Chiastozygus


Classification: Mesozoic -> Eiffellithales -> Chiastozygaceae -> Chiastozygus
Sister taxa: Amphizygus, Archaeozygodiscus, Gorkaea, Placozygus, Reinhardtites, Tranolithus, Zeugrhabdotus, Staurolithites, Diadorhombus, Rhabdophidites, Ahmuellerella, Bukrylithus, Heteromarginatus, Misceomarginatus, Monomarginatus, Neocrepidolithus, Vacherauvillius, Chiastozygus, Braloweria, Clepsilithus, Crepidolithus, Loxolithus, Tubirhabdus,

Distinguishing features: Murolith (loxolith) coccoliths with relatively narrow rim and wide central area spanned by diagonal bars. Inner/proximal rim cycle is variably developed and so the LM image may be unicyclic or bicyclic.


Daughter taxa: (blue => in age window 0-800Ma)
widely used species
Rim dark, unicyclic; Cross bright, simple
Rim bicyclic with bright inner cycle and strongly curved isogyres; Cross simple
Rim dark unicyclic; Cross complex with distinct median extinction line in XPL.
Rim narrow, bicyclic; Cross thin, bright; Openings large
Rim broad unicyclic or diffusely bicyclic; Cross weakly birefringent
Rim dark unicyclic, narrow; Cross bright with a distinct median extinction line in XPL; Central area wide

less widely used species
Cross H-shaped

Rim dark with median extinction line; Cross with median extinction line, almost fills central opening
Rim bicyclic, bright inner cycle broader; Cross wide, bright and simple; Elongate shape

Rim bicyclic; cross complex, vaulted (centre of cross is above the rim)
Specimens not identified to species level - AND SPECIES OF UNCERTAIN VALUE

Taxonomy:

Citation: Chiastozygus Gartner, 1968
Rank: Genus
Type species: Zygodiscus amphipons Bramlette and Martini, 1964 designated by Gartner, 1968.

Farinacci & Howe catalog pages: Chiastozygus *

Distinguishing features: Murolith (loxolith) coccoliths with relatively narrow rim and wide central area spanned by diagonal bars. Inner/proximal rim cycle is variably developed and so the LM image may be unicyclic or bicyclic.

Geological Range:
Last occurrence (top): at top of Maastrichtian Stage (100% up, 66Ma, in Maastrichtian stage). Data source: Total of range of species in this database
First occurrence (base): at base of Berriasian Stage (0% up, 145Ma, in Berriasian stage). Data source: Total of range of species in this database

Plot of occurrence data:

References:

Bown, P. R., Rutledge, D. C., Crux, J. A. & Gallagher, L. T. (1998). Early Cretaceous. In, Bown, P. R. (ed.) Calcareous Nannofossil Biostratigraphy. British Micropalaeontological Society Publication Series. 86-131. gs

Bramlette, M. N. & Martini, E. (1964). The great change in calcareous nannoplankton fossils between the Maestrichtian and Danian. Micropaleontology. 10(2): 291-322. gs

Gartner, S. (1968). Coccoliths and related calcareous nannofossils from Upper Cretaceous deposits of Texas and Arkansas. The University of Kansas Paleontological Contributions. Article 48 (Protista 1): 1-56. gs


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Chiastozygus compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 18-10-2019

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Short stable page link: http://mikrotax.org/Nannotax3/index.php?id=10246 Go to Archive.is to create a permanent copy of this page - citation notes



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