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
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).
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:
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
Bown, P. R. & Cooper, M. K. E. (1998). Jurassic. In, Bown, P. R. (ed.) Calcareous Nannofossil Biostratigraphy. British Micropalaeontological Society Publication Series . 34-85. gsO
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
Triscutum compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 28-4-2025
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