Nannotax3 - ntax_mesozoic - Eoconusphaeraceae

Distinguishing features:
Parent taxon (Nannoliths inc sedis): Nannofossils not obviously homologous with heterococcoliths, holococcoliths, or braarudosphaeralids
This taxon: Nannoliths with a truncated-cone-like morphology constructed from an outer rim of thin, elements joined along vertical sutures, and an inner core of numerous radial lamellae that may protrude distally.

Citation: Eoconusphaeraceae Kristan-Tollmann, 1988

The two included Jurassic genera (Eoconusphaera, Conusphaera, plus arguably Calcivascularis) have non-concurrent stratigraphic ranges but very closely comparable morphologies and biogeographies (Bown and Cooper, 1989). Kristan-Tollmann 1988 also included Calcivascularis jansae, which greatly reduces the stratigraphic gap. The taxonomic validity of this grouping is thus uncertain. These forms may prove to be modified heterococcoliths.

Both Conusphaera and Eoconusphaera have an outer rim of vetical laths arranged tangetial to the surface without imbrication or overlap. The core of the nannolith in both cases is formed of steeply dipping, radially-arranged laths, these show clockwise imbrication in Eoconusphaera and anti-clockwise imbrication in Conusphaera, as noted by Moshkovitz (1982). Moreover in C. mexicana the radial laths appear to be organised in two concentric subsets whilst in E. zlambachensis they are organised in 7 or 8 radial wedges, as noted by Posch & Stradner (1987).

See also: Calcivascularis - possibly related genus currently classified in the Parhabdolithaceae;

Geological Range:
Last occurrence (top): in lower part of Aptian Stage (25% up, 123Ma, in Aptian stage). Data source: Total of range of species in this database
First occurrence (base): in mid part of Norian Stage (50% up, 218.9Ma, in Norian stage). Data source: Total of range of species in this database

References:

Bown, P. R. & Cooper, M. K. E. (1989a). Conical nannofossils in the Mesozoic. In, Crux, J. A. & van Heck, S. E. (eds) Nannofossils and their applications: Proceedings of the 2nd INA Conference, London 1987. British Micropalaeontological Society Publication Series. 98-106. gs V O

Bown, P. R. (1998b). Triassic. In, Bown, P. R. (ed.) Calcareous Nannofossil Biostratigraphy. British Micropalaeontological Society Publication Series. 29-33. gs V O

Bown, P. R., Rutledge, D. C., Crux, J. A. & Gallagher, L. T. (1998). Lower Cretaceous. In, Bown, P. R. (ed.) Calcareous Nannofossil Biostratigraphy. British Micropalaeontological Society Publication Series. 86-131. gs O

Kristan-Tollmann, E. (1988b). Coccolithen aus den Älteren Allgäuschichten (Alpiner Lias, Sinemur) von Timor, Indonesien. Geologisch-Paläontologische Mitteilungen Innsbruck. 15: 71-83. gs V O

Moshkovitz, S. (1982). On the findings of a new calcareous nannofossil (Conusphaera zlambachensis) and other calcareous organisms in the Upper Triassic sediments of Austria. Eclogae Geologicae Helvetiae. 75: 611-619. gs V O

Posch, F. & Stradner, H. (1987). Report on Triassic nannoliths from Austria. Abhandlungen der Geologischen Bundesanstalt. 39: 231-237. gs V O

Daughter taxa (time control age-window is: 0-800Ma)		Granddaughter taxa
	Conusphaera Tapering nannoliths with steeply sloping rim and central area filled with a core of radially arranged elements. Most commonly seen in side view. The rim elements are joined along vertical sutures (protolith-rim-like).	Conusphaera mexicana Conusphaera rothii Conusphaera maledicto Conusphaera sinespina Conusphaera sp.
	Eoconusphaera Tall tapering nannoliths with steeply sloping rim and central area filled with a mass of radially arranged elements. LM image shows relatively uniformily birefringent core with axial extinction line.	Eoconusphaera hallstattensis Eoconusphaera zlambachensis Eoconusphaera sp.

Eoconusphaeraceae

References:

Comments (0)

Add Comment