Nannotax3 - ntax_cenozoic - Isthmolithus Nannotax3 - ntax_cenozoic - Isthmolithus


Classification: ntax_cenozoic -> Zygodiscales -> Zygodiscaceae -> Isthmolithus
Sister taxa: Lophodolithus, Neochiastozygus, Zygodiscus ⟩⟨ Chiphragmalithus, Isthmolithus, Neococcolithes, Nannotetrina

Daughter taxa (time control age-window is: 0-800Ma)
Isthmolithus recurvus
Narrowly elliptical to oblong (or parallelogram-like), relatively high muroliths with two parallel transverse bars.
Isthmolithus rhenanus
Isthmolithus with single, broad, tranverse bar.
Isthmolithus unipons
Narrowly elliptical to oblong (or parallelogram-like), relatively high muroliths with one transverse bar.
Isthmolithus sp.
Specimens which cannot be assigned to any established species


Citation: Isthmolithus Deflandre in Deflandre and Fert, 1954
taxonomic rank: Genus
Type species: Isthmolithus recurvus Deflandre in Deflandre and Fert,1954

Distinguishing features:
Parent taxon (Zygodiscaceae): Muroliths with rim formed from well-developed V- and variably developed R-units, with opposite imbrication directions, and central area structures that include disjunct transverse bars and diagonal crosses. R-units vestigial or not observed in several genera (Chiphragmalithus, Isthmolithus, Neococcolithes).
This taxon: Narrowly elliptical to oblong (or parallelogram-like), relatively high muroliths with one or two transverse bars. R-unit relict or absent and so LM image is unicyclic.

Farinacci & Howe catalog pages: Isthmolithus *

Medium to large (5 to 10 µm), the simpler species I. unipons and I rhenanus are slightly smaller (5-7 µm) than the dominant species I. recurvus (6-10 µm)

Search data:
LITHS: murolith, elliptical, quadrate, CA: ca_conjunct, bar, CROSS-POLARS: rim-unicyclic, V-prominent,
Lith size: 5->10µm;
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 NP22 zone (100% up, 32Ma, in Rupelian stage). Data source: Total of ranges of the species in this database
First occurrence (base): within NP12 zone (50.5-53.7Ma, base in Ypresian stage). Data source: Total of ranges of species in this database

Plot of occurrence data:


Deflandre, G. & Fert, C. (1954). Observations sur les coccolithophoridés actuels et fossiles en microscopie ordinaire et électronique. Annales de Paléontologie. 40: 115-176. gs

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


Isthmolithus compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 10-12-2023

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