Biscutum


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

Distinguishing features: 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 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 + + + *

Distinguishing features: 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).


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

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


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Biscutum compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 28-2-2021

Taxon Search:
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Short stable page link: https://mikrotax.org/Nannotax3/index.php?id=10066 Go to Archive.is to create a permanent copy of this page - citation notes



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