Nannotax3 - ntax_cenozoic

Citation: Biscutum Black in Black&Barnes, 1959

Type species: Biscutum testudinarium Black, 1959

Synonyms: Palaeopontosphaera Noël, 1965

Taxonomic discussion: Biscutum coccoliths with a small central area filled by a bright plug are a characteristic component of Early Palaeocene assemblages as noted by many authors (e.g Romein 1979, Pospichal 1996, Bown et al. 2023). There is, however, not much agreement on species names. Names based on Danian specimens include Biscutum panis (Edwards 1973) and Biscutum harrisonii Varol 1989, names based on Cretaceous holotypes include Biscutum castrorum Black 1959 and B. melaniae (Gorka 1957), but both these have very poorly illustrated holotypes from significantly older sediments which may represent other species.
B. neocoronum and B. braloweri may represent separate species.

Distinguishing features:
Parent taxon (Biscutaceae): Placoliths with two broad shields; central area narrow; distal shield formed from V-units; proximal shield and tube formed from R-units.
This taxon: Elliptical placoliths with broad shields with or without a prominent inner tube cycle; the central-area may be imperforate or narrow and vacant or spanned by a simple structure (plate, cross or bar).

Geological Range:
Last occurrence (top): at top of CP12 zone (100% up, 46.3Ma, in Lutetian stage). Data source: Total of ranges of the species in this database
First occurrence (base): within Cretaceous Period (66.04-143.10Ma, base in Berriasian stage). Data source: Total of ranges of species in this database

References:

Black, M. & Barnes, B. (1959). The structure of Coccoliths from the English Chalk. Geological Magazine. 96(5): 321-328. gs

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 O

Bown, P. R., Kim, H. & Gibbs, S. J. (2023). Danian calcareous nannofossil evolution and taxonomy with focus on sites from the North Atlantic Ocean (IODP Expedition 342, Sites U1403 and U1407). Journal of Nannoplankton Research. 41(2): 110-157. gs O

de Kaenel, E. & Bergen, J. A. (1993). New Early and Middle Jurassic coccolith taxa and biostratigraphy from the eastern proto-Atlantic (Morocco, Portugal and DSDP Site 547B). Eclogae Geologicae Helvetiae. 86(861-907): -. gs O

Edwards, A. R. (1973b). Key species of New Zealand calcareous nannofossils. New Zealand Journal of Geology and Geophysics. 16: 68-89. gs

Górka, H. (1957). Les Coccolithophoridés du Maestrichtien supérieur de Pologne. Acta Palaeontologica Polonica. 2: 239-284. gs

Noël, D. (1965). Sur les Coccolithes du Jurassique Européen et d'Afrique du Nord. Essai de classification des coccolithes fossiles. Éditions du Centre National de la Recherche Scientifique, Paris. 1-209. gs

Pospichal, J. J. (1996). High latitude calcareous nannofossil changes at the Cretaceous/Tertiary boundary in the southern Indian Ocean. In, Moguilevsky, A. & Whatley, R. (eds) Microfossils and Oceanic Environments. University of Wales, Aberystwyth-Press 205-229. gs

Romein, A. J. T. (1979). Lineages in Early Paleogene calcareous nannoplankton. Utrecht Micropaleontological Bulletin. 22: 1-231. gs O

Daughter taxa (time control age-window is: 0-800Ma)
				Biscutum harrisonii Medium sized, broadly elliptical, bicyclic placolith with a closed central area. The birefringent tube cycle is narrow but conspicuous in XPL.
				Biscutum braloweri Coccoliths medium-sized, central area closed or with narrow opening, coccospheres ovoid to ellipsoidal
				Biscutum neocoronum Species of Biscutum? with a relatively broad distal shield and a small central area characterized by a bright outer ring in phase contrast and polarized light. The inner portion of the central area is dark in phase contrast.
				Biscutum sp. Specimens which cannot be assigned to any established species

Biscutum

References:

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