Catalog - Gorbachikella

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Gorbachikella

Citation: Gorbachikella Banner & Desai 1988

Type species: Globigerina kugleri Bolli, 1959

Test trochospiral, consisting of two or more whorls, initially with four or more chambers per whorl, and final whorl of four chambers, which are typically subglobular or reniform; spiral side completely evolute, umbilical side almost completely involute but with a distinct, true umbilicus; aperture intraumbilical, a low or high symmetrical arch; wall calcareous, microperforate (external diameters < 1.5µm), smooth, not muricate, probably calcitic.

Remarks. Gorbachikella closely resembles Globigerina but its wall is smooth and microperforate. It differs from Tenuitellinata in lacking the crystallite pustules characteristic of the Tenuitellinae. Unlike Globuligerina, Gorbachikella has no muricae and it has a symmetrical simple aperture. Gorbachikella differs from Conoglobigerina in lacking muricae, and it differs from Favusella in its lack of a reticulum of anastomosing ridges. The true umbilicus of Gorbachikella places this genus in the Globigerinacea and distinguishes it from Gubkinella.

The phylogenetic origin of Gorbachikella is not known. It is unlikely that muricate Globuligerina, with its specialised aperture, could directly give rise to the smooth, unspecialised Gorbachikella. An origin even with Conoglobigerina (muricate but with a simple arched aperture) would also involve a loss of muricae and (from the work of Gorbachik and Kuznetsova, 1986) a change in the mineralogy of the wall from aragonite to calcite.

A Late Jurassic species referrable to Gorbachikella appears to be G. parva (Kuznetsova) (in Kuznetsova and Gorbachik, 1985, p. 113, pl. 16, figs. 1-2), from the Early Kimmeridgian of the Crimea. The wall appears to be typical, and the aperture is figured as low but intraumbilical.

“Globuligerina” meganomica Kuznetsova (in Kuznetsova and Uspenskaya, 1980, p. 749, pl. 1, figs. 5-8) (re-illustrated by Kuznetsova and Gorbachik, 1985, p. 113, pl. 16, figs. 7-8, and by Gorbachik, 1986, pl. 5, figs. 1-2), from the Early and Middle Callovian of the Crimea, is the stratigraphically oldest known species to be adequately illustrated and which is probably referable to Gorbachikella. None of the specimens so far imaged in SEM has a very well preserved wall, but no evidence for the existence of muricae in this species has yet been presented. Its aperture has been indicated (opera. cit.) as a low arch one which is atypically low for Gorbachikella, but which is not that of Globuligerina. SEM study of better specimens is necessary before the reference of “G.” meganomica to Gorbachikella rather than to Conoglobigerina is certain; it may be that this species is close to an origin of Gorbachikella from Conoglobigerina.

The youngest, firmly dated specimens of Gorbachikella are those which were obtained by Longoria (1974, pl. 11, fig. 14-16) from the Leupoldina cabri zone of the La Peria Formation, northern Mexico. These specimens were incorrectly called “Caucasella hauterivica (Subbotina)” by Longoria (1974, p. 48-49); they lack the surface reticulum of Favusella hoterivica (Subbotina) and should correctly be identified as Gorbachikella kugleri (Bolli) (Plate 2, figs. 1, 2). “Globigerina” kugleri (Bolli, 1959, p. 270, pl. 23, figs, 3-5) was originally described from the Cuche Formation of Trinidad and was believed by Bolli (cit.) to range from the Barremian Toco Formation to the Late Aptian Upper Cuche.

Gorbachikella, with its probable range from Early Callovian to Aptian, is believed to be the direct ancestor of Praehedbergella, because the only morphological change required is an extension of the aperture to a point beyond the limits of the umbilicus.

References:

Banner, F. T. & Desai, D. (1988). A review and revision of the Jurassic-Early Cretaceous Globigerinina,with especial reference to the Aptian assemblages of Speeton (North Yorkshire, England). Journal of Micropalaeontology. 7: 143-185. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Gorbachikella Banner & Desai 1988

Gorbachikella

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			Gorbachikella anteroapertura BouDagher-Fadel, Banner, Brown, Simmons, Gorbachik 1995
			Gorbachikella depressa BouDagher-Fadel, Banner, Brown, Simmons, Gorbachik 1995 = Gorbachikella depressa
			Gorbachikella grandiapertura Bou-Dagher-Fadel, Banner, Brown, Simmons, Gorbachik 1995 = Gorbachikella grandiapertura