Sphenolithus
Classification: ntax_cenozoic -> Discoasterales -> Sphenolithaceae -> Sphenolithus
Sister taxa: Sphenolithus
Towe1979-f8.jpg
Taxonomy:
Citation: Sphenolithus Deflandre in Grassé, 1952Rank: GenusType species: Sphenolithus radians Deflandre in Grassé, 1952Synonyms:
- Furcatolithus Martini, 1965
- Sphenaster Wilcoxon, 1970.
- Nannoturbella Brönnimann & Stradner 1960
Taxonomic discussion: More than 40 species of Sphenolithus have been described. We subdivide them here into informal groups which we believe represent clusters of closely related species, or in some cases single morphologically variable 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).
There has been a tendency toward recognition of ever more sphenolith "species", but it is by no means clear that these reflect biological species, as discussed by Towe (1979).
See also - Perch-Nielsen 1985; Aubry 1989; Maiorano & Monechi 1997.
Distinguishing features: Conical nannoliths with a concave base, consisting of a mass of elements radiating from a common origin.
Farinacci & Howe catalog pages: Sphenolithus * , Furcatolithus * , Sphenaster * , Nannoturbella *
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.
Search data:
| Tags | LITHS: nannolith-radiate, circular, cylindrical, CROSS-POLARS: R-prominent, |
| Metrics | Lith size: 4->20µm; |
The morphological data given here can be used on the advanced search page. See also these notes
Geological Range:
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:
- Range-bar - range as quoted above, pink interval top occurs in, green interval base occurs in.
- Triangles indicate an event for which a precise placement has been suggested
- Neptune data: This is a higher taxon page so Neptune data is not plotted. See also: customisable plot Parent: Sphenolithaceae
References:
Aubry, M. -P. (1989a). 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. 1-279. gs
Deflandre, G. (1952). Classe des Coccolithophoridés. (Coccolithophoridae. Lohmann, 1902). In, Grassé, P. P. (ed.) Traité de Zoologie. Masson, Paris 439-470. gs
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. gs V O
Martini, E. (1965). Mid-Tertiary calcareous nannoplankton from Pacific deep-sea cores. Colston Papers. 17: 393-411. 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
Towe, K. M. (1979). Variation and systematics in calcareous nannofossils of the genus Sphenolithus. American Zoologist. 19: 555-572. gs
Wilcoxon, J. A. (1970b). Sphenaster new genus, a Pliocene calcareous nannofossil from the tropical Indo-Pacific. Tulane Studies in Geology and Paleontology. 8: 78-81. gs V O
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