Nannotax3 - ntax_mesozoic

Nannotax3 - ntax_mesozoic - Biscutum Nannotax3 - ntax_mesozoic - Biscutum

Biscutum

Classification: ntax_mesozoic -> Podorhabdales -> Biscutaceae -> Biscutum
Sister taxa: Biscutum, Discorhabdus, Similiscutum ⟩⟨ Boletuvelum, Chiastella, Crucibiscutum, Gaarderella, Gephyrobiscutum, Helicorhabdus, Jimenezberrocosoia, Seribiscutum, Sollasites

Distinguishing features:
Parent taxon (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.
This taxon: Elliptical 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).

Daughter taxa (time control age-window is: 0-800Ma)		Granddaughter taxa
	long ranging generalised species
	Biscutum constans Small to medium (ca 3-8 µm), elliptical; central area narrow with discrete bright tube cycle and dark core.	Biscutum constans spp. cavum Biscutum constans subsp. cavum
	Biscutum ellipticum Similar to B. constans.
	Late Cretaceous - elliptical
	Biscutum coronum Large (>8µm) Biscutum with moderately narrow central area with clear non-birefringent axial structure and well-developed, bright, inner tube cycle.
	Biscutum dekaenelii Medium (4-6 µm), Central area spanned by a granular cross with hollow central knob
	Biscutum magnum Large (8-10 µm) with vacant central area
	Biscutum melaniae Medium to large (7-10 µm), broadly elliptical, with a wide dark shield and a small, highly birefringent closed central area
	Late Cretaceous - asymmetric
	Biscutum arrogans Small (3-4 µm), asymmetric rim; central area wide, largely filled by 4 plates.
	Biscutum asymmetricum Small (3-4 µm), asymmetric species, with strongly asymmetric proximal shield and weakly asymmetric distal shield. Central area closed by small plates
	Biscutum boletum Medium (5-7 µm), weakly asymmetric with very reduced proximal shield
	Biscutum dissimilis Large (8-11 µm), irregular formed/asymmetric, central area very small, closed, proximal shield reduced.
	Biscutum zulloii Medium sized (5-6 µm), weakly asymmetric, inner tube cycle forms protruding collar.
	Late Cretaceous - elongate
	Biscutum hattneri Medium sized (5-6 µm), lenticular with a wide central area, floored by a plate with a central spine.
	Biscutum notaculum Small (3-5 µm), lenticular central area well-developed, almost closed.
	Biscutum virginica Small (4-5 µm), parallel-sided, closed central area.
	Early Cretaceous species
	Biscutum gaultensis Small (4-5 µm), with well-developed central area with birefringent axial structure.
	Biscutum thurowii Small (3-5 µm), with a small central area lined with blocks and two central-area perforations separated by a birefringent transverse bar aligned with the short ellipse axis.
	Jurassic species
	Biscutum davyi Biscutum with a narrow central area spanned by axial cross bars; the longitudinal bar is particularly broad and tapers towards the the ends of the central area. Bicyclic LM image in XPL.
	Biscutum depravatum Normally elliptical Biscutum with relatively narrow shields and open central area spanned by cross bars slightly rotated from axial. Unicyclic image in XPL.
	Biscutum dorsetensis Circular to subcircular bicyclic Biscutum with a narrow central area and tall spine. Bicyclic image in XPL.
	Biscutum dubium Small, normally elliptical Biscutum with narrow central area. Bicyclic image in XPL.
	Biscutum erismatum
	Biscutum grande Large, normally elliptical Biscutum with relatively broad bright inner cycle and central area spanned by a transverse bar.
	Biscutum intermedium A broadly elliptical Biscutum with a narrow central area spanned by a broad, hollow-spine-bearing, oblique transverse bar. Weakly bicyclic image in XPL.
	Biscutum planum
	Biscutum profundum
	Biscutum sp. Specimens not identified to species level

Taxonomy:

Citation: Biscutum Black in Black & Barnes, 1959

Rank: Genus

Type species: Biscutum testudinariumBlack in Black & Barnes, 1959

Taxonomic discussion: See remarks for family Biscutaceae.

Farinacci & Howe catalog pages: Biscutum + + + *

Morphology:

The distal shield is formed from V-units and the proximal shield and tube cycle are formed from R-units; the distal shield elements are joined along radial or near-radial sutures (+/- 'kinks') and show little or no imbrication. The LM image is generally dark, but bright inner-cycles are common.

Search data:

LITHS: placolith, asymmetric, elliptical, CA: cross-axial, ca_disjunct, process, bar, closed, CROSS-POLARS: rim-bicyclic, V-prominent, R-prominent,

Lith size: 3->11µm;
Data source notes: size range of included species

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 Thanetian Stage (100% up, 56Ma, in Thanetian stage). Data source: Total of range of species in this database
First occurrence (base): at base of Pliensbachian Stage (0% up, 190.8Ma, in Pliensbachian stage). Data source: Total of range 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. See also: customisable plot Parent: Biscutaceae

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