Nannotax3 - ntax_mesozoic - Triscutum Nannotax3 - ntax_mesozoic - Triscutum

Triscutum


Classification: ntax_mesozoic -> Podorhabdales -> Mazaganellaceae -> Triscutum
Sister taxa: Mazaganella, Triscutum

Distinguishing features:
Parent taxon (Mazaganellaceae): Three-shielded placoliths; central-area wide, spanned by bars, grill, net or plate.
The distal shield may be high and flaring, formed from non-imbricating elements, joined along radial sutures. LM image is generally dark, but birefringence increases when the distal shield is high.

This taxon: Three-shielded placoliths with a wide central-area spanned by a proximal net or grill.


Daughter taxa (time control age-window is: 0-800Ma)
Triscutum beaminsterensis
Large (8-9 µm) Triscutum with broad high distal shield and central area spanned by a perforate net.
Triscutum expansus
Medium (7-8 µm)Triscutum with a wide central area spanned by a net formed from numerous, (~80) thin lateral bars.
Triscutum pricatillus
Medium (6-8 µm) Triscutum with a relatively narrow central area nearly filled by an axial cross structure.
Triscutum sullivanii
Large (7-10 µm) Triscutum with relatively low and narrow shields, vacant central area
Triscutum tiziense
Large (9-12 µm) Triscutum with broad shields and relatively narrow, vacant, central area.
Triscutum sp.
Specimens not identified to species level

Taxonomy:

Citation: Triscutum Dockerill, 1987
taxonomic rank: Genus
Type species: Triscutum beaminsterensis Dockerill, 1987.

Farinacci & Howe catalog pages: Triscutum *

Distinguishing features:
Parent taxon (Mazaganellaceae): Three-shielded placoliths; central-area wide, spanned by bars, grill, net or plate.
The distal shield may be high and flaring, formed from non-imbricating elements, joined along radial sutures. LM image is generally dark, but birefringence increases when the distal shield is high.

This taxon: Three-shielded placoliths with a wide central-area spanned by a proximal net or grill.


Morphology:

Species are often difficult to identify in LM because the distinctive central area structures may be imperceptible or missing. Conversely, several species have been described without observations of central structures (e.g. T. sullivanii, T. tiziense).

Search data:
LITHS: placolith, elliptical, cylindrical, hollow, CA: cross-axial, ca_disjunct, grill, vacant, CROSS-POLARS: R-prominent,
Lith size: 5.5->12µm;
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 Middle Oxfordian Substage (100% up, 156.6Ma, in Oxfordian stage). Data source: Total of ranges of the species in this database
First occurrence (base): within Sinemurian Stage (192.90-199.46Ma, base in Sinemurian stage). Data source: Total of ranges of species in this database

Plot of occurrence data:

References:

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

Dockerill, H. J. (1987). Triscutum, a distinctive new coccolith from the Jurassic. Bulletin des Centres de Recherches Exploration-Production Elf-Aquitaine. 11: 127-131. gs


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Triscutum compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 23-4-2024

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Short stable page link: https://mikrotax.org/Nannotax3/index.php?id=11252 Go to Archive.is to create a permanent copy of this page - citation notes
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