|Daughter taxa (time control age-window is: 0-800Ma)||Granddaughter taxa|
Medium-sized (4-7µm), narrowly elliptical to lenticular, arched, central area with 7-11 pairs of lateral bars
Small (3-5 µm); central area wide; R-units often forming high, flaring, collar around central area
Small (3-5 µm), narrowly elliptical to lenticular. Like H. a arca but smaller and flatter.
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
Very small (2-3µm), narrowly elliptical, bars platy and thickened centrally giving appearance in LM of a longitudinal bar.
Small (2-4.5 µm) Toweius-like species
Specimens which cannot be assigned to any established species
Three addtional species which have been described in Hornbrookina are not included here:
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.
Farinacci & Howe catalog pages: Hornibrookina *
Differentiated from Toweius and Prinsius by
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]
|LITHS: placolith, elliptical, CA: ca_disjunct, grill, |
CSPH: equant, monomorphic,
|Lith size: 2->9µm;|
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:
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
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
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