Nannotax3 - Mesozoic - Zeugrhabdotus

Zeugrhabdotus

Classification: Mesozoic -> Eiffellithales -> Chiastozygaceae -> Zeugrhabdotus
Sister taxa: Amphizygus, Archaeozygodiscus, Gorkaea, Placozygus, Reinhardtites, Tranolithus, Zeugrhabdotus, Chiastozygus, Staurolithites, Diadorhombus, Rhabdophidites, Ahmuellerella, Bukrylithus, Diloma, Heteromarginatus, Misceomarginatus, Monomarginatus, Vacherauvillius, Braloweria, Clepsilithus, Crepidolithus, Loxolithus, Neocrepidolithus, Tubirhabdus,

Distinguishing features: Murolith (loxolith) coccoliths with central area spanned by variably constructed transverse bar. The bar is usually spine bearing. Inner/proximal rim cycle is variably developed and so the LM image may be unicyclic or bicyclic. Delicate lateral bars may also be present but are generally only seen in exceptional preservation.

Daughter taxa: (blue => in age window 0-800Ma)
				Unicyclic - small (3-5µm)
				Zeugrhabdotus blowii Unicyclic, small; bar divided longitudinally, darkest at 0°
				Zeugrhabdotus burolletii Unicyclic(?), very small; with additional lateral bars [only known from EM]
				Zeugrhabdotus erectus Unicyclic, small; bar split perpendicular to length; narrow rim/large openings
				Zeugrhabdotus fissus Unicyclic, small; bar divided longitudinally, darkest at 0°
				Zeugrhabdotus moulladei Unicyclic, small; bar complex
				Zeugrhabdotus noeliae Unicyclic (or bicyclic?), small (or medium); bar complex, wide rim/small openings
				Unicyclic - medium (5-8 µm)
				Zeugrhabdotus bicrescenticus Unicyclic, medium; bar divided longitudinally, darkest at 45°; rim broad/openings small
				Zeugrhabdotus diplogrammus Unicyclic, medium; bar divided longitudinally, darkest at 60°
				Zeugrhabdotus fluxus Unicyclic, medium; bar split perpendicular to length, darkest at 45°
				Zeugrhabdotus howei Unicyclic or diffusely bicyclic, medium; bar complex, darkest at 45°
				Zeugrhabdotus petrizzoae Unicyclic, medium; bar divided longitudinally and parts offset , darkest at 45°
				Zeugrhabdotus reticulatus Unicyclic, medium; reticulate net on proximal surface [only known from EM]
				Zeugrhabdotus scutula Unicyclic or diffusely bicyclic, medium-large (6-9µm); bar complex; narrow rim/large openings
				Unicyclic - large (8-12 µm)
				Zeugrhabdotus biperforatus Unicyclic, large; bar divided longitudinally; very wide rim/very small openings
				Zeugrhabdotus burwellensis Unicyclic, small (4-6 µm); bar complex; broad rim/small openings
				Zeugrhabdotus kerguelenensis Unicyclic, large; with very broad spine, often seen in side view; broad rim/small openings
				Bicyclic - small to medium (4-6 µm)
				Zeugrhabdotus clarus Bicyclic, small to medium; bar split perpendicular to length, tapers at both ends.
				Zeugrhabdotus acanthus Bicyclic, medium sized; bar complex, flaring slightly as it meets the rim, can appear x-shaped.
				Zeugrhabdotus trivectis Bicyclic, medium sized (5-6µm); bar complex
				Zeugrhabdotus xenotus Bicyclic, medium sized; bar divided longitudinally, darkest at 0°, can appear x-shaped.
				Bicyclic - medium to large (6-12 µm)
				Zeugrhabdotus angelozziae Diffusely bicyclic, medium-large; bar oblique to length and divided longitudinally
				Zeugrhabdotus cooperi Diffusely bicyclic, medium to large and high; bar split perpendicular to length; broad rim/ narrow openings
				Zeugrhabdotus embergeri Bicyclic, large; bar split perpendicular to length, spine often prominent
				Zeugrhabdotus praesigmoides Bicyclic, medium-large; bar complex; bright inner rim broadest where it meets bridge, very narrow tends of central area.
				Zeugrhabdotus sigmoides Bicyclic, medium-large; bar complex; bright inner rim broadest where it meets bridge, very narrow tends of central area.
				Zeugrhabdotus simplex Bicyclic, large; bar simple (formed of one unit); rim narrow/openings large
				Zeugrhabdotus streetiae Bicycle, large; bar complex, appears x-shaped in some views.
				Zeugrhabdotus sp. Specimens not identified to species level

Taxonomy:

Citation: Zeugrhabdotus Reinhardt, 1965

Rank: Genus

Type species: Zygolithus erectus Deflandre in Deflandre and Fert, 1954, designated by Reinhardt, 1965.

Synonyms:

Glaukolithus Reinhardt 1964 (type species G. diplogrammus)
Microrhabdulinus Deflandre 1963 (cf. Verbeek based on Z. embergeri spines)
Rectapontis Varol & Jakubowski 1989
Lordia Varol & Girgis 1994

Notes & discussion: The taxonomy of Zeugrhabdotus is notoriously confused. We have attempted here to characterise the described species in terms of a limited set of criteria, using both the orginal descriptions and reliably identified images:

Rim structure - whether they appear unicylic (uniformly lowish birefringence) or bicyclic (with a distinctly brighter/higher birefringence inner rim).
Size - most Zeugrhabdotus coccoliths are medium sized (5-8 µm) but we can separate out some smaller and larger species.
Bar structure - three types seem identifiable; divided longitudinally (ie appearing as two parallel bars with a dark median line); split perpendicular to length (i.e.appearing to be tow separate bars meeting in the centre of the coccolith) or complex (more elaborate structures). Bars may also be darkest, (i.e. show least birefringence) when the coccolith is parallel with the polarisers (0° position), or oblique to them (45° position).
Rim width - a few species have either notably wide rims (and so small openings) or notably narrow rims (and so large openings).

Most species can be characterised using these criteria but there are a few problematic names which seem to have been applied with variable meanings - notably Z. erectus, Z. noeliae and Z. burwellensis. These names should be used with caution.
Co-ordinating names between electron microscopy and light microscopy is another problem. On the one hand neither the unicyclic/bicyclic division nor the bar-structure types are easy to apply in EM. on the other hand aspects of structure readily vislble in EM may not be applicable in LM. Consequently most species are only well-known from LM. It would be useful if more SEM studies were undertaken of samples where the taxonomy was well-established in the LM. Conversely there are a couple of species which are only known from the EM - Z. buroletii and Z. reticulatus. [JRY 2020]

Farinacci & Howe catalog pages: Zeugrhabdotus + + * , Glaukolithus + * , Microrhabdulinus * , Lordia * , Rectapontis *

Morphology remarks: Long-ranging group (late Triassic-early Eocene) and often common to dominant.

Search data:

Tags	LITHS: murolith, CA: process, bar, V-UNITS: V-prominent, DETAILS: ca_disjunct, rim-bicyclic, rim-unicyclic,
Metrics	Lith size: 2->14µm; Sources: size range of included species

The morphological data given here can be used on the advanced search page. See also these notes

Geological Range:
Last occurrence (top): at base of Ypresian Stage (1% up, 55.9Ma, in Ypresian stage). Data source: Total of range of species in this database
First occurrence (base): at base of Pliensbachian Stage (0% up, 190.8Ma, in Pliensbachian stage). Data source: Total of range of species in this database

Plot of occurrence data:

Range-bar - range as quoted above, pink interval top occurs in, green interval base occurs in.
Triangles indicate an event for which a precise placement has been suggested
Neptune data: This is a higher taxon page so Neptune data is not plotted. See also: customisable plot Parent: Chiastozygaceae

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

Deflandre, G. & Fert, C. (1954). Observations sur les coccolithophoridés actuels et fossiles en microscopie ordinaire et électronique. Annales de Paléontologie. 40: 115-176. gs

Deflandre, G. (1963). Sur les Microrhabdulidés, famille nouvelle de nannofossiles calcaires. Comptes Rendus Hebdomadaires des Séances de l'Académie des Sciences. Paris. 256: 3484-3487. gs

Reinhardt, P. (1964). Einige Kalkflagellaten-Gattungen (Coccolithophoriden, Coccolithineen) aus dem Mesozoikum Deutschlands. Monatsberichte der Deutschen Akademie der Wissenschaften zu Berlin. 6: 749-759. gs

Reinhardt, P. (1965). Neue Familien für fossile Kalkflagellaten (Coccolithophoriden, Coccolithineen). Monatsberichte der Deutschen Akademie der Wissenschaften zu Berlin. 7: 30-40. gs

Varol, O. & Girgis, M. (1994). New taxa and taxonomy of some Jurassic to Cretaceous calcareous nannofossils. Neues Jahrbuch für Geologie und Paläontologie Abhandlungen. 192: 221-253. gs

Varol, O. & Jakubowski, M. (1989). Some new nannofossil taxa. INA Newsletter. 11: 24-29. gs

Zeugrhabdotus compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 21-2-2020

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Short stable page link: http://mikrotax.org/Nannotax3/index.php?id=11319 Go to Archive.is to create a permanent copy of this page - citation notes

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