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 0-300Ma)
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): within Toarcian Stage (174.15-182.70Ma, top in Toarcian stage). Data source: Total of range of species in this database
First occurrence (base): within Sinemurian Stage (190.82-199.30Ma, base 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. (Editor), Calcareous nannofossil biostratigraphy. British Micropalaeontological Society Publication Series. Chapman & Hall, pp. 34-85.

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).

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.


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Similiscutum compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 20-7-2018

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