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Linked specimens: London, UK; NHM (45554) London, UK; NHM (PM P 45553)
Current identification/main database link: Globotruncana esnehensis Nakkady 1950
Main variation. - Chambers 18-22, arranged in 3-3½ whorls, generally dextrally coiled. The last whorl is composed of 6-7 chambers. In some specimens the partly developed secondary keel is completely reduced leading to forms with a single keel throughout the last whorl.
Original Description
Size:
Extra details from original publication
Remarks. - Globotruncana sharawnaensis is unique among the known Globotruncana species, in as much as it shows a single keel on the early part of the last whorl and a double keel on the last one or two chambers. The tendency to reduce the ventral keel in double-keeled globotruncanas was clearly observed in various sp ecies which normally show a double keel in the early part of the test and become single keeled later (i.e. reduction by palingenesis). However, no species has yet been recorded as having a single keel in the early stage and a double keel later, although reduction of the ventral keel by proterogenesis would produce such forms.
Forms of G. sharawnaensis, with an entirely single keel appear to be somewhat similar to G. conica White. However, G. sharawnaensis is distinguished from G. conica by its slightly smaller test, less conical dorsal side and slightly more protruding ventral one, its somewhat rough ventral side, partially developed ventral keel and acute axial periphery. It differs from G. orientalis El-Naggar in its depressed ventral sutures, the character of its keels and the slightly rougher surface on the ventral side. Globotruncana esnehensis Nakkady and Osman is distinguished from G. sharawnaensis El-Naggar by its dome-shaped test, less protruding and more undulating ventral side, more inflated chambers on the dorsal side, wider umbilicus, smoother surface, and entirely single keel.
Very little is known about the evolutionary history of G. sharawnaensis. However, it may have evolved from G. area (Cushman) [Pulvinulina area 1926] into G. conica White and/or G. esnehensis Nakkady and Osrnan, although no direct evidence was recorded.
Editors' Notes
El-Naggar, Z. R. (1966). Stratigraphy and planktonic foraminifera of the Upper Cretaceous-Lower Tertiary succession in the Esna-Idfu region, Nile Valley, Egypt, U. A. R. Bulletin of the British Museum (Natural History). supplement 2: 1-291. gsReferences:
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Globotruncana sharawnaensis compiled by the pforams@mikrotax project team viewed: 11-2-2025
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