Amaurolithus


Classification: Coccolithophores -> Nannolith families inc sed -> Ceratolithaceae -> Amaurolithus
Sister taxa: Amaurolithus, Ceratolithus, Nicklithus, Orthorhabdus, Triquetrorhabdulus,

Daughter taxa: (blue => in age window 0-800Ma)
Like A. delicatus but shorter arms.
Simple horseshoe-shaped amauroliths. Grades into the other morphotypes, especially A. primus and A. tricorniculatus.
Simple form with short arms, broad arch and weakly developed keels.
Right arm extended into apical spur.
Specimens which cannot be assigned to established species

Taxonomy:

Citation: Amaurolithus Gartner and Bukry, 1975
Rank: Genus
Type species: Ceratolithus tricorniculatus Gartner 1967
Notes & discussion: Raffi et al. (1998) documented likely evolutionary relationships between Ceratolithus and the fossil genera Amaurolithus and Triquetrorhabdulus. They presented evidence that A. delicatus, A. amplificus and C. acutus all independently evolved from Triquetrorhabdulus. Since this indicated that Amaurolithus was polypyhletic they proposed dividing the genus in two; Amaurolithus and Nicklithus. This is followed here.

Distinguishing features: Ceratoliths non-birefringent or only weakly birefringent

Farinacci & Howe catalog pages: Amaurolithus *


Morphology remarks: Ceratoliths non-birefringent or only weakly birefringent. The c-axis is perpendicular to the plane of horseshoe, but spines on the surface may result it in being tilted from the horizontal and so showing some birefringence, but birefringence is lower than in Ceratolithus and extinction is rarely exactly in line with axis of the ceratolth.
In the SEM Amaurolithus ceratoliths (sometimes termed amauroliths) usually come to rest with the more ornamented surface upward, in this orientation the left hand arm is distinctly curved whilst the right hand arm is relatively straight, but more heavily ornamented.

Search data:
TagsLITHS: nannolith-other, horseshoe-shaped,
CSPH: not known, V-UNITS: all, DETAILS: 1ou,
MetricsLith size: 5->12┬Ám; Segments: 1->1;
Sources:
The morphological data given here can be used on the advanced search page. See also these notes

Geological Range:
Last occurrence (top): in upper part of Zanclean Stage (82% up, 3.9Ma, in Zanclean stage). Data source: Total of range of species in this database
First occurrence (base): at top of Tortonian Stage (96% up, 7.4Ma, in Tortonian stage). Data source: Total of range of species in this database

Plot of occurrence data:

References:

Gartner, S. & Bukry, D. (1975). Morphology and phylogeny of the coccolithophycean family Ceratolithaceae. Journal of Research of the United States Geological Survey.. 3: 451-465. gs

Raffi, I., Backman, J. & Rio, D. (1998). Evolutionary trends of tropical calcareous nannofossils in the late Neogene. Marine Micropaleontology. 35(1): 17-41. gs

Young, J. R. (1998). Neogene. In, Bown, P. R. (ed.) Calcareous Nannofossil Biostratigraphy. British Micropalaeontological Society Publication Series. 225-265. gs


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Amaurolithus compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 18-9-2019

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Short stable page link: http://mikrotax.org/Nannotax3/index.php?id=40 Go to Archive.is to create a permanent copy of this page - citation notes



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