Species arranged in order of first occurence (time control age-window is: 0-800Ma) | Granddaughter taxa | ||||
 | Sphenolithus recolletensis | ||||
 |  |  |  | Sphenolithus strigosus duocrystalline spines that bifurcate high-up on the spine. | |
 |  |  |  | Sphenolithus furcatolithoides Spines diverge just above the base and are near-parallel in the lower part | |
 |  | Sphenolithus shamrockiae Like S. furcatolithoides but with relict central spine - giving cross-shaped extinction figure at 45° | |||
 |  |  |  | Sphenolithus perpendicularis square base with two spines that diverge by around 90° | |
 |  |  |  | Sphenolithus kempii square base with 3 or 4 spines | |
Taxonomy:
Taxonomic discussion: The bifurcating spine is a distinctive character and Shamrock (2010) propsed a lineage of species with hisfeature leading from S. perpendicularis to S. cuniculus. Bown & Dunkley Jones (2012) proposed a similar lineage with slightly different species. Howe (2021) renamed it the S. kempii group after the inferred ancestal species. We prefer to retain the name S. furcatulthides group since furcatolithoides is the best establsihed species and since the name furcatolithoides correctly suggests the inferred relationship with the genus Furcatolithus.
Distinguishing features:
Parent taxon (Sphenolithus): Conical nannoliths with a concave base, consisting of a mass of elements radiating from a common origin.
This taxon: Small Middle Eocene sphenoliths with duocrystaline spines that are dark in the 45° position.
Farinacci & Howe catalog pages:
Morphology: Included within the S. radians group by Bown & Dunkley Jones (2012), these species are characterised by two (rarely more) bifurcating apical spines, bright at 0° and dark at 45°, extending from the upper quadrants. Species differentiation is based on the height and angle of spine bifurcation and size of the basal quadrants. In moderate to poor preservation the upper portion of these tall spines is usually lost, but when well preserved, as seen herein, the entire lith may be preserved, highlighting the extreme spine lengths (up to 25μm; Pl. 11, fig. 25) and variations in upper spine morphology. In the slightly younger, and probably descendant, S. predistentus group, only the lower quadrants are clearly discernable in the basal column and the spines are bright at 45° and diverge in the uppermost part of the spine (e.g. S. obtusus, S. runus, S. predistentus). [Bown & Newsam 2017]
Howe 2021 f1 07.JPG
Howe 2021 f1 08.JPG
Howe 2021 f1 09.JPGMost likely ancestor: S. radians group - at confidence level 3 (out of 5). Data source: Howe 2021, fig 7.
Search data:| Tags | LITHS: |
| Metrics | Lith size: 2->17µm; |
Geological Range:
Last occurrence (top): in lower part of Bartonian Stage (22% up, 40.4Ma, in Bartonian stage). Data source: Total of range of species in this database
First occurrence (base): at base of Lutetian Stage (0% up, 47.8Ma, in Lutetian stage). Data source: Total of range of species in this database
Plot of occurrence data:
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 Howe, R. (2021). Ultrastructure and taxonomy of the family Sphenolithaceae. Journal of Nannoplankton Research. 39(1): 29-75. gsReferences:
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S. furcatolithoides group compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 28-9-2021
Short stable page link: https://mikrotax.org/Nannotax3/index.php?id=1213 Go to Archive.is to create a permanent copy of this page - citation notes |
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