Nannotax3 - ntax_cenozoic - S. radians group

Citation: Sphenolithus radians group sensu Bown & Dunkley Jones, 2012

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.

Morphology: 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.

Geological Range:
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

References:

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

Daughter taxa (time control age-window is: 0-800Ma)
				Sphenolithus arthurii Large, robust sphenolith with squat, square base and short, sharply tapering spine.
				Sphenolithus orphanknollensis Small, with narrow, tapering spine.
				Sphenolithus pseudoradians 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.
				Sphenolithus radians 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).
				Sphenolithus richteri Small narrow sphenolith with square base, comprising equidimensional quadrants, and tapering monocrystalline spine that is dark at 0° and bright at 45°.
				Sphenolithus runus 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°.
				Sphenolithus spiniger 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°.

Tags	LITHS:
Metrics	Lith size: 3->11µm;

S. radians group

References:

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