Polycyclolithaceae


Classification: Mesozoic -> Braarudosphaerales -> Polycyclolithaceae
Sister taxa: Braarudosphaeraceae, Nannoconaceae, Polycyclolithaceae, Other nannoliths with tangential c-axes,

Distinguishing features: Nannoliths composed of two superposed wall cycles and a central-area which may be closed, open and vacant, or spanned by a diaphragm-like structure. Elements have tangential c-axis orientation.


Daughter taxa: (blue => in age window 0-800Ma) Granddaughter taxa
Moderately tall, circular to stellate, multiradiate nannoliths with 5-9 petaloid wall-cycle elements surrounding a wide central area spanned by a median diaphragm. Typically H-shaped in side view.

Near circular to stellate eprolithids with relatively narrow wall formed from 9-16 brick-like, wall-cycle elements surrounding a wide central area spanned by an amedian diaphragm. The wall is usually lower than those seen in Eprolithus.

Eprolithid with narrow wall (formed from 16-24 small, brick-like elements) surrounding a wide central spanned by an amedian diaphragm.

Eprolithids with two cycles of five to seven ray-like, curved, wall-cycle elements surrounding a narrow median diaphragm.

Stellate (triradiate or tetraradiate) nannoliths with three or four ray-like elements; there may be a small central diaphragm.

Stellate to cubiform nannoliths with walls formed from two cycles of 4-9 elements and no central opening or diaphragm. When cubiform, the elements are joined along sutures that go out to the mid-point of the 'cube' edges.

Typically cubiform nannoliths usually formed from two superimposed and complexly-intergrown cycles of four pyramidal/blocky elements each

Nannolith formed of four blocks, nannolith shape is approx square with diagonal sutures, elements show tangential crystallographic orientations

Taxonomy:

Citation: Polycyclolithaceae Forchheimer, 1972 emend Varol, 1992
Rank: Family
Notes & discussion: The Polycyclolithiaceae are tentatively included here in the Braarudospharales (sensu Lees & Bown 2016) since they also have tangential c-axes, and simple rotational symmetry, and the earliest form (e.g. Eprolithus apertior) show simlar cyclindrical shapes to nannoconids. [my interpretation - JRY 2019]
For practical purposes including them here is useful since it groups together all the Mesozoic nanoliths with tangential c-axes. 

Farinacci & Howe catalog pages: Polycyclolithaceae [no catalog entry yet]

Distinguishing features: Nannoliths composed of two superposed wall cycles and a central-area which may be closed, open and vacant, or spanned by a diaphragm-like structure. Elements have tangential c-axis orientation.


Morphology remarks: This family has previously been used for a wide variety of nannoliths with circular to stellate, multiradiate morphologies (e.g. Perch-Nielsen, 1985). Varol (1992) redefined the family to include only those forms which appear to represent a phylogenetic grouping, and this is followed below. Those forms which do not fall into this category are placed in the nannoliths incertae sedis.

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 Kimmeridgian Stage (0% up, 157.3Ma, in Kimmeridgian stage). Data source: Total of range of species in this database

Plot of occurrence data:

References:

Bown, P. R. & Cooper, M. K. E. (1998). Jurassic. In, Bown, P. R. (ed.) Calcareous Nannofossil Biostratigraphy. British Micropalaeontological Society Publication Series. 34-85. gs

Burnett, J. A. (1998). Upper Cretaceous. In, Bown, P. R. (ed.) Calcareous Nannofossil Biostratigraphy. British Micropalaeontological Society Publication Series. 132-199. gs

Forchheimer, S. (1972). Scanning electron microscope studies of Cretaceous coccoliths from the Köpingsberg Borehole No. 1, SE Sweden. Sveriges Geologiska Undersökning; Series C. #668, 65: 1-141. gs

Perch-Nielsen, K. (1985b). Mesozoic calcareous nannofossils. In, Bolli, H. M. , Saunders, J. B. & Perch-Nielsen, K. (eds) Plankton Stratigraphy. Cambridge University Press, Cambridge 329-426. gs

Varol, O. (1992b). Taxonomic revision of the Polycyclolithaceae and its contribution to Cretaceous biostratigraphy. Newsletters on Stratigraphy. 27(93-127): -. gs


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Polycyclolithaceae compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 15-12-2019

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Short stable page link: http://mikrotax.org/Nannotax3/index.php?id=10927 Go to Archive.is to create a permanent copy of this page - citation notes



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