Catalog - Globorotalia nana pseudocontinuosa

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Globorotalia nana pseudocontinuosa

Citation: Globorotalia nana pseudocontinuosa Jenkins 1967

Type specimens: N.Z. Geological Survey Register No. TF 1530: holotype and 3 paratypes

Type age (chronostrat): Otaian Stage: G. woodi connecta zone (Lower Miocene).

Type locality: 2/554, F 14851, grid ref.: 448431. Moderately soft, dark blue-grey, calcareous siltstone from the Parengarenga Harbour section. Collected by G. and A. Scott.

Type repository: Lower Hutt, New Zealand; New Zealand Geological Survey

Test free, low trochospiral, dextrally coiled; equatorial periphery quadrilobate, axial periphery rounded. Wall calcareous,perforate, subhexagonal surface pattern.
Chambers with spherical outline,15 forming the test in nearly 3 whorls, 5 in the first and second whorls and 4 in the final whorl, increasing rapidly in size.
Proloculus diameter approximately 0.01 mm.
Sutures on the spiral and umbilical sides radial, slightly depressed. Umbilicus small. Aperture a relatively high, rounded arch with a distinct rim, interiomarginal, umbilical-extra-umbilical.

The coiling ratio of G. nana pseadocontinuosa in the type sample is 28 dextral to 30 sinistral, and this near random coiling preference is maintained throughout its stratigraphic range. In the type sample G. nana pseudocontinuosa is closely related to the 2 other subspecies: Globorotalia nana nana Bolli and Globorotalia nana semivera (Hornibrook). It differs from G. nana nana in having a high-arched aperture, but both subspecies have 4 chambers in the final whorl and are closely related.
G. nana semivera is distinguished in having 5 chambers in the final whorl.
The ancestor of the group is Globorotalia nana nana which first appeared in the upper part of the Middle Eocene in Trinidad (Bolli, 1957), and in the lower part of the Upper Eocene (Kaiatan Stage) in New Zealand (Jenkins, 1966a). G. nana pseudocontinuosa and G. nana semivera evolved from G. nana nana in the upper part of the Whaingaroan Stage (G. euapertura zone).
G. nana pseudocontinuosa is closely related in general test morphology to Globorotalia mayeri continuosa Blow
and the two taxa were found to be morphologically indistinguishable in an Oligocene-Miocene marine sequence
in south-east Australia (Jenkins, 1960). It was apparent that they were homeomorphs, the Oligocene - Lower
Miocene form, now named G. nana pseudocontinuosa, being genetically unrelated to the Middle Miocene G. mayeri
continuosa, which had evolved from Globorotalia mayeri mayeri Cushman and Ellisor well after the extinction
of G. nana pseudocontinuosa (Jenkins, 1960). The same evolutionary series has been found in the New Zealand
Tertiary (Jenkins, 1966b), and G. nana pseudocontinuosa is shown to be randomly coiled, unlike G. mayeri
continuosa, which is sinistrally coiled.

References:

Jenkins, D. G. (1967). Jenkins, D. G. (1967). Planktonic foraminiferal zones and new taxa from the lower Miocene to the Pleistocene of New Zealand. New Zealand Journal of Geology and Geophysics. 10(4): 1064-1078. New Zealand Journal of Geology and Geophysics. 10(4): 1064-1078. gs

Leckie, R. M., et al. (2018). Leckie, R. M. et al. (2018). Taxonomy, biostratigraphy, and phylogeny of Oligocene and Lower Miocene Paragloborotalia and Parasubbotina. In, Wade, B. S., Olsson, R. K., Pearson, P. N., Huber, B. T. & Berggren, W. A. (eds) Atlas of Oligocene Planktonic Foraminifera. Cushman Foundation for Foraminiferal Research, Special Publication . 46(Chap 5): 125-178. In, Wade, B. S., Olsson, R. K., Pearson, P. N., Huber, B. T. & Berggren, W. A. (eds) Atlas of Oligocene Planktonic Foraminifera. Cushman Foundation for Foraminiferal Research, Special Publication . 46(Chap 5): 125-178. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Globorotalia nana pseudocontinuosa Jenkins 1967

Globorotalia nana pseudocontinuosa

References:

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