Hornibrookina elegans Small (3-5 µm); central area wide; R-units often forming high, flaring, collar around central area
Hornibrookina indistincta Small (3-5 µm), narrowly elliptical to lenticular. Like H. a arca but smaller and flatter.
Hornibrookina teuriensis Medium to large (5-10 µm) elliptical; central area with ~10 pairs of lateral bars, and a longitudinal bar, sometimes over-calcified; R units often form ring of nodes around central area
Hornibrookina sp. Specimens which cannot be assigned to any established species
Self-Trail et al 2022 fig 1.jpg
Self-Trail et al 2022 fig 16.jpg
Taxonomy:
Citation: Hornibrookina Edwards, 1973Rank: GenusType species: Hornibrookina teuriensis Edwards, 1973Taxonomic discussion: Coccoliths may be arched and narrowly elliptical to lenticular. Six species have been described but they are all rather similar and possibly should be considered synonyms.
Three addtional species which have been described in Hornbrookina are not included here:
Hornibrookina larae Perez Panera and Ronchi 2021 - we regard this as a junior synonym of Reticulofenestra martinii
Hornibrookina nicolasii Perez Panera and Ronchi 2021 - we believe this species should be recombined in Reticulofenestra
Hornibrookina apellanizii Bernaoloa & Moenchi 2007 - we agree with Self-Trail et al. that this is not a Hornibrookina and probably is a synonym of Centumgemina scissurata, or possibly C.simplex.
Distinguishing features: Parent taxon (Prinsiaceae): Placoliths with R-units forming the lower layer of proximal shield, inner tube and middle tube; V-units forming an upper layer to the proximal shield, outermost tube and the distal shield. In LM they display a dark outer cycle and brighter inner cycle. Central-area structures are conjunct, formed from the R-units. This taxon: Elliptical placoliths with bicyclic distal shields with raised tube cycle and central area grill formed from robust bars.
Morphology: The distal shield and grill are formed of V-units, the proximal shield and inner tube of R-units - this is clear from LMs and the original description. In some species, notably H. edwardsii and H. teuriensis the grill elements may thicken to fill the central area. The tube cycle of R-units may extend above the shield as continuous collar (e.g in H. elegans) or as ring of nodes (e.g. in H. teuriensis). Differentiated from Toweius and Prinsius by
In LM grill is non-birefringent but prominent in phase contrast
In SEM distal view the grill appears disjunct from the tube
In SEM proximal view the proximal shield is formed of a single cycle of elements (without an upper/outer cycle formed from V-units) and the proximal shield is disjunct from the grill
NB This a summary of my observations, primarily form images on this website, they suggest that Hornibrookina should not be included in the Prinsiaceae, but this result has not yet been published [JRY 2022] Size:
Phylogenetic relations: Hornibrookina has long been tentatively placed in the Prinsiaceae (e.g. Perch-Neilsen 1985, Young & Bown 1997) but the coccoliths are atypical. In particular (1) The proximal shield appears to be unicyclic in Hornibrookina whereas in theP rinsicaceae it is bicyclic with an upper/outer cycle of V-units and a lower/inner cycle of R-units (2) The central structure in Hornibrookina appears to be disjunct from the rim whereas it is conjunct with it in the Prinsiaceae. So, this assignment should be re-examined [JRY 2016, updated 2022]
The morphological data given here can be used on the advanced search page. See also these notes
Geological Range: Notes: Abundant in lower Paleocene high latitude settings and conspicuous around the PETM interval. Last occurrence (top): in lower part of Ypresian Stage (22% up, 54.2Ma, in Ypresian stage). 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:
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: Prinsiaceae
References:
Edwards, A. R. (1973b). Key species of New Zealand calcareous nannofossils. New Zealand Journal of Geology and Geophysics. 16: 68-89. gsVO
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
Self-Trail, J. M., Watkins, D. K., Pospichal, J. J. & Seefelt, E. L. (2022). Evolution and taxonomy of the Paleogene calcareous nannofossil genus Hornibrookina. Micropaleontology. 68(1): 85-113. gs
Young, J. R. & Bown, P. R. (1997a). Cenozoic calcareous nannoplankton classification. Journal of Nannoplankton Research. 19(1): 36-47. gsVO
Hornibrookina compiled by Jeremy R. Young, Paul R. Bown, Jacqueline A. Lees viewed: 25-9-2022
Comments
(0)