Catalog - Globigerina pseudodruryi

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Globigerina pseudodruryi

Citation: Globigerina pseudodruryi Brönnimann & Resig 1971

Type age (chronostrat): Lower Miocene

Type locality: South West Pacific, Ontong Java Plateau or Soloman Rise New Guinea: DSDP Leg 7, Hole 64.1

Type repository: Washington; USNM

The fairly large test is a tightly coiled, in the initial portion bluntly rounded, low trochospire with four chambers, only slightly increasing in size, in the last whorl. The cameral sutures are distinct but shallow, hence the outline of the test as seen in spiral and umbilical views is virtually not lobate. In umbilical view, the chambers of the last whorl, with the exception of the ultimate one, are more or less wedge-shaped, elongate, narrowing, almost pointed toward the shallow umbilicus, and broadly rounded peripherally. The ultimate chamber is subglobular about 215 microns in tangential, and about 100 microns in radial diameter, with a relatively small,high-arched aperture of about 75 microns length and
about 35 microns height, set well in the umbilicus and devoid of any distinct rim or liplike border. The ultimate chamberr spans the three previous chambers of the final whorl in nepenthes-like fashion. Wedge-shaped chambers are well-known in the final whorl of Globigerina druryism, Akers, 1955, as illustrated by Blow (1969, pi. 14, fig. 4) and by Plate 5, Figures 1 and 2 of this paper, and in Globigerina nepenthes nepenthes Todd, 1957 (Blow, 1969, pi. 14, fig. 5; Plate 1, Figure 4 of this paper). The calcareous walls are perforate,and their surfaces are coarsely ornamented with heavy,dull-pointed, basally fused pustules, which on the early chambers of the trochospire almost close the wall pores. The holotype coils to the left.
The scanning micrographs show that the pustules and the interconnecting walls of the polygonal meshwork are composite structures made up of numerous small pustules or "crystallites". The apertural border is imperforate and finely pustulate.

The maximum diameter of the holotype is about 375 microns, its axial height about 275 microns. It is from Zone N. 6 of Hole 64.1 and illustrated by the scanning micrograph of a somewhat oblique apertural view, Plate 7, Figure 1.

Globigerina pseudodruryi, n. sp., is a homeomorph in its general form of Globigerina druryi Akers, but differs from this stratigraphically younger globigerine by its small rimless aperture and the more elongate wedge-shaped form of the early chambers of the last whorl as seen in umbilical view. The holotype of Globigerina druryi, deposited in the collections of the U. S. National Museum, was examined by Bronnimann and found to possess wedge-shaped chambers also, but the apertural face is drawn out in the form of an acutely-edged rather strongly projecting eaves-like plate, which is strongly pustulate.

The maximum diameter of a paratype illustrated by the spiral view, Plate 7, Figure 2, is 350 microns. Globigerina nepenthes nepenthes is regarded as a subspecies of Globigerina druryi by Bandy and Ingle (1970, Plate 1, Figure 5). From the stratigraphic situation as established in Hole 62.1, an evolutionary series
from Globigerina druryi to Globigerina nepenthes would be quite possible. This possible evolutionary series needs further study in stratigraphically successive populations with the help of scanning observations.

The maximum diameter of a paratype illustrated by the spiral view, Plate 7, Figure 2, is 350 microns.Globigerina nepenthes nepenthes is regarded as a subspecies of Globigerina druryi by Bandy and Ingle (1970, Plate 1, Figure 5). From the stratigraphic situation as established in Hole 62.1, an evolutionary series from Globigerina druryi to Globigerina nepenthes would be quite possible. This possible evolutionary series needs further study in stratigraphically successive populations with the help of scanning observations. The stratigraphically older Globigerina pseudodruryi,on the other hand, does not seem to be directly related to Globigerina druryi which, according to Blow (1969,p. 266, fig. 2), extends from Zone N. 11 to Zone N. 14, nor to the Globigerina nepenthes-delicatula group of forms.

References:

Brönnimann, P. & Resig, J. (1971). A Neogene globigerinacean biochronologic time-scale of the southwestern Pacific. Initial Reports of the Deep Sea Drilling Project. 7(2): 1235-1469. gs V O

CATALOG OF ORIGINAL DESCRIPTIONS: Globigerina pseudodruryi Brönnimann & Resig 1971

Globigerina pseudodruryi

References:

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