Cretarhabdaceae


Ancestry: Mesozoic -> Podorhabdales -> Cretarhabdaceae
Sister taxa: Axopodorhabdaceae, Biscutaceae, Calyculaceae, Cretarhabdaceae, Mazaganellaceae, Prediscosphaeraceae, Tubodiscaceae,

Short diagnosis: Regular placoliths; central-area spanned byelevated distal structure typically with cross bars and central spine.
The distal shield usually bicyclic, with narrow outer-cycle and broad inner-cycle; elements usually radial and non-imbricate. LM image is moderately birefringent. V/R structure unclear.


Daughter taxa (blue => in age window 0-300Ma) Granddaughter taxa
Cretarhabdids with central area net that often includes axial cross bars.

Cretarhabdids with relatively broad shields; central area spanned by a broad axial cross, with strong medial extinction lines.

Cretarhabdids with relatively broad shields; central area spanned by blocky diagonal cross; outline may be asymmetric.

Cretarhabdids with relatively narrow shields; central area wide with diagonal cross bars.

Elliptical to subcircular cretarhabdid coccoliths with markedly bicylic rim - outer cycle darker in LM; central area typically narrow with axial or diagonal croos

Cretarhabdids with a distinctly dark image in XPL. The type species has broadly elliptical shields and a narrow central area filled with a broad plate/axial cross; the plate is also dark under XPL but is crossed by at least four extinction lines.

Cretarhabdids with central area spanned by narrow axial cross and fine net.

Cretarhabdids with large, wide, strongly concavo-convex ?proximal shield, narrow ?distal shield and central-area spanned by an axial cross and lateral bars.

Cretarhabdids with a relatively wide central area spanned by an axial cross with lateral bars.

Cretarhabdid with wide central area spanned by a transverse bar.

Taxonomy:

Citation: Cretarhabdaceae Thierstein, 1973
Rank: Family
Type species: Cretarhabdus Bramlette and Martini, 1964.

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

Short diagnosis: Regular placoliths; central-area spanned byelevated distal structure typically with cross bars and central spine.
The distal shield usually bicyclic, with narrow outer-cycle and broad inner-cycle; elements usually radial and non-imbricate. LM image is moderately birefringent. V/R structure unclear.


Morphology remarks: Placoliths with two shields and a central-area spanned by a variety of structures, most commonly, fibrous axial cross-bars with subsidiary lateral bars and a solid central spine or process.
In SEM the distal shield typically appears bicyclic, with a narrow outer-cycle and a dominant, broad inner-cycle, overgrown specimens show however that this is a scissor structure with both elements formed from a single crystal unit with the outer element offset clockwise from the inner element. The proximal shield is unicycle and appears to formed of the same crystal units as the distal shield. The elements are usually radial or near radial and do not appear to imbricate. (our obs.)
In LM the coccolith is moderately birefringent, usually with diagonal isogyres.

Geological Range:
Last occurrence (top): within Maastrichtian Stage (66.04-72.05Ma, top in Maastrichtian stage). Data source: Total of range of species in this database
First occurrence (base): within Toarcian Stage (174.15-182.70Ma, base in Toarcian 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. (Editor), Calcareous nannofossil biostratigraphy. British Micropalaeontological Society Publication Series. Chapman & Hall, pp. 34-85.

Burnett, J.A., (1998). Upper Cretaceous. In: Bown, P.R. (Editor), Calcareous Nannofossil Biostratigraphy. British Micropalaeontological Society Publications Series. Chapman & Hall, London, pp. 132-199.

Thierstein, H.R., (1973). Lower cretaceous calcareous nannoplankton biostratigraphy. Abhandlungen der Geologischen Bundesanstalt, 29: 3-52.


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Cretarhabdaceae compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 24-9-2017

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