|Daughter taxa (time control age-window is: 0-800Ma)||Granddaughter taxa|
Conical nannoliths with a concave base, consisting of a mass of elements radiating from a common origin.
S. moriformis group
S. heteromorphus group
S. delphix group
S. capricornutus group
S. dissimilis group
S. furcatolithoides group
S. radians group
S. anarrhopus group
Middle Eocene and Oigocene sphenoliths with duocrystalline/bifid spines and monocyclic base.
Parent taxon (Discoasterales): Radially symmetrical nannoliths formed from one to several separate cycles of elements that radiate from a common centre or axis.
This taxon: Conical discoasteralids with a concave base, consisting of a mass of elements radiating from a common origin.
Farinacci & Howe catalog pages: Sphenolithaceae [no catalog entry yet]
Morphology: Sphenolith structure: The individual elements of sphenoliths are elongated parallel to their c-axis (this is clear from light microscopy), and consist of three lath-like blades arranged in a Y-shaped form. This morphology is visible in SEMs of specimens from samples with very good preservation, or slight etching. With overgrowth the spaces between the segments become infilled and the elements develop a spinose form. The triple lath form is probably related to the trigonal symmetry of calcite, with laths developing parallel to the x-axes.
The elements radiate from a single origin, which gives the sphenoliths a compact form, and a clear extinction-cross, in polarized light. The proximal part of all sphenolith species is composed of a single cycle of 8 to 16 of these elements. The axes of the proximal elements slope down from the median plane. A concave base is formed by laths from adjacent elements meeting.
The upper half of sphenoliths is normally formed of two or three cycles of elements, radiating from the centre, at decreasing angles to the vertical. The details of the structure are, however, variable; particularly toward the apex, which gives rise to a large amount of species level variation.
See Howe 2021 for updated discussion.
Phylogenetic relations: Sphenoliths first appear in the Palaeocene and go extinct in the mid Pliocene. They show some similarities to Fasciculithaceae and are thought to have similar origins.
|Metrics||Lith size: 2->20µm;|
Last occurrence (top): near base of Piacenzian Stage (14% up, 3.5Ma, in Piacenzian stage). Data source: Total of range of species in this database
First occurrence (base): near top of Danian Stage (90% up, 62.1Ma, in Danian stage). Data source: Total of range of species in this database
Plot of occurrence data:
Deflandre, G. (1952). Classe des Coccolithophoridés. (Coccolithophoridae. Lohmann, 1902). In, Grassé, P. P. (ed.) Traité de Zoologie. Masson, Paris 439-470. gs Perch-Nielsen, K. (1985a). Cenozoic calcareous nannofossils. In, Bolli, H. M., Saunders, J. B. & Perch-Nielsen, K. (eds) Plankton Stratigraphy. Cambridge University Press, Cambridge 427-555. gs
Deflandre, G. (1952). Classe des Coccolithophoridés. (Coccolithophoridae. Lohmann, 1902). In, Grassé, P. P. (ed.) Traité de Zoologie. Masson, Paris 439-470. gs
Perch-Nielsen, K. (1985a). Cenozoic calcareous nannofossils. In, Bolli, H. M., Saunders, J. B. & Perch-Nielsen, K. (eds) Plankton Stratigraphy. Cambridge University Press, Cambridge 427-555. gs
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