Sphenoliths are an extinct group of nannoliths. There are numerous species, classified in the single genus Sphenolithus, family Sphenolithaceae (range: Palaeocene - Pliocene). They are of great biostratigraphic value, especially in the Late Oligocene and Early Miocene (See also range chart)

Informal taxon-based term: Sphenolith nannolith formed by the Sphenolithaceae.
Orientation: The concave end of the nannolith is assumed to be proximal/basal.

sphenolith terms
Apical cycle upper part of sphenolith, formed of most steeply inclined cycle of elements. Types:
Monocrystalline formed of one crystal-unit; e.g. S. heteromorphosus, S. belemnos.
Duocrystalline formed of two crystal-units; e.g. S. distentus, S. furcatulithoides.
Compound formed of several crystal-units; e.g. S. radians, S. abies.
Apical spine elongate extension of apical cycle.
Base all of sphenolith except the apical spine.
Blade one of three sub-parts of an element, only seen in well preserved material.
Core centre of radiation of elements.
Element basic component of sphenoliths, each element appears to be a single crystal-unit.
Lateral cycles cycles between apical and proximal cycles, not always present.
Proximal cycle lowermost cycle of elements.
Upper/lower part part above/below the core.

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