S. radians group
Classification: Coccolithophores -> Discoasterales -> Sphenolithaceae -> Sphenolithus -> S. radians group
Sister taxa: S. capricornutus group, S. dissimilis group, S. moriformis group, S. heteromorphus group, S. predistentus group, S. furcatolithoides group, S. radians group, S. conspicuus group, S. sp.,
|Daughter taxa: (blue => in age window 0-800Ma) |
| Large, robust sphenolith with squat, square base and short, sharply tapering spine. |
| Small, with narrow, tapering spine.|
| Medium to large sphenolith with a tall compound spine. Distinguished from Sphenolithus radians by its larger size, more irregular outline and apical cycles that extend laterally beyond the base of the apical spine.|
| Medium to large sized (height 6.6-12.1 µm) with a tall compound spine and square shaped base with equidimensional quadrants. The spine is dark but visible at 0° and characterized by a median suture line; at 45° the spine is brightest. Narrow spine endings up to three times the length of the main sphenolith have been rarely observed (up to 38 µm).|
| Small narrow sphenolith with square base, comprising equidimensional quadrants, and tapering monocrystalline spine that is dark at 0° and bright at 45°.|
| Spinose, dart-shaped sphenolith with a low base comprising a single cycle of triangular quadrants when viewed at 0°. The relatively tall, tapering spine is in extinction at 0° and bright at 45°. The quadrants appear larger, and are extended distally, at 45°.|
| Small to medium sized (height 4.0-9.4 µm) with short spine, narrow triangular shape (dart shaped). Lower quadrants are largest and the compound spine is dark at 0°.|
Citation: Sphenolithus radians group sensu Bown & Dunkley Jones, 2012Rank: species group
Distinguishing features: Eocene to Early Oligocene sphenoliths with compound spines, that are visible but dim at 0° and brightest when at 45° to the polarizing directions.
Farinacci & Howe catalog pages:
Morphology remarks: Sphenolith base typically has four distinct quadrants and is square or tapering. In older forms the spines are compound, becoming duo- or monocrystalline in later-appearing forms, and are usually visible but dim at 0° and brightest when at 45° to the polarizing directions; S. furcatolithoides spines behave slightly differently. Species are differentiated based on overall height and shape, spine size and degree of taper. Sphenolithus furcatolithoides, S. perpendicularis, S. kempii and S. cuniculus form a distinct subgroup with first three/four spines then two separate spines that bifurcate directly above the base. S. strigosus has a duocrystalline spine, a higher spine bifurcation point and is dark at 45°.
The group contains predominantly Eocene forms, namely: S. arthuri, S. conspicuus, S. editus, S. orphanknollensis, S. pseudoradians, S. radians, S. spiniger, S. villae; and in the S. furcatolithoides subgroup: S. cuniculus, S. furcatolithoides, S. perpendicularis, S. kempii, S. strigosus and, tentatively, S. runus.
The morphological data given here can be used on the advanced search page. See also these notes
|Metrics||Lith size: 3->11µm; |
Last occurrence (top): in lower part of Chattian Stage (25% up, 26.8Ma, in Chattian stage). Data source: Total of range of species in this database
First occurrence (base): in lower part of Ypresian Stage (22% up, 54.2Ma, in Ypresian 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. For the customisable plot option go to a genus page Parent: Sphenolithus
Bown, P. R. & Dunkley Jones, T. (2012). Calcareous nannofossils from the Paleogene equatorial Pacific (IODP Expedition 320 Sites U1331-1334). Journal of Nannoplankton Research. 32(2): 3-51. gs V O