Distinguishing features: 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 (>8 µm) cruciform nannoliths with high curving ridges running from the centre to ray tips. | |
BownNewsam-2017-fig3.jpgTaxonomy:
Farinacci & Howe catalog pages: Zygodiscaceae [no catalog entry yet]
Distinguishing features: 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.
Size: Coccoliths vary in size from small to very large, mostly medium to large size and including some taxa producing very big coccoliths (e.g. Nannotetrina, Lophodolithus).
| Tags | LITHS: murolith, circular, elliptical, reniform, RIM: outer wall acw-imbricate, CSPH: not known, V-UNITS: c-str, rim, R-UNITS: c-str, inner-rim, none, DETAILS: rim-bicyclic, rim-unicyclic, |
| Metrics | Lith size: 3->30µm; Sources: |
Geological Range:
Last occurrence (top): at top of Chattian Stage (100% up, 23Ma, in Chattian stage). Data source: Total of range of species in this database
First occurrence (base): at base of Danian Stage (0% up, 66Ma, in Danian stage). Data source: Total of range 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, 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, M.N. & Sullivan, F.R., (1961). Coccolithophorids and related nannoplankton of the Early Tertiary in California. Micropaleontology, 7(129-188). 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.References:
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Zygodiscaceae compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 16-12-2018
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