Zygodiscaceae


Ancestry: Coccolithophores -> Zygodiscales -> Zygodiscaceae
Sister taxa: Helicosphaeraceae, Pontosphaeraceae, Zygodiscaceae,

Short diagnosis: 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).


Daughter taxa (blue => in age window 0-300Ma) Granddaughter taxa
R-units well-developed
Modified muroliths with high walls (higher at one end and forming an asymmetric flange) and wide central area usually spanned by a disjunct, complex tranverse bar.

Muroliths with well-developed V- and R-units and diagonal or asymmetric cross in central-area.

Muroliths with well-developed V- and R-units and transverse bar in central-area. LM image is dominated by bright, broad R-unit inner cycle; V-unit cycle is narrow.

R-units vestigial, central structures septa extending through the coccolith
Muroliths with very high wall (similar to coccolith width) and well-developed central-area cross. V-unit cycle dominates and results in a moderately birefringent unicyclic LM image.

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.

Muroliths with diagonal to H-shaped cross bars. R-unit relict or absent and so LM image is unicyclic.

Typically large cruciform nannoliths with high curving ridges running from the centre to ray tips.

Taxonomy:

Citation: Zygodiscaceae Hay and Mohler, 1967 
Rank: Family

Farinacci & Howe catalog pages:

Short diagnosis: 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).


Morphology remarks: 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 (Zygodiscus, Lophodolithus) and diagonal crosses (Neochiastozygus, Neococcolithes, Chiphragmalithus).
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.

Geological Range:
Last occurrence (top): within Chattian Stage (23.03-28.09Ma, top in Chattian stage). Data source: Total of range of species in this database
First occurrence (base): within Danian Stage (61.61-66.04Ma, base in Danian stage). Data source: Total of range of species in this database

Plot of occurrence data:

References:

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, 381 pp.

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.

Bramlette & Sulivan 1961 [sorry, not in our bibliography yet]

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.

Perch-Nielsen, K., (1985). Cenozoic calcareous nannofossils. In: Bolli, H.M., Saunders, J.B. and Perch-Nielsen, K. (Editors), Plankton Stratigraphy. Cambridge University Press, Cambridge, pp. 427-555.


Nannotax3 - Coccolithophores - Zygodiscaceae by: Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 28-4-2017

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