Podorhabdales


Ancestry: Mesozoic -> Podorhabdales
Sister taxa: Arkhangelskiales, Eiffellithales, Stephanolithiales, Podorhabdales, Watznaueriales, Syracosphaerales, Heterococcoliths inc sedis, Holococcoliths, Braarudosphaerales, Nannoliths inc sedis, Mesozoic non–coccoliths, hidden,

Short diagnosis: Placolith (or modified placolith) coccoliths in which the shield elements display little or no imbrication. Typically, V-units form distal shield, R-units form proximal shield.


Daughter taxa (blue => in age window 0-300Ma) Granddaughter taxa
Regular placoliths; central-area, with cross-bars or perforated plate; often with tall, hollow spines.
Distal shield elements non-imbricate V-units; proximal shield and inner cycle formed from R-units. Rim often appears beaded in LM

Regular placoliths; rim broad, central area relatively narrow, with variable central structures.
The distal shield is formed from V-units and the proximal shield and tube cycle are formed from R-units.

Elevated placoliths, tube tall and proximal shield reduced; central-area with variable proximal cover.
The distal shield is formed from V-units and the proximal shield from R-units. Commonly observed in side view.

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.

Three-shielded placoliths; central-area wide, spanned by bars, grill, net or plate.
The distal shield may be high and flaring, formed from non-imbricating elements, joined along radial sutures. LM image is generally dark, but birefringence increases when the distal shield is high.

Regular placoliths; central area spanned by cross-bars supporting a tall, complexely-constructed spine.
The distal shield and proximal shield constructed from 16 large non-imbricating elements (V-units); R-units form restricted cycle on proximal shield and inner tube cycle, giving bicyclic LM image with bright inner cycle.

Elliptical placoliths composed of two narrow shields and a third, narrow, proximally-situated collar cycle that is variable in height. The central-area is broad and open; no central structures have yet been observed. The LM image is dark, although the collar cycle is brighter.

Taxonomy:

Citation: Podorhabdales Rood et al., 1971 emend. Bown, 1987
Rank: Order
Synonyms: These two orders were apparently proposed based on the Prediscosphaeraceae and Biscutaceae, we prefer to keep both families in the Podorhabdales. It is also unlcear from Aubry & Bord (2009) which publications they were proposed in.

Farinacci & Howe catalog pages:

Short diagnosis: Placolith (or modified placolith) coccoliths in which the shield elements display little or no imbrication. Typically, V-units form distal shield, R-units form proximal shield.


Morphology remarks: Placolith (or modified placolith) coccoliths with shields formed from elements that display little or no imbrication and equal development of V and R crystal units, i.e. one shield (distal) formed from V units, the other from R units (proximal). LM images are typically low birefringence but high relief in phase contrast. Shield elements are typically joined along radial sutures, but these may curve or kink. Element curvature is consistently dextrogyre (veeing anticlockwise) and obliquity is broadly dextral (clockwise) in the distal shield, and the same in the proximal shield when viewed proximally.
This order includes the Biscutaceae, Axopodorhabdaceae and other closely related forms. The rim constructions of the Cretarhabdaceae, Tubodiscaceae and Mazaganellaceae are not well understood, and these families are only tentatively assigned to this order.

Geological Range:
Last occurrence (top): within Thanetian Stage (55.96-59.24Ma, top in Thanetian stage). Data source: Total of range of species in this database
First occurrence (base): within Sinemurian Stage (190.82-199.30Ma, base in Sinemurian 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.

Bown, P.R., (1987). Taxonomy, evolution, and biostratigraphy of Late Triassic-Early Jurassic calcareous nannofossils. Special Papers in Palaeontology, 38: 118 p.

Bown, P.R., (1987). The structural development of Early Mesozoic coccoliths and its evolutionary and taxonomic significance. Abhandlung der Geologischen Bundesanstalt, 39: 33-49.

Bown, P.R.; Rutledge, D.C.; Crux, J.A. & Gallagher, L.T., (1998). Early Cretaceous. In: Bown, P.R. (Editor), Calcareous nannofossil biostratigraphy. British Micropalaeontological Society Publication Series. Chapman & Hall, pp. 86-131.

Rood, A.P.; Hay, W.W. & Barnard, T., (1971). Electron Microscope Studies of Oxford Clay Coccoliths. Eclogae Geologicae Helvetiae, 64: 245-272.


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Podorhabdales compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 23-8-2017

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