Nannotax3 - ntax_cenozoic - Sphenolithus preasii

Sphenolithus preasii


Classification: ntax_cenozoic -> Discoasterales -> Sphenolithaceae -> Sphenolithus -> S. heteromorphus group -> Sphenolithus preasii
Sister taxa: S. heteromorphus, S. milanetti, S. preasii ⟩⟨ S. pseudoheteromorphus, S. conicus, S. calyculus

Taxonomy:

Citation: Sphenolithus preasii Bergen & de Kaenel, in Bergen et al. 2017
Rank: species
Synonyms:

Distinguishing features:
Parent taxon (S. heteromorphus group): Late Oligocene - Early Miocene sphenoliths with apical spines formed from a single element.
This taxon: Transitional to S. milanetti - base well-eveloped, convex lower surface, shouldered profile.

Farinacci & Howe catalog pages: S. preasii *


Morphology: Medium to large, conical sphenolith. The monocrystalline apical spine is moderate to long (~ ½ to ¾ the total length of the specimen), has a pointed to rounded apex, and becomes extinct when the specimen is aligned with the polarizing direction. In this orientation, the four basal quadrants each appear equant and the height of the upper quadrants is less than the height of the lower quadrants (0.67–0.76 ratio). In lateral profile, the proximal surface is concave and arcuate. The basal lateral periphery appears “bulged”, giving the impression of shoulders when contrasted to the width of the spine at its juncture with the base (most evident at 45° in XPL).

Sphenolithus preasii is somewhat transitional between S. conicus and S. milanetti. It differs from S. conicus by its “bulged” periphery, arcuate proximal surface, and lower upper quadrants

Sphenolithus milanetti also has a “bulged” base, but its base is hemispherical and constructed of much larger elements. The basal upper quadrants (lateral cycle) of S. milanetti is much more reduced than in S. preasii (both height and width) relative to the size of their lower quadrants (proximal cycle).
S. heteromorphus is also similar  butshows uniform taper rather than a shouldered profile, has a linearly indented proximal surface, and the height of its upper and lower quadrants are equal. The lower quadrant elements  of S. heteromorphus appear broad (width > height), whereas those of S. preasii are equant.


Size: L = 5.6–10.0 µm; W = 4.0–6.4 µm (holotype: 9.8mx6.4 µm). [Bergen et al. 2017]

Most likely ancestor: Sphenolithus conicus - at confidence level 3 (out of 5). Data source: Howe 2021 fig8.
Likely descendants: Sphenolithus milanetti; plot with descendants

Search data:
TagsLITHS: nannolith-radiate, circular, cylindrical, CA: process, CROSS-POLARS: R-prominent,
MetricsLith size: 5->10µm;
Data source notes: Bergen et al 2017
The morphological data given here can be used on the advanced search page. See also these notes

Geological Range:
Last occurrence (top): within NN4 zone (14.91-17.95Ma, top in Langhian stage). Data source: Bergen et al 2017
First occurrence (base): within NN3 zone (17.95-19.00Ma, base in Burdigalian stage). Data source: Bergen et al 2017

Plot of occurrence data:

References:

Bergen, J. A., de Kaenel, E., Blair, S. A., Boesiger, T. M. & Browning, E. (2017). Oligocene-Pliocene taxonomy and stratigraphy of the genus Sphenolithus in the circum North Atlantic Basin: Gulf of Mexico and ODP Leg 154. Journal of Nannoplankton Research. 37(2-3): 77-112. gs V O

Howe, R. (2021). Ultrastructure and taxonomy of the family Sphenolithaceae. Journal of Nannoplankton Research. 39(1): 29-75. gs


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Sphenolithus preasii compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 21-9-2021

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Short stable page link: https://mikrotax.org/Nannotax3/index.php?id=1613 Go to Archive.is to create a permanent copy of this page - citation notes



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