Nannoconus


Classification: Mesozoic -> Braarudosphaerales -> Nannoconaceae -> Nannoconus
Sister taxa: Faviconus, Nannoconus, Polycostella,

Distinguishing features: Conical, globular or cylindrical nannoliths composed of plates spirally-arranged around an axial cavity (~>1µm in width) or canal (~<1µm in width). Plate c-axes are arranged tangentially to the longitudinal axis.


Daughter taxa: (blue => in age window 0-800Ma) Granddaughter taxa
Tapering nannoconids with narrow central canal (ct < wt).

Pear-shaped and tapering nannoconids with wide central cavity (ct = 1-3 x wt).

Cylindrical nannoconids with thin, low-angled wall cycles and relatively narrow canal (ct < wt); also may have apical and/or antapical flanges and/or bulbous base

Cylindrical, barrel-shaped or slightly tapering nannoconids with moderately wide central canals (ct ≈ wt).

Cylindrical nannoconids with thin walls (~1.5µm or less), thin, low-angled wall cycles and very wide central cavity (typically ct >3x wt)

Relatively small (<~5µm), subcircular, elliptical or cylindrical nannoconids with relatively narrow canals (ct < wt).

Atypical nannoconids, not fitting in any of the main groups

Specimens not identified to species level

Taxonomy:

Citation: Nannoconus Kamptner, 1931
Rank: Genus
Type species: Nannoconus steinmannii Kamptner, 1931
Synonyms: Brachiolithus Noël (1959)
Nannosphaeroidina Colom 1968

Farinacci & Howe catalog pages: Nannoconus + + * , Brachiolithus * , Nannosphaeroidina *

Distinguishing features: Conical, globular or cylindrical nannoliths composed of plates spirally-arranged around an axial cavity (~>1µm in width) or canal (~<1µm in width). Plate c-axes are arranged tangentially to the longitudinal axis.


Morphology remarks: Nannoconids are particularly common in early Cretaceous Tethyan carbonates. Following abundance declines in the late Barremian to early Aptian they are only occassionally common in younger levels and became extinct in the Campanian. They can be difficult to work with and classify due to intraspecific variability, problems related to microscopical resolution of globose, three-dimensional objects, and poor preservation in the Tethyan limestones, where nannoconids are most common and from which most holotypes were figured. These problems, together with complex palaeobiogeographic patterns, have resulted in rather poor calibration of nannoconid bioevents. For an explanation of general nannoconid morphology and terminology see van Niel (1993, 1994) and Young et al. (1997).

Geological Range:
Last occurrence (top): at top of Campanian Stage (100% up, 72.1Ma, in Campanian stage). Data source: Total of range of species in this database
First occurrence (base): at base of Tithonian Stage (0% up, 152.1Ma, in Tithonian 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

Burnett, J. A. (1998). Upper Cretaceous. In, Bown, P. R. (ed.) Calcareous Nannofossil Biostratigraphy. British Micropalaeontological Society Publication Series. 132-199. gs

Kamptner, E. (1931). Nannoconus steinmanni novo gen., novo spec., ein merkwurdiges gesteinbildendes Mikrofossil aus dem jungeren Mesozoikum der Alpen. Paläontologische Zeitschrift. 13: 288-298. gs

van Niel, B. E. (1993). New observations on the morphology of Nannoconus. In, Hamrsmid, B. & Young, J. R. (eds) Nannoplankton Research. ZPN, Knihovnicha, Hodonin, Cz 73-85. gs

van Niel, B. E. (1994a). A review of the terminology used to describe the genus Nannoconus (calcareous nannofossil, incertae sedis. Cahiers de Micropaleontologie. 9(27-47): -. gs

Young, J. R. et al. (1997). Guidelines for coccolith and calcareous nannofossil terminology. Palaeontology. 40: 875-912. gs


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Nannoconus compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 22-11-2019

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