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 |
Taxonomy:
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 *
Size:
LITHS: murolith, quadrate, elliptical, CA: ca_conjunct, bar, CROSS-POLARS: V-prominent, rim-unicyclic, |
Lith size: 5->10µm; |
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 (50.50-53.70Ma, 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 (1): 427-555. gsReferences:
Isthmolithus compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 10-12-2024
Short stable page link: https://mikrotax.org/Nannotax3/index.php?id=768 Go to Archive.is to create a permanent copy of this page - citation notes |
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