Sphenolithus


Ancestry: Coccolithophores -> Discoasterales -> Sphenolithaceae -> Sphenolithus
Sister taxa: Sphenolithus,

Short diagnosis: Conical nannoliths with a concave base, consisting of a mass of elements radiating from a common origin.


Daughter taxa (blue => in age window 0-300Ma) Granddaughter taxa
Sphenoliths without prominent apical spines.

Late Oligocene - Early Miocene sphenoliths with apical spines formed from a single element.

Middle Eocene and Oigocene sphenoliths with duocrystalline spines and monocyclic base

Small Middle Eocene sphenoliths with duocrystaline spines

Eocene to Early Oligocene sphenoliths with compound spines, that are visible but dim at 0° and brightest when at 45° to the polarizing directions.

Late Paleocene and Early Eocene sphenoliths with monocrystalline spines

Specimens which cannot be assigned to established species

Taxonomy:

Citation: Sphenolithus Deflandre in Grassé, 1952
Rank: Genus
Synonyms:
Notes & discussion: More than 40 species of Sphenolithus have been described. We subdived them here into informal groups which we believe represent clusters of closely related species. The primary criteria are the nature of the spine which may be barely developed (moriformis group), formed of numerous elements (radians group) two elements (predistentus and furcatolithoides groups) or a single element (conspicuus and heteromorphus groups). In addition the base may be formed of several cycles of elements (most groups) or only one cycle (predistentus group).
See also - Perch-Nielsen 1985; Aubry 1989; Maiorano & Monechi 1997

Farinacci & Howe catalog pages: Furcatolithus * Nannoturbella * Sphenolithus *

Short diagnosis: Conical nannoliths with a concave base, consisting of a mass of elements radiating from a common origin.


Morphology remarks: 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.

Geological Range:
Last occurrence (top): within Piacenzian Stage (2.59-3.60Ma, top in Piacenzian stage). Data source: Total of range of species in this database
First occurrence (base): within Danian Stage (61.61-66.04Ma, base in Danian stage). Data source: Total of range of species in this database

Plot of occurrence data:

References:

Aubry, M.-P., (1989). Handbook of Cenozoic calcareous nannoplankton. Book 3: Ortholithae (Pentaliths, and others), Heliotithae (Fasciculiths, Sphenoliths and others). Micropaleontology Press, American Museum of Natural History, New York, 279 pp.

Deflandre, G., (1952). Classe des Coccolithophoridés. (Coccolithophoridae. Lohmann, 1902). In: Grassé, P.P. (Editor), Traite de Zoologie. Masson, Paris, pp. 439-470.

Maiorano, P. & Monechi, S., (1997). New Early Miocene species of Sphenolithus Deflandre, 1952 from the North Atlantic Ocean. Journal of Nannoplankton Research, 19(2): 103-107.

Martini, E., (1965). Mid-Tertiary calcareous nannoplankton from Pacific deep-sea cores. Colston Papers, 17: 393-411.

Perch-Nielsen, K., (1985). Cenozoic calcareous nannofossils. In: Bolli, H.M., Saunders, J.B. and Perch-Nielsen, K. (Editors), Plankton Stratigraphy. Cambridge University Press, Cambridge, pp. 427-555.

Wilcoxon, J.A., (1970). Sphenaster new genus, a Pliocene calcareous nannofossil from the tropical Indo-Pacific. Tulane Studies in Geology and Paleontology, 8: 78-81.


Nannotax3 - Coccolithophores - Sphenolithus by: Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 26-3-2017

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Kenneth M. Towe (Smithsonian Institution emeritus, US)
This old paper should be added to the list of references...

1979 K.M. Towe, Variation and systematics in calcareous nannofossils of the genus Sphenolithus. AMERICAN ZOOLOGIST, v. 19, p. 555-572.

It should give pause to the discussion of various "species" in this genus.
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Jeremy Young (UCL, UK)
good point - do you have a pdf copy of the paper. it would be nice to include your reconstruction of sphenolithus sphere.
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