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Description: High trochospiral calcareous globigerinid test, small, test diameter ranging from 0.11 to 0.22mm, height usually slightly exceeding maximum diameter, ranging from 0.12 to 0.29 mm; the final chamber (and sometimes the last two chambers) is broken off in virtually all measured specimens so that the height/diameter (H/D) ratio would be greater than 1 : 1. Chambers hemispherical, arranged in a trochospiral coil of two to three whorls. All chambers (except the bulla) visible from the spiral side; only the three chambers of the final whorl visible from the umbilical side. Proloculus diameter 0.020 to 0.027 mm; limits of proloculus difficult to see from exterior in some specimens due to secondary lamination. In some specimens the proloculus projects below the initial whorl and can be measured (Fig. 3: 2, 7, 14). The proloculus is usually surrounded by four to five hemispherical to elongated (in the direction of coiling) chambers in the first whorl, which forms a low trochospire, sometimes only slightly below the level of the proloculus. The sixth chamber usually increases markedly in size relative to earlier chambers (Fig. 3: 2) and marks the start of two later whorls of 3.5 to three chambers that form a much steeper coil. The third whorl (where preserved) always consists of three chambers (Fig. 3: 2, 4–5 (paratypes), Fig. 3: 6 (holotype), Fig. 3: 10 (paratype), Fig. 10: 1). The umbilicus varies in depth and width: either shallow or open to a depth of one whorl, with a central hollow, in specimens for which the three final chambers are coiled in a slightly more open coil (e.g. Fig. 3: 8; Fig. 10: 1, 6, 7). The area outside the aperture is lined with sharp tubercules with curved hook-like ends (Fig. 9: 5; Fig. 10: 9). The final chamber (or more than one) is always broken off, leaving a scar of attachment at the junction of the wall with older chambers, plus the inner lamella forming the lining of the chamber floor. The scar of attachment in some specimens suggests that the final chamber was a thin-walled inflated bulla, terminating the trochospiral coil by covering the central umbilical area and the aperture of the previous chamber (Fig. 3: 1, 9, 10–11). This bulla structure also has a lining of inner lamella covering its floor. No complete bulla has been found. The aperture consists of a medium to high, slightly asymmetrical arch, not semicircular, often sloping backwards up the face of the chamber. The aperture is variable in position, some specimens having it placed centrally on the final (preserved) chamber (Fig. 3: 3, 9, 12), while in others the position is slightly extraumbilical (Fig. 3: 5, 8). Such variations are connected to the tightness of coiling: in some specimens there is an open triangular umbilical hollow, one chamber deep, as a separate space (Fig. 3: 8; Fig. 9: 2, 3; Fig. 10: 1, 6, 7). In other specimens the last three chambers are in close contact so that there is only a shallow depressed area (or the apertural opening) at their junction (Fig. 3: 9, 12). In the tightly coiled specimens the aperture lies close to the centre of the specimen, whilst in the looser coiled, the aperture on the last chamber is naturally more offset towards the outside of the specimen (Fig. 3: 8). The aperture is bordered by a thickened asymmetrical lip (Fig. 3: 1, 5, 8, 9). At the end bordering the umbilicus, the margin of the aperture forms a nearly straight vertical wall connecting with the chamber surface below. Successive apertures rotate at angle of 120◦ around the umbilicus (Fig 3: 5; Fig. 9: 5; Fig. 10: 1). During the construction of the next chamber the apertural lip is extended into a portico-like structure by the deposition of inner lamella forming the floor of the next chamber (Fig. 10: 1),
Wall structure: Each chamber wall is initially bilamellar; all older chambers have additional layers of secondary lamination. The wall consists of (1) perforate inner lamella approximately 1 μm thick, completely covering each chamber including its floor (Fig. 8: 13); (2) outer lamella, perforate and with very low pseudomuricae on the outer surface (Fig. 8: 13); (3) secondary lamination covering the entire exterior surface of the test with each chamber addition (Fig. 8: 11–13). Ultimately all depressions in the surface of the proloculus and earliest chambers are infilled by secondary lamination (Fig. 3: 14). External wall “ornament” of pseudomuricae varies from chamber to chamber as part of the growth of the test, and pseudomuricae progressively increase in size with secondary lamination. It is therefore essential to specify which chamber close-up photographs of surface ornament are from. Ornament in the umbilicus consists of sharp pointed tubercules (Fig. 9: 5; Fig. 10: 7–10). They are present in many specimens in the umbilicus and in front of each aperture (Fig. 10: 1, 5, 7–10). Within newly formed chambers, pseudomuricae are covered by inner lamella, and so are smoothed over with the addition of each subsequent chamber, but are still visible as lumps in the chamber floor (Fig. 6: 4). Most specimens show broken remnants of a thin-walled bulla (Fig. 3: 1, 7, 9).
Wall composition: Raman spectroscopy results on G. bathoniana australiana from the well-preserved sample BMR 95/DR7/8, performed by Aleksey Sadekov of the University of Western Australia, indicate that the wall composition of this species is aragonite, with a high organic content. The methodology of measurement is described in DeCarlo et al. (2019).
Extra details from original publication
Occurrence and age
Dredge samples BMR 95/DR7/8 and BMR 96/DR28/16; early Bajocian based primarily on nannoplankton (see Sect. 3).
Remarks: This form appears to be a subspecies of Globuligerina bathoniana (Pazdrowa). The differences from G. bathoniana s.s. are described as follows. The presence of only three (very rarely, 3.5) chambers in the final whorl, the presence of internal lamellae flooring the chambers, and the mediumto high-arched aperture suggest that this is a distinct subspecies within the wide and variable concept of G. bathoniana as described by Pazdrowa (1969), Hart et al. (2012), and Gradstein et al. (2017a). This subspecies has a height that exceeds the diameter (except where later chambers are broken off). In G. bathoniana australiana the proloculus is surrounded by four, rarely five, chambers, with three to four chambers in the second whorl and three in the third whorl. The third whorl in the Australian form (where preserved) always consists of three chambers (Fig. 3: 1–2, 4–5, 6, 9, 10). Pazdrowa (1969) described G. bathoniana as having three to four chambers in the final whorl; the holotype has four. Only specimens DG-5 and possibly DG-6 (Pazdrowa, 1969, fig. 5a–f, 6) are drawn with three chambers in the final whorl, and there is no indication of whether these are “type” specimens or an extreme variant. The paratypes all have four chambers in the final whorl according to Hart et al. (2012) and Gradstein et al. (2017a). The latter authors state that “Our observations do confirm that G. bathoniana does not have 3 chambers in the last whorl; hence, this might be characteristic to assign specimens to G. dagestanica”. However, the holotype of G. dagestanica “has 4 and not 3 chambers in the last whorl” (Gradstein et al. 2017a). G. dagestanica also has a somewhat triangular shape to the test when seen in outline, whereas G. bathoniana australiana has strongly inflated chambers, deep sutures, and a petaloid outline in umbilical or spiral view (Fig. 3: 2). A clear difference from G. bathoniana s.s. is that all of the Australian specimens have three chambers in the third whorl. If one takes an assemblage view of species (as does Gradstein et al. 2017a), then the geographically remote Australian assemblage has shifted its coiling mode to a three-chambered form and does not have the largely four-chambered coiling of the European form.
The present form is similar to G. bathoniana gigantea Wernli and Görög (1999), in that only three chambers make up the later whorls, but differs from it by being smaller (height 0.11 to 0.28 mm versus 0.28 to 0.32 mm), by having a more conical tapering test shape with strongly inflated chambers and deeper sutures, whereas gigantea has more tightly appressed chambers, and by often having the proloculus prominent in side view, whereas the profile of the base of gigantea is more rounded. Both these subspecies include specimens much larger than G. bathoniana s.s. according to fig. 12 of Pazdrowa (1969), which shows a maximum height of 0.195 mm and a maximum diameter of 0.185 mm.
From the high-spired Globigerina (Conoglobigerina) avarica Morozova 1961, G. bathoniana australiana differs in being much less triangular in outline and in having inflated hemispherical chambers and well-defined sutures. It is felt that these differences justify the erection of this new subspecies, Globuligerina bathoniana australiana.
Comparison of age range Pazdrowa’s specimens of Globuligerina bathoniana s.s. were from the middle Bathonian of Poland, and the species is reported to range from the Bajocian to the Kimmeridgian. This Australian material is very early in the species range (earliest Bajocian). Globuligerina bathoniana gigantea Wernli and Görög is also recorded from the Bajocian.
Globuligerina bathoniana australiana compiled by the pforams@mikrotax project team viewed: 3-12-2022
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