Catalog - Globotruncana sharawnaensis Catalog - Globotruncana sharawnaensis

CATALOG OF ORIGINAL DESCRIPTIONS: Globotruncana sharawnaensis El-Naggar 1966

This page provides data from the catalog of type descriptions. The catalog is sorted alphabetically. Use the current identification link to go back to the main database.


Higher levels: pf_cat -> G -> Globotruncana -> Globotruncana sharawnaensis
Other pages this level: << < G. putahensis, G. qabeliatensis, G. quadrata, G. renzi, G. repanda, G. riojai, G. roddai, G. rosetta insignis, G. rosetta pettersi, G. rugosa, G. rugosa subrugosa, G. sahakianae, G. samuriensis, G. schneegansi, G. semsalensis, G. sharawnaensis, G. sigmoconcavata, G. smithi, G. stephani, G. stephani turbinata, G. stephensoni, G. stuarti parva, G. sudrensis, G. sudrensis parallela, G. tarfayaensis, G. thalmanni thalmanni, G. ticinensis, G. torensis, G. tricarinata colombiana, G. tricarinata desioi, G. undulata> >>

Globotruncana sharawnaensis

Citation: Globotruncana sharawnaensis El-Naggar 1966
Taxonomic rank: species
Type specimens: holotype (fig. 3a-d) P.45553; unfigured paratypes, P.45554.
Type sample (& lithostrat): upper Sharawna Shale.
Type age (chronostrat): Upper Cretaceous, Maestrichtian. Common in the Globotruneana gansseri Zone (Middle Maestrichtian), and dies out in the basal part of the overlying G. esnehensis Zone (Upper Maestrichtian).
Type locality: Holotype (fig. 3a-d) and unfigured paratypes from approximately 87.3 meters above the base of the Wadi El-Sharawna section (25° 14'N 32°44'E), about 19 km. southeast of the Nile at Esna, Esna-ldfu region, upper Egypt.
Type repository: London, UK; NHM

Linked specimens: London, UK; NHM (45554) London, UK; NHM (PM P 45553)

Current identification/main database link: Globotruncana esnehensis Nakkady 1950


Original Description

Test large, coiled in a high trochospire; dorsal side broadly convex and highly arched, ventral side almost flat, very slightly raised and weakly inflated; equatorial periphery subcircular, slightly lobate, with a single, well developed, beaded keel on the early chambers of the last whorl and two distinct, closely spaced, beaded keels on the last chamber; axial periphery angular in the early part, truncate on the last chamber, where the two marginal keels are very close and enclose a very narrow peripheral band; chambers on the dorsal side 21, arranged in 3 dextrally coiled whorls and increase slowly in size; the initial chambers are small, inflated, globigerine, and are followed by roughly quadrangular to crescentic chambers; the last whorl is composed of 6.5, large chambers, which are generally crescentic to quadrilateral; on the ventral side the chambers are 6.5, roughly ovoid to somewhat quadrangular, weakly inflated, slightly overlapping, and increase slowly in size; sutures on the dorsal side are curved, raised and beaded in the early part and short, very slightly curved to almost straight, raised and beaded in the later; on the ventral side the sutures are almost straight, radial and depressed in the early part, slightly curved forward and depressed later; umbilicus polygonal in outline, wide, deep, surrounded by slightly raised, delicately beaded ridges and covered by complex, tegilla of which remnants are still preserved; primary apertures interiomarginal, umbilical; tegilla with accessory apertures only poorly preserved; wall calcareous perforate except for the imperforate keels, peripheral band and tegilla; surface smooth on the dorsal side, papillose on the ventral, with the papillae fading out gradually on the last two chambers.

Size:
Maximum diameter 0.50 mm.; minimum diameter 0.40 mm.; thickness 0.28 mm

Extra details from original publication

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.

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
content migrated from chronos

References:

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. gs


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Globotruncana sharawnaensis compiled by the pforams@mikrotax project team viewed: 11-2-2025

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