Distinguishing features: Parent taxon (ntax_mesozoic): Mesozoic nannofossils - Cenozoic and extant taxa are in a separate module This taxon: Placolith (or modified placolith) coccoliths showing little or no imbrication. Typically, V-units form distal shield, R-units form proximal shield.
Daughter taxa (time control age-window is: 0-800Ma)
Granddaughter taxa
Axopodorhabdaceae 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
Biscutaceae 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.
Calyculaceae 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.
Cretarhabdaceae Regular placoliths; central-area spanned by elevated distal structure typically with cross bars and central spine. The distal shield usuallyappers to be weakly bicyclic in the SEM, with a narrow outer-cycle and broad inner-cycle; elements usually radial and non-imbricate. LM image is moderately birefringent. V/R structure unclear.
Mazaganellaceae 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.
Prediscosphaeraceae 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.
Tubodiscaceae 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.
Biscutales Aubry 2009, cited in Aubry & Bord (2009)
Prediscosphaerales Aubry, cited in Aubry & Bord (2009)
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.
Distinguishing features: Parent taxon (ntax_mesozoic): Mesozoic nannofossils - Cenozoic and extant taxa are in a separate module This taxon: Placolith (or modified placolith) coccoliths showing little or no imbrication. Typically, V-units form distal shield, R-units form proximal shield.
Morphology: 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.
Search data:
Lith size: 0->0µm;
The morphological data given here can be used on the advanced search page. See also these notes
Geological Range: Last occurrence (top): at top of Paleocene Epoch (100% up, 56Ma, in Thanetian stage). Data source: Total of ranges of the species in this database First occurrence (base): within Sinemurian Stage (192.90-199.46Ma, base in Sinemurian stage). Data source: Total of ranges of species in this database
Plot of occurrence data:
Range-bar - range as quoted above, pink interval top occurs in, green interval base occurs in.
Triangles indicate an event for which a precise placement has been suggested
Neptune data: this is a higher taxon page so Neptune data is not plotted. For the customisable plot option go to a genus page Parent: ntax_mesozoic
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. gsO
Bown, P. R. (1987a). Taxonomy, evolution, and biostratigraphy of Late Triassic-Early Jurassic calcareous nannofossils. Special Papers in Palaeontology. 38: 1-118. gs
Bown, P. R., Rutledge, D. C., Crux, J. A. & Gallagher, L. T. (1998). Lower Cretaceous. In, Bown, P. R. (ed.) Calcareous Nannofossil Biostratigraphy. British Micropalaeontological Society Publication Series . 86-131. gsO
Rood, A. P., Hay, W. W. & Barnard, T. (1971). Electron Microscope Studies of Oxford Clay Coccoliths. Eclogae Geologicae Helvetiae. 64: 245-272. gsO
Young, J. R. & Bown, P. R. (1997). Proposals for a revised classification system for calcareous nannoplankton. Journal of Nannoplankton Research. 19(1): 15-47. gs
Podorhabdales compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 16-10-2024
