Similiscutum


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

Distinguishing features: 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.


Daughter taxa: (blue => in age window 0-800Ma)
Small, elliptical, biscutacean placolith with narrow to closed central-area.
Small, broadly elliptical, biscutacean placolith with narrow central area spanned by a small axial cross.
Large Similiscutum with wide shields and very narrow or closed central area. Unicyclic or weakly bicyclic image in XPL with clearly visible elements. A transverse-bar-like structure may be visible in some specimens.
Broadly elliptical Similiscutum with very narrow central area closed by a spine bearing plate. Dark, unicyclic image in XPL with strongly striate shields.
Small, subcircular to circular, biscutacean placolith with narrow to closed central-area.
Small to medium-sized, narrowly elliptical, biscutacean placolith with narrow central area spanned by a small axial cross.
Specimens not identified to species level

Taxonomy:

Citation: Similiscutum de Kaenel & Bergen, 1993
Rank: Genus
Type species: Similiscutum cruciulus de Kaenel and Bergen, 1993.
Notes & discussion: Taxonomic concepts within Similiscutum were revised by Mattioli et al. 2004 - and these are followed here.

Farinacci & Howe catalog pages: Similiscutum + *

Distinguishing features: 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.


Morphology remarks: The inner tube cycle is lower in height than in Biscutum and this results in the relatively dim collar in cross-polarised light (Mattioli et al. 2004).

Geological Range:
Last occurrence (top): at top of Bathonian Stage (100% up, 166.1Ma, in Bathonian 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:

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

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

Mattioli, E., Pittet, B., Young, J. R. & Bown, P. R. (2004). Biometric analysis of Pliensbachian-Toarcian (Lower Jurassic) coccoliths of the family Biscutaceae: intra- and interspecific variability versus palaeoenvironmental influence. Marine Micropaleontology. 52: 5-27. gs


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Similiscutum compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 22-8-2019

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Short stable page link: http://mikrotax.org/Nannotax3/index.php?id=11084 Go to Archive.is to create a permanent copy of this page - citation notes



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