Nannotax3 - ntax_cenozoic

Citation: Toweius Hay and Mohler, 1967

Type species: Toweius craticulus Hay and Mohler, 1967, a junior synonym of Toweius pertusus (Sullivan, 1965) Romein, 1979

Synonyms: Girgisia Varol 1989 - proposed as separate genus for T. gammation

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 to circular prinsiacean placoliths with central areas that are typically spanned by a proximal net and/or distal conjunct nets or bars. Typically medium sized.

Intergrade with Prinsius but distinguished by wider,better-developed, central area nets.

Geological Range:
Notes: Toweius was one of the dominant placolith groups of the late Paleocene to early Eocene but declined, broadly coincident with the appearance and rise of the reticulofenestrid group in the early Eocene (zones NP12–13) (e.g., Agnini et al. 2006). The extinction of Toweius has remained poorly constrained with reports ranging from Zone NP12 (Bralower & Mutterlose 1995) to Zone NP15 (Perch-Nielsen, 1985). Relatively common Toweius coccoliths were documented in equatorial Pacific sites up to Zone NP15 by Bown & Dunkley Jones (2012) and similarly we see Toweius through to Subzone NP15b in the Exp. 342 sites (e.g. Site U1409), confirming this later extinction level. [Bown & Newsam 2017]
Last occurrence (top): in upper part of Lutetian Stage (74% up, 42.9Ma, in Lutetian stage). Data source: Total of range of species in this database
First occurrence (base): in upper part of Danian Stage (63% up, 63.2Ma, in Danian stage). Data source: Total of range of species in this database

References:

Agnini, C., Muttoni, G., Kent, D. V. & Rio, D. (2006). Eocene biostratigraphy and magnetic stratigraphy from Possagno, Italy: The calcareous nannofossil response to climate variability. Earth and Planetary Science Letters. 2241: 815-830. gs

Agnini, C., Fornaciari, E., Raffi, I., Rio, D., Rohl, U. & Westerhold, T. (2007a). High-resolution nannofossil biochronology of middle Paleocene to early Eocene at ODP Site 1262: Implications for calcareous nannoplankton evolution. Marine Micropaleontology. 64: 215-248. gs

Agnini, C., Fornaciari, E. & Raffi, I. (2008). Three new species of calcareous nannofossil from Late Palaeocene and Early Eocene assemblages (Ocean Drilling Program Site 1262, Walvis Ridge, SE Atlantic Ocean). Journal of Nannoplankton Research. 30(1): 51-56. gs

Bown, P. R. & Dunkley Jones, T. (2012). Calcareous nannofossils from the Paleogene equatorial Pacific (IODP Expedition 320 Sites U1331-1334). Journal of Nannoplankton Research. 32(2): 3-51. gs O

Bown, P. R. & Newsam, C. (2017). Calcareous nannofossils from the Eocene North Atlantic Ocean (IODP Expedition 342 Sites U1403–1411). Journal of Nannoplankton Research. 37(1): 25-60. gs O

Bralower, T. J. & Mutterlose, J. (1995). Calcareous nannofossil biostratigraphy of Site U865, Allison Guyot, Central Pacific Ocean: a tropical Paleogene reference section. Proceedings of the Ocean Drilling Program, Scientific Results. 143: 31-74. gs

Hay, W. W. & Mohler, H. P. (1967). Calcareous nannoplankton from Early Tertiary rocks at Point Labau, France and Paleocene-Early Eocene correlations. Journal of Paleontology. 41(6): 1505-1541. gs

Perch-Nielsen, K. (1985). Cenozoic calcareous nannofossils. In, Bolli, H. M., Saunders, J. B. & Perch-Nielsen, K. (eds) Plankton Stratigraphy. Cambridge University Press, Cambridge 427-555. gs

Romein, A. J. T. (1979). Lineages in Early Paleogene calcareous nannoplankton. Utrecht Micropaleontological Bulletin. 22: 1-231. gs O

Sullivan, F. R. (1965). Lower Tertiary nannoplankton from the California Coast Ranges. II. Eocene. University of California Publications in Geological Sciences. 53: 1-74. gs O

Varol, O. (1989). Eocene calcareous nannofossils from Sile (northwest Turkey). Revista Española de Micropaleontología. 21: 273-320. gs

Taxa ordered alphabetically (time control age-window is: 0-800Ma)
				robust bars on distal surface define pores which are clearly visible in LM
				Toweius serotinus Medium sized (6-8 µm) with >=10 pores
				Toweius pertusus Small to medium-sized (4-6 µm) with >=10 peforations.
				Toweius tovae Medium to large with 5-9 (frequently 6) large pores
				Toweius eminens Medium sized (typically 6-8 µm) with 4 large pores.
				Toweius occultatus Medium to large with 2 large openings in the central area.
				Finely perforate central plate
				Toweius reticulum Very small (2-3µm); narrowly elliptical; central area wide, spanned by radial bars.
				Toweius selandianus Very small to small (2-4µm); narrowly elliptical; central area narrow, spanned by a net.
				Toweius rotundus Small (~<4 µm); sub-circular to circular; central area narrow, spanned by a plate with perforations too small to resolve in LM.
				Toweius patellus Medium sized; broadly elliptical to sib-circular; central area broad, spanned by a plate with perforations too small to resolve in LM.
				Toweius callosus Medium sized (4-8 µm); elliptical to sub-circular Toweius; central area spanned by a fine proximal net (often missing and not visible in LM)
				Toweius magnicrassus Large to very large (8-15 µm); broadly elliptical to subcircular; central area narrow. Shields are moderately birefringent and tube cycle is highly birefringent.
				Toweius brusselensis
				Central plug
				Toweius gammation Medium sized; circular; central area with bright central plug crossed by strongly curving swastika-like extinction lines. Shield elements are usually conspicuous in LM.
				Unidentified
				Toweius sp. Specimens which cannot be assigned to any established species

Toweius

References:

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