Nannotax3 - ntax_mesozoic - Biscutaceae

Biscutaceae


Classification: ntax_mesozoic -> Podorhabdales -> Biscutaceae
Sister taxa: Axopodorhabdaceae, Biscutaceae, Calyculaceae, Cretarhabdaceae, Mazaganellaceae, Prediscosphaeraceae, Tubodiscaceae

Distinguishing features:
Parent taxon (Podorhabdales): Placolith (or modified placolith) coccoliths showing little or no imbrication. Typically, V-units form distal shield, R-units form proximal shield.
This taxon: 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.


Daughter taxa (time control age-window is: 0-800Ma)Granddaughter taxa
Main genera
Biscutum
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).

Discorhabdus
Circular, shields broad, usually without a prominent inner tube cycle; central-area typically narrow, may contain a spine.
D. biradiatus
D. corollatus
D. criotus
D. hannibalis
D. ignotus
D. patulus
D. striatus
D. watkinsii
D. sp.

Similiscutum
Subcircular-elliptical with smooth, grey appearance in XPL and a narrow, bright inner-cycle; central-area narrow and may be empty or spanned by an axial cross.
S. avitum
S. cruciulus
S. finchii
S. novum
S. orbiculus
S. precarium
S. sp.

Gnera with distinctive structures
Boletuvelum
Asymmetric base, with large, hollow, flaring spines, closed distally by a domed covering
B. candens
P. patula sensu Lambert 1993
B. sp.

Chiastella
Elliptical, minute with diagonal cross suporting a hollow spine
C. grana

Crucibiscutum
Elliptical with prominent, birefringent, axial cross.
C. hayi
C. neuquenensis
C. pinnatus
C. ryazanicum
C. salebrosum
C. trilensis
P. quadriperforatus
C. sp.

Gaarderella
Elliptical, large with broad shields; central area wide, spanned by a granular plate.
G. granulifera
G. sp.

Gephyrobiscutum
Elliptical with unicyclic rim; central-area spanned by oblique transverse bar with two distal spikes
G. diabolum
G. sp.

Helicorhabdus
Circular with proximal shield wider than distal; spine with helical structure
H. asymetricus
H. sp.

Jimenezberrocosoia
Elliptical with slits between shield elements and axial cross
J. birchiae
J. bosunensis

Seribiscutum
Elliptical with central-area spanned by broad platelets.
S. bijugum
S. primitivum
S. sp.

Sollasites
Elliptical with relatively wide central-area spanned by complex structure
S. arctus
S. arcuatus
S. bipolaris
S. concentricus
S. falklandensis
S. horticus
S. lowei
S. pristinus
S. thiersteinii
S. sp.

Taxonomy:

Citation: Biscutaceae Black, 1971
Rank: Family

Taxonomic discussion:
The taxonomic significance of conspicuous tube cycles has led to a variety of classification schemes within this family. In a study of the oldest (Early Jurassic) biscutaceans, de Kaenel & Bergen (1993) proposed considerable revision to this family, distinguishing Palaeopontosphaera(arguably a junior synonym of Biscutum) from Biscutum by the presence of a birefringent, distal inner-cycle. The type species holotype (EM) of Biscutum is a proximal view and thus the presence or absence of a tube cycle cannot be determined. Moreover, they argue that the aforementioned holotype is very nearly circular and emend the genus in such a way as to render it equivalent to Bidiscus Bukry, 1969 (?=Discorhabdus Noël, 1965) (i.e., circular to subcircular, unicyclic placoliths). The interpretation of these problematic holotype images is questionable. Here we follow Bown & Young (1997) and Bown (1998) retain the traditional usage of Biscutum, i.e. subcircular to elliptical biscutacean coccoliths which typically have a distal, inner tube cycle.

Farinacci & Howe catalog pages: Biscutaceae [no catalog entry yet]

Distinguishing features:
Parent taxon (Podorhabdales): Placolith (or modified placolith) coccoliths showing little or no imbrication. Typically, V-units form distal shield, R-units form proximal shield.
This taxon: 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.


Morphology: Placoliths with two broad shields that may or may not include a distal inner-cycle (tube cycle). The relatively narrow central areas are vacant, filled with granular calcite or spanned by variably oriented bars or axial cross-bars. 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. Coccospheres are well known and usually spherical or cylindrical.

Search data:
TagsLITHS: placolith,
MetricsLith 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 Thanetian Stage (100% up, 56Ma, in Thanetian stage). Data source: Total of range of species in this database
First occurrence (base): in mid part of Sinemurian Stage (47% up, 195.3Ma, in Sinemurian stage). Data source: Total of range of species in this database

Plot of occurrence data:

References:

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

Bown, P. R. & Young, J. R. (1997). Mesozoic calcareous nannoplankton classification. Journal of Nannoplankton Research. 19(1): 21-36. gs V O

Bown, P. R. (1998a). Calcareous nannofossil biostratigraphy. British Micropalaeontological Society Publication Series. 1-328. gs V O

Bukry, D. (1969). Upper Cretaceous coccoliths from Texas and Europe. University of Kansas Paleontological Contributions, Articles. 51 (Protista 2): 1-79. gs V 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 V O

Noël, D. (1965b). 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


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Biscutaceae compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 18-10-2021

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Short stable page link: https://mikrotax.org/Nannotax3/index.php?id=10065 Go to Archive.is to create a permanent copy of this page - citation notes



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