Catalog - Globigerina dinodensis

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.

Globigerina dinodensis

Citation: Globigerina dinodensis Mukhopadhyay 2003

Type specimens: Plate 4, figures 1-6

Type sample (& lithostrat): sample no. 44, section line II; Lower part of bed f in the Dinod Member

Type age (chronostrat): Early Oligocene

Type locality: About 400 meters southeast of Dinod village, Surat District, Gujarat, India

Test small compact, low trochospiral with gradually increasing subglobular chambers; equatorial outline subquadrangular, very weakly to moderately trilobate; dorsal spire with three whorls; early whorl indistinct, penultimate whorl with five gradually increasing subcircular chambers, last whorl with three markedly increasing large chambers; final chamber largest, semi-circular to subrectangular, covering about half the test size; sutures depressed, septal sutures slightly curved in early part of spire, later nearly straight, radial. Outline subrectangular in side view, dorsal side nearly flat with a weak notch; ventral side umbilico-concave; periphery broadly rounded; apertural face flattened; umbilicus shallow, moderately wide, diameter about 70μm, depth 18μm. Ventral side with three subcircular chambers, radially depressed sutures, almost straight anterior edge and distinctly lobed posterior edge; primary aperture large, subcircular, umbilical, diameter about 30 μm, usually partly or wholly covered by a sparsely perforated thin flap-like structure (cover lamina); on its removal, relict aperture of penultimate chamber may appear within the umbilicus; the cover lamina is concave, fragile and restricted to the apertural area; part of primary aperture is visible through the broken cover lamina; it may also appear as tooth like projections into the primary aperture; small subcircular pits, 2-3, often developed at the suture of the cover lamina; these are impersistent and non-uniform. Sometimes striations may appear around the aperture. Test surface contains perforations and muricae; perforations coarse to medium, almost uniformly distributed; muricae discontinuous, nonperforate, often bifurcate; well developed in last whorl, but not developed in the apertural face and around umbilicus; shell wall three layered, inner and outer layers thin, middle layer thick with fibre-like transverse structures accompanied by grooved pore channels.

longest test diameter 145μm, shortest 99μm, thickness of the test 49μm and the length of last chamber is 70μm.

Etymology: The species is named after Dinod village of the present study area, Surat District, Gujarat, India.

Remarks: With subglobular chambers, large umbilical primary aperture partly or wholly covered by a flap-like lamina and often bordered by subcircular pits, the described species possesses characters both of Catapsydrax Bolli, Loeblich and Tappan, and Globigerina d’Orbigny. The apertural cover lamina resembles the flap-like lip of a Globigerina while the occasional sutural pits bordering the cover lamina are akin to the supplementary apertures of Catapsydrax. However, the weakly concave cover lamina is not a bulla and there occurs no secondary sutural aperture around the cover lamina. Moreover, a muricated surface ornamentation does not occur in a Catapsydrax. The flap–like cover lamina restricted to the apertural area is inconsistent in development, and the pits bordering the cover lamina appear of varying nature. These inconstant and unstable structures appear as temporarily developed on and around the primary aperture and as such have little taxonomic importance. In view of these and considering the overall morphological characters the described species is considered to belong to Globigerina.

Globigerina dinodensis n. sp., a three chambered (in the last whorl) low trochospiral form with last chamber covering about half the test size, a large umbilical aperture and muricate ornamentation, is conspicuous in the P17-P18 transition assemblage. In spite of variations in the aperture, cover lamina, bordering sutural pits and furrows, muricae and peripheral margin the species is morphologically distinct. At times the primary aperture may be concealed by complex laminae. The cover lamina and its sutural pits are temporary structures on and around the aperture. Globigerina sp. a in the e bed (Mukhopadhyay 1997, p. 219, pl.1, fig. 22, pl. 2, figs. 12-14) is a three chambered (last whorl) hispid form having a low open aperture. Globigerina dinodensis n. sp. is distinguished from Globigerina linaperta Finlay in apertural and ornamentation characteristics; the latter has a lipped aperture. Globigerina sellii Borsetti has a low aperture, spinose surface and a distinctly flattened apertural face. Globigerina tripartita tapuriensis Blow and Banner (Blow and Banner 1962, pl. 10, Figs. K, J, and H) is a closely comparable form reported from a similar stratigraphic level of Lindi area of East Africa; however, by possessing a partly visible fourth chamber in the ventral view, a thinly lipped open aperture and nonmuricated surface it is easily distinguished from G. dinodensis n. sp. With an apertural flap-like lip projecting over almost half the width of the umbilicus or sometimes covering almost the whole aperture Globigerina yeguaensis Weinzeri and Applin subsp. pseudovenezuelana Blow and Banner superficially resembles G. dinodensis n. sp. but differs in the peripheral outline and in surface ornamentation; moreover, G. dinodensis n. sp. does not possess a lip. Globigerina dinodensis n. sp. occurs in beds e and f of the study area.

References:

Mukhopadhyay, S. K. (2003). A rare foraminiferal assemblage with new species of Nummulites and Globigerina from the Eocene-Oligocene transition strata of Cambay Basin, India. Micropaleontology. 49: 65-93. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Globigerina dinodensis Mukhopadhyay 2003

Globigerina dinodensis

References:

Add Comment

Comments