Nannotax3 - ntax_cenozoic

Citation: Coccolithophores informal

Taxonomic discussion: Coccolithophore classification is primarily based on the calcareous coccoliths they produce. The structure and mineralogy of coccoliths is very tightly controlled during the, intracellular, coccolith-formation process and so coccolith structure has proven a remarkably robust classification tool, well supported by modern molecular-genetic data. It also means biologists and palaeontologists use the same classification.

There are complications however, most obviously, typical coccolithophores have haplo-diplontic life-cycles with different coccoliths produced in haploid and diploid phases. The diploid phase heterococcoliths have complex structures formed of radial arrays of interlocking crystal units usually with alternating vertical and radial crystallographic orientations (V/R model). The different rim-structures of these heterococcoliths form the essential basis of the classification. The haploid phase holococcoliths are beautifully organised arrays of rhombohedral crystallites, but their morphology is relatively plastic and does not yield useful phylogenetic data. Finally, some other nannofossils occur which do not obviously fit either the heterococcolith or holococcolith model and these are conventionally refered to as nannoliths.

Understanding the classification of coccolithophores thus requires some basic knowledge of coccolithophore life-cycles, biomineralisation, crystallography and optical mineralogy (to interpret cross-polarised light images). A useful overview is provided by Bown & Young (1998) and other references which help explain the system applied here are listed below.

Distinguishing features:
Parent taxon (images):
This taxon: Extant coccolithophores and Cenozoic calcareous nannofossils - Mesozoic nannofossils are in a separate module

Geological Range:
Last occurrence (top): Extant. Data source: Total of range of species in this database
First occurrence (base): at top of No known fossil record modern (100% up, 0Ma, in "Holocene" stage). Data source: Total of range of species in this database

References:

Bown, P. R. & Young, J. R. (1998a). Introduction - calcareous nannoplankton biology. In, Bown, P. R. (ed.) Calcareous Nannofossil Biostratigraphy. British Micropalaeontological Society Publication Series . 1-15. gs

Young, J. R., Didymus, J. M., Bown, P. R., Prins, B. & Mann, S. (1992). Crystal assembly and phylogenetic evolution in heterococcoliths. Nature. 356: 516-518. gs

Young, J. R. et al. (1997). Guidelines for coccolith and calcareous nannofossil terminology. Palaeontology. 40: 875-912. gs

Young, J. R., Davis, S. A., Bown, P. R. & Mann, S. (1999). Coccolith ultrastructure and biomineralisation. Journal of Structural Biology. 126: 195-215. gs

Young, J. R., Geisen, M., Cros, L., Kleijne, A., Probert, I. & Ostergaard, J. B. (2003). A guide to extant coccolithophore taxonomy. Journal of Nannoplankton Research. S1: 1-132. gs

Young, J. R., Geisen, M. & Probert, I. (2005). A review of selected aspects of coccolithophore biology with implications for palaeobiodiversity estimation. Micropaleontology. 51(4): 267-288. gs

Daughter taxa (time control age-window is: 0-800Ma)		Granddaughter taxa
	Heterococcoliths
	Isochrysidales 2N: Mostly placolith heterococcoliths with R-unit dominant. Non-motile N: non-calcifying, motile, with vestigial haptonema.	Noelaerhabdaceae Prinsiaceae Isochrysidaceae
	Coccolithales 2N: Mostly placolith heterococcoliths with V-unit forming the distal shield; R-unit the proximal shield. Non-motile N: Form holococcoliths formed of single block, or non-calcifying	Coccolithaceae Calcidiscaceae Hymenomonadaceae Pleurochrysidaceae
	Zygodiscales 2N: Heterococcoliths with V-units forming upper/outer cycle of imbricated elements and R-units forming basal plate and central mass of irregular elements. Usually motile N: Form holococcoliths formed of single block	Helicosphaeraceae Pontosphaeraceae Zygodiscaceae
	Syracosphaerales 2N: Coccoliths with radial lath cycle of T-units, and disjunct, often complex, axial structure, coccospheres often polymorphic, usually motile N: Form holococcoliths, highly variable	Calciosoleniaceae Rhabdosphaeraceae Syracosphaeraceae
	Coccolith families inc sed 2N: Various heterococcolith groups not obviously related to the well-defined orders N: mostly unknown	Alisphaeraceae Papposphaeraceae Umbellosphaeraceae narrow rimmed placoliths Coccolith genera inc sed Unidentified heterococcoliths
	Mesozoic Survivors Mesozoic taxa which occur in low abundances in the early Palaeogene.	Biscutaceae Chiastozygaceae Markalius Watznaueriaceae
	Holococcoliths & Nannoliths
	Holococcoliths Haploid life-cycle stages, with liths formed of numerous rhombohedral microcrystals	tubeless convex bridged flat-topped septate open-tube fossil holococcoliths Unidentified extant holococcolith
	Braarudosphaerales 2N(?) cell covered by pentaliths (plates formed of 5 segments with lamellar sub-structure) formed extracellualrly N: cell motile, covered by scales	Braarudosphaeraceae
	Discoasterales Radially symmetrical nannoliths formed from one to several separate cycles of elements that radiate from a common centre or axis.	Discoasteraceae Fasciculithaceae Heliolithaceae Sphenolithaceae
	Nannolith families inc sed Haptophytes forming calcareous structures not obviously homologous with heterococcoliths, holococcoliths, or discoasteralids	Ceratolithaceae Lapideacassaceae Lithostromationaceae Nannolith genera inc sed Rhomboasteraceae

Cenozoic and Modern Coccolithophores

References:

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