Perissocyclus


Classification: Mesozoic -> Podorhabdales -> Axopodorhabdaceae -> Perissocyclus
Sister taxa: Axopodorhabdus, Cribrocorona, Cribrosphaerella, Dodekapodorhabdus, Ethmorhabdus, Hemipodorhabdus, Hexapodorhabdus, Nephrolithus, Octocyclus, Octopodorhabdus, Perissocyclus, Podorhabdus, Psyktosphaera, Teichorhabdus, Tetrapodorhabdus,

Distinguishing features: Elliptical; central area with one or two cycles of perforations and central hollow spine


Daughter taxa: (blue => in age window 0-300Ma)

Inner cycle of four large pores and outer cycle of 16-18 small pores
Small to medium Perissocyclus (~5µm) with central area grill with less than 10 (originally described as 5-9) perforations in the outer ring.
Large (>7µm) podorhabdids with a central area grill that has an outer cycle of 12 (occasionally 10 to 14) large perforations separated by clearly birefringent struts. An additional inner cycle of perforations may be present, but these are not normally visible in the LM. The bars adjoining the central spine may be thickened to form buttresses.
Large podorhabdid (generally >10µm) with multiple cycles of small perforations, separated by birefringent bars. These perforations are visible in XPL, but only the outer cycle is well enough defined to be easily counted and contains at least 16 perforations (16, 18, and 20 have been observed). The central spine may be supported by buttresses.
Specimens not identified to species level

Taxonomy:

Citation: Perissocyclus Black, 1971
Rank: Genus
Type species: Perissocyclus noeliae Black, 1971.
Synonyms: Duplexipodorhabdus Varol & Girgis 1994 (type species P. plethotretus)

Farinacci & Howe catalog pages: Perissocyclus + *

Distinguishing features: Elliptical; central area with one or two cycles of perforations and central hollow spine


Morphology remarks: Smaller forms (Perrisocyclus fletcheri and Perrisocyclus noeliae) are difficult to differentiate in XPL; their pores can only be counted in phase contrast and only when well-preserved. The larger forms, Perrisocyclus plethotretus and Perrisocyclus tayloriae, are distinctive and potentially useful markers species.

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 Oxfordian Stage (157.25-163.47Ma, base in Oxfordian stage). Data source: Total of range of species in this database

Plot of occurrence data:

References:

Black, M., (1971). Coccoliths of the Speeton Clay and Sutterby Marl. Proceedings of the Yorkshire Geological Society, 38: 381-424.

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.

Varol, O. & Girgis, M., (1994). New taxa and taxonomy of some Jurassic to Cretaceous calcareous nannofossils. Neues Jahrbuch für Geologie und Paläontologie Abhandlungen, 192: 221-253.


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Perissocyclus compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 20-7-2018

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