Nannotax3 - ntax_mesozoic - Cretarhabdaceae

Cretarhabdaceae


Classification: ntax_mesozoic -> Podorhabdales -> Cretarhabdaceae
Sister taxa: Axopodorhabdaceae, Biscutaceae, Calyculaceae, Cretarhabdaceae, Mazaganellaceae, Prediscosphaeraceae, Tubodiscaceae

Distinguishing features:
Parent taxon (Podorhabdales): Placolith (or modified placolith) coccoliths showing little or no imbrication. Typically, V-units form distal shield, R-units form proximal shield.
This taxon: Regular placoliths; central-area spanned by elevated distal structure typically with cross bars and central spine.
The distal shield usuallyappers to be weakly bicyclic in the SEM, with a narrow outer-cycle and broad inner-cycle; elements usually radial and non-imbricate. LM image is moderately birefringent. V/R structure unclear.


Daughter taxa (time control age-window is: 0-800Ma)Granddaughter taxa
Mattiolia
Cretarhabdids with a distinctly dark image in XPL. The type species has broadly elliptical shields and a narrow central area filled with a broad plate/axial cross; the plate is also dark under XPL but is crossed by at least four extinction lines.
Mattiolia furva
Mattiolia sp.

Wisea

Wisea sanjuanensis

Lateral bar in central area
Speetonia
Cretarhabdid with wide central area spanned by a transverse bar.
Speetonia colligata
Speetonia sp.

Cross in central area
Cruciellipsis
Cretarhabdids with relatively broad shields; central area spanned by a broad axial cross, with strong medial extinction lines.
Cruciellipsis cuvillieri
Cruciellipsis sp.

Flabellites
Cretarhabdids with relatively broad shields; central area spanned by blocky diagonal cross; outline may be asymmetric.
Flabellites oblongus
Flabellites sp.

Grantarhabdus
Cretarhabdids with relatively narrow shields; central area wide with diagonal cross bars.
Grantarhabdus camaratus
Grantarhabdus coronadventis
Grantarhabdus meddii
Grantarhabdus sp.

Helenea
Elliptical to subcircular cretarhabdids with bicylic rim - outer cycle darker in LM; central area typically narrow with axial or diagonal croos
Helenea chiastia
Helenea conus
Helenea quadrata
Helenea staurolithina
Helenea sp.

Cross and lateral bars/grill in central area
Cretarhabdus
Cretarhabdids with central area net that often includes axial cross bars.
Cretarhabdus conicus
Cretarhabdus inaequalis
Cretarhabdus madingleyensis
Cretarhabdus striatus
Cretarhabdus sp.

Retecapsa
Cretarhabdids with central area spanned by an axial cross with lateral bars.
Retecapsa incompta
Retecapsa angustiforata
Retecapsa beckii
Retecapsa octofenestrata
Retecapsa schizobrachiata
Retecapsa crenulata
Retecapsa surirella
Retecapsa escaigii
Retecapsa ficula
Retecapsa sp.

Pickelhaube
Cretarhabdids with large, wide, strongly concavo-convex ?proximal shield, narrow ?distal shield and central-area spanned by an axial cross and lateral bars.
Pickelhaube furtiva
Pickelhaube umbellatum
Pickelhaube sp.

Miravetesina
Cretarhabdids with central area spanned by narrow axial cross and fine net.
Miravetesina bergenii
Miravetesina favula
Miravetesina sp.

Taxonomy:

Citation: Cretarhabdaceae Thierstein, 1973
Rank: Family
Type species: Cretarhabdus Bramlette and Martini, 1964.

Farinacci & Howe catalog pages: Cretarhabdaceae [no catalog entry yet]

Distinguishing features:
Parent taxon (Podorhabdales): Placolith (or modified placolith) coccoliths showing little or no imbrication. Typically, V-units form distal shield, R-units form proximal shield.
This taxon: Regular placoliths; central-area spanned by elevated distal structure typically with cross bars and central spine.
The distal shield usuallyappers to be weakly bicyclic in the SEM, with a narrow outer-cycle and broad inner-cycle; elements usually radial and non-imbricate. LM image is moderately birefringent. V/R structure unclear.


Morphology:

Placoliths with two shields and a central-area spanned by a variety of structures, most commonly, fibrous axial cross-bars with subsidiary lateral bars and a solid central spine or process.
In SEM the distal shield typically appears bicyclic, with a narrow outer-cycle and a dominant, broad inner-cycle, overgrown specimens show however that this is a scissor structure with both elements formed from a single crystal unit with the outer element offset clockwise from the inner element. The proximal shield is unicyclic and appears to formed of the same crystal units as the distal shield. The elements are usually radial or near radial and do not appear to imbricate. (our obs.)
In LM the coccolith is moderately birefringent, usually with diagonal isogyres.

The coccolith structure has not been fully worked out but the proimal and distal shield seem to be formed form  a single cycle of crystal units which show moderate birefringence and in plan view oblique isogyres - so they probably have an orientiton which is closest to radial but with significant rotation from truly radial.
In SEM the distal shield often shows a separate cycle around the outer edge but individual elements are often traceable from the main to the outer cycle so this is probably the results of suture kinking/ a scissor-structure rather than a discrete cycle of crystal units. In lm typically the whole coccolith shows a rather uniform moderate brightness, the outer part may be darker but this appears to be due to reduction of thickness at the outer edge, and is seen most obviously in species where the proxmial shield is smaller than the distal shield (e.g. Helenea chiastia). In proximal view the proximal shield is formed of a single cycle of large elements with dextrogyre curvature/dextral obliquity. This contrasts with the proximal side of the distal shield which shows sinistral obliquity. In side views the proximal and distal shields can often be seen to be formed from the same crystal units. The central structures are formed from a mass of small elements. [my interpretation - JRY 2020].

Size:


Ecology & Biogeography


Biology & life-cycles

Phylogenetic relations

Search data:
: placolith,
Lith size: 0->0µm;
The morphological data given here can be used on the advanced search page. See also these notes

Geological Range:
Last occurrence (top): at top of Maastrichtian Stage (100% up, 66Ma, in Danian stage). Data source: Total of range of species in this database
First occurrence (base): at top of Toarcian Stage (95% up, 174.6Ma, in Toarcian stage). Data source: Total of range of species in this database

Plot of occurrence data:

References:

Bown, P. R. & Cooper, M. K. E. (1998). Jurassic. In, Bown, P. R. (ed.) Calcareous Nannofossil Biostratigraphy. British Micropalaeontological Society Publication Series . 34-85. gs O

Burnett, J. A. (1998). Upper Cretaceous. In, Bown, P. R. (ed.) Calcareous Nannofossil Biostratigraphy. British Micropalaeontological Society Publication Series . 132-199. gs O

Grün, W. & Allemann, F. (1975). The Lower Cretaceous of Caravaca (Spain): Berriasian Calcareous Nannoplankton of the Miravetes Section (Subbetic Zone, Prov. of Murcia). Eclogae Geologicae Helvetiae. 68: 147-211. gs O

Thierstein, H. R. (1973). Lower cretaceous calcareous nannoplankton biostratigraphy. Abhandlungen der Geologischen Bundesanstalt. 29: 3-52. gs V O


nannotaxlogo400px

Cretarhabdaceae compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 30-11-2022

Taxon Search:
Advanced Search

Short stable page link: https://mikrotax.org/Nannotax3/index.php?id=10298 Go to Archive.is to create a permanent copy of this page - citation notes



Comments (0)

No comments yet on this page. Please do add comments if you spot any problems, or have information to share

Add Comment

* Required information
1000
Captcha Image
Powered by Commentics