Catalog - Globigerina yeguaensis pseudovenezuelana

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Globigerina yeguaensis pseudovenezuelana

Citation: Globigerina yeguaensis subsp. pseudovenezuelana Blow & Banner 1962

Type sample (& lithostrat): sample FCRM 1923

Type locality: LIndi area, Tanzania

"The fairly large test consists of about three whorls of rapidly enlarging, moderately inflated, partially embracing chambers which are coiled in a low trochospire with about four chambers in each whorl. The equatorial profile of the test is subcircular to subquadrate and the equatorial periphery is weakly lobulate. The axial profile of the test is broadly ovoid and the axial periphery is broadly rounded. The chambers are ovate in both ventral and axial views; in dorsal view, the chambers are initially semicircular, but become reniform and distinctly longer than broad during ontogeny. The test, like the later chambers, is depressed and is much more strongly convex ventrally than dorsally. All the sutures are distinctly depressed. The dorsal intercameral sutures meet the strongly lobulate spiral suture almost at right angles; initially they are curved, but become subradial during ontogeny. The ventral umbilicus is moderately broad, open and deep; it is clearly delimited by the steeply sloping apertural faces of the last and penultimate chambers and the umbilical margins of the earlier chambers. The apertural face is narrow, distinctly flattened and is parallel to the axis of coiling, directly facing the umbilicus. The umbilicus isa very low arch, entirely within the umbilicus. The aperture is furnished with a very strongly developed flap-like lip which often projects over almost half the width of the umbilicus. The lip may be broad throughout its length, but it is always distinctly broadest at its mid-point; sometimes the lip is of distinct triangular shape ('umbilical tooth'). Relict apertures, with their umbilical teeth, may be seen within the umbilicus. The wall of the test is fairly thick, moderately coarsely perforate and fairly coarsely hispid. The hispidity is usually strongest around the umbilical margins.

Maximum diameter of holotype 0·51 mm

Globigerina venezuelana Hedberg, Bolli, 1957 (not Hedberg, 1937), Bull. U.S. Nat. Mus . 215, 164, pl. 35, figs. 16a17.

Remarks: This subspecies is distinguished from Globigerina yeguaensis yeguaensis by its slower rate of chamber enlargement, more depressed and appressed chambers, flatter apertural face, deeper umbilicus and less lobulate periphery. Globigerina venezuelana Hedberg very commonly has aborted final chambers which obscure essential specific characters. Such a form was illustrated as the type of G. venezuelana by Hedberg (1937). We have searched through near-topotypic material and have observed specimens with a normal growth rate; such a specimen is here figured for comparison (Fig. 11, xv). It can be seen that G. venezuelana Hedberg differs from G. yeguaensis pseudovenezuelana in possessing a smoother test, more depressed (less rounded) chambers in equatorial profile, less strongly depressed sutures, practically no hispidity, even on the umbilical margins and apertural face, less deeply depressed sutures and narrower, more proximally restricted umbilical teeth. 'G. venezuelana-like' forms are therefore present in the Middle Eocene to Oligocene (G. yeguaensis pseudovenezuelana), are absent in the lowest Aquitanian (G. ampliapertura Zone, where only the form G. ampliapertura euapertura is present which could be confused), are present from the upper part of the Globorotalia opima opima Zone probably to at least the Tortoman (I.e. Globigerina venezuelana itself) and from the Pliocene to Recent (G. conglomerata Schwager, see Banner & Blow, 1960a). All these forms seem to be stable end-forms of independent phylogenetic lineages and closely homeomorph one another. G. conglomerata Schwager (see Banner & Blow, 1960a, p. 7, pl. 2, fig. 3) is close to G. venezuelana Hedberg, differing principally from it in its smaller and more restricted umbilicus; as we have previously stated (foe. cit.) these two forms may be only subspecifically distinct. Through the kindness of Dr E . Gasche (Naturhistorisches Museum, Basel), we have been able to examine the holotype of Globigerina bulloides var. quadripartita Koch, J926. This form was originally described from the middle Tertiary of Borneo. Unfortunately, the holotype is very badly damaged, the ventral side being entirely destroyed; however, as the dorsal side resembles G. yeguaensis pseudovenezuelana, it is figured here (Plate IX Gg), although we consider that the name G. bulloides quadripartita Koch should be considered nomen dubium,. Dr Orville L. Bandy has kindly sent us metatypic specimens of his form Globigerina rotundata var. jacksonensis from the upper part of the Jackson formation, Little Stave Creek, Alabama. These metatypes, like his illustrated holotype, possess peculiarly deformed final chambers which obscure the characters we consider to be of specific importance. Although it is impossible to disprove that G. yeguaensis pseudovenezuelana is conspecific with G. jacksonensis Bandy, we consider that his species is incapable of adequate determination and consequently cannot be used in detailed studies.

Stratigraphical range: In the Lindi area, G. yeguaensis pseudovenezuelana ranges from the Middle Eocene to the top of the Oligocene. In Trinidad, it has been recorded by Bolli (1957 c, pp. 159 and 164) as 'G. venezuelana Hedberg' (part) from the Porticulasphaera mexicana Zone, Navet formation (Middle Eocene), to the top of the Eocene.

References:

Blow, W. H. & Banner, F. T. (1962). The mid-Tertiary (Upper Eocene to Aquitanian) Globigerinaceae. In, Eames, F. E., Banner, F. T., Blow, W. H. & Clarke, W. J. (eds) Fundamentals of mid-Tertiary Stratigraphical Correlation. Cambridge University Press, Cambridge 61-151. gs

Olsson, R. K., Hemleben, C. & Pearson, P. N. (2006b). Taxonomy, biostratigraphy, and phylogeny of Eocene Dentoglobigerina. In, Pearson, P. N., Olsson, R. K., Hemleben, C., Huber, B. T. & Berggren, W. A. (eds) Atlas of Eocene Planktonic Foraminifera. Cushman Foundation for Foraminiferal Research, Special Publication . 41(Chap 13): 401-412. gs O

Pearson, P. N. & Wade, B. S. (2015). Systematic taxonomy of exceptionally well-preserved planktonic foraminifera from the Eocene/Oligocene boundary of Tanzania. Cushman Foundation for Foraminiferal Research, Special Publication. 45: 1-85. gs

Wade, B. S., Pearson, P. N., Olsson, R. K., Fraass, A. J., Leckie, R. M. & Hemleben, C. (2018c). Taxonomy, biostratigraphy, and phylogeny of Oligocene and Lower Miocene Dentoglobigerina and Globoquadrina. 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 11): 331-384. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Globigerina yeguaensis subsp. pseudovenezuelana Blow & Banner 1962

Globigerina yeguaensis pseudovenezuelana

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