Cruciplacolithus


Classification: Coccolithophores -> Coccolithales -> Coccolithaceae -> Cruciplacolithus
Sister taxa: Coccolithus, Bramletteius, Campylosphaera, Chiasmolithus, Coronocyclus, Cruciplacolithus, Ericsonia, Solidopons, Birkelundia, Clausicoccus, Craticullithus, Hughesius, Kilwalithus,

Daughter taxa: (blue => in age window 0-800Ma)
Modern and Neogene species
Small modern species, very similar to C. primus
Small Cruciplacolithus species with non-birefringent (sub)axial cross and wide central area
Eocene-Oligocene species
Large (6-10 µm) Cruiplacolithus with narrow shields, wide central area and narrow cross bars that can be axial or rotated.
Small (3.5 µm) Oligocene species with delicate axial cross.
Medium to large sized (~6-10µm), elliptical placolith coccoliths with a low birefringence rim and narrow central area almost filled by broad low birefringence axial cross bars. The brigher tube cycle may be indistinct.
Small to medium sized Cruciplacolithus with narrow shields and wide central area spanned by narrow axial crossbars bearing a spine.
Medium sized Eocene-Oligocene Cruciplacolithus with delicate axial cross
Paleocene species - with rotated cross
Moderate to large Cruciplacolithus with slightly rotated (<20 degrees) cross-bars.
Moderate to large Cruciplacolithus with strongly rotated (>20 degrees) cross-bars.
Moderate to large Cruciplacolithus with slightly rotated (<20 degrees) cross bars that have disjunct, birefringent blocks (‘feet') where they meet the rim.
Paleocene species - with axial cross
Moderate to large (>7 µm) Cruciplacolithus with axially aligned cross bars without feet
Small to moderately sized (Cruciplacolithus with disjunct axial cross-bars.
Circular to subcircular Cruciplacolithus with narrow central area and broad cross-bars.
Medium size to large (>7 µm) Cruciplacolithus with axial cross-bars that have disjunct, birefringent blocks (‘feet') where they meet the rim.
Paleocene species - with distinctive central structure
Cruciplacolithus with narrow cross bars and a delicate net.
Small to moderate Cruciplacolithus with narrow axial cross bars and additional bars that run parallel to the inner edge of the central area.
Small to moderate Cruciplacolithus with a narrow central area almost filled by broad axial cross bars that typically show median extinction lines in XPL.
Specimens which cannot be assigned to established species

Taxonomy:

Citation: Cruciplacolithus Hay & Mohler in Hay et al., 1967
Rank: Genus
Type species: Heliorthus tenuis Stradner, 1961
Variants: These three genera are based on delicate central area structures that are not routinely preserved and cannot be observed in light microscopy. Such structures are rarely preserved, poorly documented and difficult to use in practical taxonomy. They may prove to provide valuable phylogentic data but at the present state of knowledge we prefer to retain Cruciplacolithus in its conventional sense.
Synonyms:
Notes & discussion: Cruciplacolithus is not usually recorded from the Neogene but in well-preserved samples Cocolithus specimens with central crosses are quite frequent. Also small Cruciplacolithus specimens can occasionally be found, as illustrated here from the Pliocene.
The classification of Paleogene Coccolithaceae coccoliths is problematical because of the presence of central area cross-bars across generic groupings (in particular Cruciplacolithus, Coccolithus and Chiasmolithus) that are supposedly characterized by the presence or absence of such bars or particular orientations of bars. Cruciplacolithus is typically defined as having a wide central area spanned by disjunct cross bars that are axially orientated or rotated by up to 20 degrees. Chiasmolithus tends to be used where the cross bars are diagonal.

Distinguishing features: Coccolith central area spanned by disjunct axial cross that may be rotated by up to 20 degrees.

Farinacci & Howe catalog pages: Cruciplacolithus * , Cruciolithus * , Cruciplectus * , Stauronertha * , Catostaura *

Search data:
TagsLITHS: placolith, elliptical, RIM: psh-bicyclic, CA: cross, cross-axial,
CSPH: spherical, monomorphic, V-UNITS: distal shield, px-tube, R-UNITS: c-str, ds-tube, prox shield, DETAILS: ca_disjunct, rim-bicyclic, isogyres oblique,
MetricsLith size: 3->14µm;
Sources:
The morphological data given here can be used on the advanced search page. See also these notes

See also: C. gigas group - Coccolithus species with axial cross;

Geological Range:
Notes: Cruciplacolithus is not usually recorded in the post-Paleocene fossil record but they are present in well-preserved Eocene samples, and Bramletteiusis a closely related Eocene-Oligocene taxon.
Last occurrence (top): Extant Data source: Total of range of species in this database
First occurrence (base): at base of Danian Stage (0% up, 66Ma, in Danian stage). Data source: Total of range of species in this database

Plot of occurrence data:

References:

Hay, W. W., Mohler, H. P., Roth, P. H., Schmidt, R. R. & Boudreaux, J. E. (1967). Calcareous nannoplankton zonation of the Cenozoic of the Gulf Coast and Caribbean-Antillean area, and transoceanic correlation. Transactions of the Gulf Coast Association of Geological Societies. 17: 428-480. gs

Perch-Nielsen, K. (1985a). Cenozoic calcareous nannofossils. In, Bolli, H. M. , Saunders, J. B. & Perch-Nielsen, K. (eds) Plankton Stratigraphy. Cambridge University Press, Cambridge 427-555. gs


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Cruciplacolithus compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 22-10-2019

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Short stable page link: http://mikrotax.org/Nannotax3/index.php?id=378 Go to Archive.is to create a permanent copy of this page - citation notes



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