Taxonomy
Original description: Test small, high, its diameter equal to or greater than the height. Chambers arranged in a high, very steep spiral consisting of three whorls. The final whorl consists of three or four spherical chambers differing but little in size. The penultimate and final whorls usually have the same number of chambers, the first whorl often having up to five chambers. Sutures between the chambers of late whorls depressed, straight; those between the chambers of the first whorl weakly depressed, straight or slightly oblique. Aperture umbilical, an elongate slit, or low, crescentic. Wall radiate, thin, moderately porous. Surface matte.
Entries in the Catalog of original descriptions: Globigerina (Conoglobigerina) dagestanica
The original description by Morozova and Moskalenko (1961) mentions a highly variable morphology regarding the number of chambers in the last whorl, height of test and shape of the trochospire. Typically the diameter of the test is about the same as the height, or the test is higher than wide. As seen from the apex (first chambers) upwards to the third and last whorl, the test may be slightly triangular in outline. Up to 5 chambers in the initial (often very small) whorls and 3 to 4 in the final (third whorl) which increases rapidly in width and height; chambers subglobular in shape with straight sutures; the intra-umbilical aperture is a low to medium high symmetrical arch. The 20 or so specimens described by Wernli and Görög (2007) under Globuligerina aff. dagestanica (Morozova) from the Upper Bajocian through Lower Bathonian of the Southern Jura Mountains in France are more triangular in outline and have less globose chambers. More comparative study is warranted to ascertain that G. dagestanica also occurs in France.
Morphology:
In the topotype assemblage from the Khouroukra section, Dagestan, collected by Larisa Glinskikh, Novosibirsk (Gradstein et al., 2017, and LM photographs displayed here), a majority of specimens is also about as high as wide, but higher or wider specimens also occur. The test shape may be quite variable, with many specimens having a rather irregular, deformed test. There are specimens with 3, 3-4 and 4 chambers in the last whorl; aperture is generally a low arch, and rarely a bit higher, and sometimes looped. Apertures have a thickened rim around it, above the umbilicus. A small bulla may be present.
Wall type:
Character matrix
test outline: | Lobate | chamber arrangement: | Trochospiral | edge view: | Spiroconvex | aperture: | Umbilical |
sp chamber shape: | Inflated | coiling axis: | High | periphery: | N/A | aperture border: | Thin lip |
umb chbr shape: | Inflated | umbilicus: | Narrow | periph margin shape: | Broadly rounded | accessory apertures: | None |
spiral sutures: | Moderately depressed | umb depth: | Shallow | wall texture: | Finely pustulose | shell porosity: | Finely Perforate: 1-2.5µm |
umbilical or test sutures: | Moderately depressed | final-whorl chambers: | 3.5-5.5 | N.B. These characters are used for advanced search. N/A - not applicable |
Most likely ancestor: Globuligerina bathoniana - at confidence level 2 (out of 5). Data source: Gradstein et al. 2017 p.263.
Geological Range:
Notes: Late Bajocian through Bathonian, possibly already occurring in Early Bajocian (Wernli and Görög, 1999 and 2000). Given the overlap in test morphology of G. bathoniana and G. dagestanica, it is possible to find dagestanica-type specimens over a wider stratigraphic and geographic range than provided in the literature.
Last occurrence (top): within Bathonian Stage (165.30-168.17Ma, top in Bathonian stage). Data source: Gradstein et al. 2017
First occurrence (base): within Bajocian Stage (168.17-170.90Ma, base in Bajocian stage). Data source: Gradstein et al. 2017
Plot of range and occurrence data:
Gradstein, F. M., Gale, A. S., Kopaevich, L., Waskowska, A., Grigelis, A. & Glinskikh, L. (2017b). The planktonic foraminifera of the Jurassic. Part I: material and taxonomy. Swiss Journal of Palaeontology. 136(2): 187-257. gs O Morozova, V. G. & Moskalenko, T. A. (1961). Планктонные фораминиферы пограничных отложений байосского и батского ярусов Центрального Дагестана (Северо-Восточный Кавказ) [Foraminiferes planctoniques des depots limitrophes du Bajocien et du Bathonien du Daghestan central (Nord-Est du Caucase)]. Voprosyi Mikropaleontologii. 5: 3-30. gs Simmons, M. D., Boudagher-Fadel, M. K., Banner, F. T. & Whittaker, J. E. (1997). The Jurassic Favusellacea, the earliest Globigerina. In, Boudagher-Fadel, M. K., Banner, F. T. & Whittaker, J. E. (eds) The Early Evolutionary History of Planktonic Foraminifera. British Micropalaeontological Society Publication Series . 17-30. gs References:
Globuligerina dagestanica compiled by the pforams@mikrotax project team viewed: 16-9-2024
Short stable page link: https://mikrotax.org/pforams/index.php?id=110060 Go to Archive.is to create a permanent copy of this page - citation notes |
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