithraphidites acutus subsp. eccentricus Watkins in Watkins & Bowdler, 1984
Rank: Sub-species

Farinacci & Howe catalog pages: Lithraphidites acutum eccentricum * ,

Distinguishing features: Lithraphidites with four narrow, triangular processes projecting orthogonally from a position two thirds to three quarters along the main rod.


Morphology remarks: Lithraphidites acutus eccentricus and Lithraphidites acutus acutus were thought to be palaeobiogeographic variants by Watkins & Bowdler (1984).

Corbett & Watkins (2014), however, argue that eccentricus and acutus are separate species with overlapping ranges but with eccentricus both appearing before acutus and disappearing before it (their text-fig.3). They also suggest redefining the difference between the taxa based on size (eccentricus > ca 10 µm vs. acutus < ca 10 µm) and/or lath structure (bilamellar in eccentricus vs monolamellar in acutus). Lath structure is probably not a good criterion since Janin (1998) presented strong evidence that all Lithraphidites nannoliths have bilamellar structure. 

Geological Range:
Last occurrence (top): within UC4b subzone (94.39-94.44Ma, top in Cenomanian stage). Data source: copied from range of species
First occurrence (base): within UC3a subzone (95.93-96.16Ma, base in Cenomanian stage). Data source: copied from range of species

Plot of occurrence data:

  • (NB There is no histogram as there are no occurrence records for the taxon in the Neptune database) Parent: Lithraphidites acutus

    References:

    Corbett, M. J. & Watkins, D. K. (2014). Cenomanian through basal Coniacian Calcareous Nannofossil biostratigraphy of the Mancos Shale reference section, Mesa Verde National Park, CO. Stratigraphy. 11(1): 97-108. gs

    Watkins, D. K. & Bowdler, J. L. (1984). Cretaceous calcareous nannofossils from Deep Sea Drilling Project Leg 77, southeast Gulf of Mexico. Initial Reports of the Deep Sea Drilling Project. 77: 649-674. gs


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    Lithraphidites acutus subsp. eccentricus compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 16-7-2019

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