Taxonomy:
Distinguishing features:
Parent taxon (Zygodiscales): 2N: Heterococcoliths with V-units forming upper/outer cycle of imbricated elements and R-units forming basal plate and central mass of irregular elements. Usually motile
N: Form holococcoliths formed of single block
This taxon: 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).
Original description: Diagnosis - Coccoliths consisting of an elliptical ring composed of strongly imbricate laths or tabulae and an open central area spanned by an I-, X-, or H-shaped structure symmetrical about the short axis of the ellipse. Rim dextrogyre in distal view between crossed polarizers.
Farinacci & Howe catalog pages: Zygodiscaceae *
Morphology:
R-units are vestigial or absent in several genera (Chiphragmalithus, Isthmolithus, Neococcolithes, Nannotetrina) and in these genera the central structures are formed of vertical septa that extend from the proximal surface to the distal surface and often protrude above the wall. The nannolith Nannotetrina was long suspected to be related to this group (Bramlette & Sulivan 1961, Perch-Nielsen 1985), by further reduction of the rim and expansion of the central structure, and this was demonstrated by Bown & Newsam (2017) through lineage study in well-preserved material from IODP expedition 342.
Size:
Lith size: 3->30µm; |
Geological Range:
Last occurrence (top): at top of Oligocene Epoch (100% up, 23Ma, in Aquitanian stage). Data source: Total of ranges of the species in this database
First occurrence (base): within NP1 zone (65.47-66.04Ma, base in Danian stage). Data source: Total of ranges of species in this database
Plot of occurrence data:
Aubry, M. -P. (1990). Handbook of Cenozoic calcareous nannoplankton. Book 4: Heliolithae (Helicoliths, Cribriliths, Lopadoliths and others). Micropaleontology Press, American Museum of Natural History, New York. 1-381. gs Bown, P. R. & Newsam, C. (2017). Calcareous nannofossils from the Eocene North Atlantic Ocean (IODP Expedition 342 Sites U1403–1411). Journal of Nannoplankton Research. 37(1): 25-60. gs O Bramlette, M. N. & Sullivan, F. R. (1961). Coccolithophorids and related nannoplankton of the Early Tertiary in California. Micropaleontology. 7(2): 129-188. gs Hay, W. W. & Mohler, H. P. (1967). Calcareous nannoplankton from Early Tertiary rocks at Point Labau, France and Paleocene-Early Eocene correlations. Journal of Paleontology. 41(6): 1505-1541. 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. gs Romein, A. J. T. (1979). Lineages in Early Paleogene calcareous nannoplankton. Utrecht Micropaleontological Bulletin. 22: 1-231. gs OReferences:
Zygodiscaceae compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 8-11-2024
Short stable page link: https://mikrotax.org/Nannotax3/index.php?id=1514 Go to Archive.is to create a permanent copy of this page - citation notes |
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