Aulosina oberhauseri ( Koehn−Zaninetti and Brönnimann, 1968 )

Rigaud, Sylvain, Martini, Rossana & Rettori, Roberto, 2013, A new genus of Norian involutinid foraminifers: Its morphological, biostratigraphic, and evolutionary significance, Acta Palaeontologica Polonica 58 (2), pp. 391-405 : 393-398

Aulosina oberhauseri ( Koehn−Zaninetti and Brönnimann, 1968)

Figs. 2–5.

?1966 Triasina hantkeni Majzon ; Salaj et al. 1966: pl. 2: 4b.

?1967 Arenovidalina pragsoides (Oberhauser) ; Salaj et al. 1967: pl. 2: 2b.

1968 Triasina oberhauseri Koehn−Zaninetti and Brönnimann ; Koehn−Zaninetti and Brönnimann 1968: fig. 1.

1969 Triasina oberhauseri Koehn−Zaninetti and Brönnimann ; Koehn−Zaninetti 1969: pls. 10: C–F, 11: A–D.

1970 Triasina oberhauseri Koehn−Zaninetti and Brönnimann ; Brönnimann et al. 1970: pl. 2: 5.

?1970 Triasina oberhauseri Koehn−Zaninetti and Brönnimann ; Brönnimann et al. 1970: pl. 2: 6.

?1970 Involutina sp. ; Brönnimann et al. 1970: pl. 2: 7.

?1972 Involutina ?; Pantić 1972: pl. 5: 7.

1974 Triasina oberhauseri Koehn−Zaninetti and Brönnimann ; Efimova 1974: pl. 6: 16.

?1976 Triasina oberhauseri Koehn−Zaninetti and Brönnimann ; Salaj 1976: pl. 1: 2.

1976 Triasina oberhauseri Koehn−Zaninetti and Brönnimann ; Zaninetti 1976: pls. 14: 23, 15: 1a, b.

1978 Aulotortus pokornyi (Salaj) ; Piller 1978: pl. 11: 2, 3, 6–8.

?1979 Triasina oberhauseri Koehn−Zaninetti and Brönnimann ; Gaździcki et al. 1979: pl. 1: 9.

1980 Triasina hantkeni Majzon ; He 1980: pl. 73: 10.

1983 Aulotortus sp. ; Gaździcki 1983: pl. 33: 14.

?1983 Aulotortus sp. ; Gaździcki and Reid 1983: pl. 2: 1–3.

?1983 Aulotortus gaschei (Koehn−Zaninetti and Brönnimann) ; Gaździcki and Reid 1983: pl. 2: 4–7.

1983 Aulotortus cf. sinuosus Weynschenk ; Gaździcki and Reid 1983: pl. 2: 8.

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1983 Aulotortus sinuosus Weynschenk ; Gaździcki and Reid 1983: pl. 2: 9.

?1983 Triasina oberhauseri Koehn−Zaninetti and Brönnimann ; Gaździcki and Reid 1983: pl. 3: 1, 2.

?1983? Triasina sp. ; Gaździcki and Reid 1983: pl. 3: 3,4.

?1983 Glomospirella ammodiscoides (Rauser−Chernousova) ; Salaj et al. 1983: pl. 1: 14, 15.

?1983 Triasina oberhauseri Koehn−Zaninetti and Brönnimann ; Salaj et al. 1983: pl. 123: 4c.

?1983 Triasina oberhauseri Koehn−Zaninetti and Brönnimann ; Salaj et al. 1983: pl. 126: 1.

1984 Triasina oberhauseri Koehn−Zaninetti and Brönnimann ; Abate et al. 1984: fig. 1.

?1987 Triasina oberhauseri Koehn−Zaninetti and Brönnimann ; Salaj 1987: pl. 2: 4, 5.

1989 Aulotortus sp. ; Matarangas and Skourtis−Coroneou 1989: fig. 4.

?1990 Triasina oberhauseri Koehn−Zaninetti and Brönnimann ; He and Wang 1990: pl. 10: 12, 13.

1990 Triasina oberhauseri Koehn−Zaninetti and Brönnimann ; He and Wang 1990: pl. 10: 14, 15.

?1990 Triasina oberhauseri Koehn−Zaninetti and Brönnimann ; Kristan−Tollmann 1990: pl. 8: 11.

1991 Triasina oberhauseri Koehn−Zaninetti and Brönnimann ; Röhl et al. 1991: pl. 62: 3.

1992 Triasina oberhauseri Koehn−Zaninetti and Brönnimann ; Zaninetti et al. 1992: pls. 1: 3, 4: 1.

?1992 Aulotortus sinuosus pragsoïdes (Oberhauser) ; Zaninetti et al. 1992: pl. 2: 2.

1993 Pilamminella gr. gemerica–kuthani; Peybernès et al. 1993: figs. 13–15.

1994 Triasina oberhauseri Koehn−Zaninetti and Brönnimann ; Villeneuve et al. 1994: pl. 4: 1.

?1994 Aulotortus ex gr. sinuosus Weynschenk ; Villeneuve et al. 1994: pl. 3: 1.

?1994 Aulotortus sp. ; Villeneuve et al. 1994: pl. 4: 2.

?1997 Triasina oberhauseri Koehn−Zaninetti and Brönnimann ; Salaj and M’Zoughi 1997: pl. 9: 2.

2007 Triasina hantkeni Majzon ; Roniewicz et al. 2007: pl. 2: 4.

Holotype: NHMB−C27488 , Koehn−Zaninetti and Brönnimann (1968);

see Fig. 2B herein.

Type locality: Grünau, Almtal, Austria.

Type horizon: Norian Dachstein limestone of the Dolomites.

Diagnosis.— Triasininae presenting a non−overlapping (evolute), mostly sigmoidally coiled tubular chamber regularly constricted by strengthenings.

Description.—The test is free, lenticular with a rounded periphery ( Fig. 4C, I) to slightly biumbilicate ( Fig. 4E, H). A probable polyembryonism has been documented ( Fig. 5J–L ). The test is formed by a globular proloculus with a simple opening ( Fig. 5I ) followed by an enrolled undivided tubular chamber, mostly sigmoidally coiled. Gradually enlarging alongside its 7 to 11 whorls, the tubular chamber, non overlapping (evolute), appears oval in axial section, later possibly becoming kidney−shaped to chevron−shaped against the preceding whorl. Numerous inner strengthenings of the wall regularly constrict both sides of the interior tube from the floor to the roof ( Fig. 4). Reduced in the first whorls ( Fig. 4K, L), these structures increase in size whorl by whorl but never project beyond the half of the tubular chamber lumen. In tangential sections of the tubular chamber, these strengthenings may appear falsely to represent subdivisions into chamberlets or “inner−pillars” (e.g., Fig. 4B, C). Developed on both sides of the tubular chamber, the laminar extensions of the tube wall (lamellae sensu Piller 1978) increase in length whorl by whorl such as in the last whorls, lamellae may laterally interfinger, building umbilical masses ( Fig. 5C–F ).

Among centred−specimens, four distinct morphological groups have been identified:

Morphotype 1 ( Fig. 3A–C): This form shows a compact sigmoidal stage of coiling becoming almost planispiral in 2 to 6 whorls. The number of coils never exceeds 7.5 whorls.

Morphotype 2 ( Fig. 3D–F): With up to 11 whorls, this form has a first compact sigmoidal stage of 3–4 whorls followed by another sigmoidal stage (in inverse order or in another axis of coiling) becoming almost planispiral in 2 to 5 whorls.

Morphotype 3 ( Fig. 3G–I): Form distinct by a first streptospirally coiled stage of 2–3 whorls, possibly with a 90 ° change in coiling direction between whorls, followed by a compact sigmoidal stage becoming almost planispiral in 2 to 5 whorls. The number of coils only rarely exceeds 9 whorls.

Morphotype 4 ( Fig. 3J–L): It presents a first streptospirally coiled stage of 2–3 whorls, possibly with a 90 ° change in coiling direction between whorls, followed by a compact sigmoidal stage of 2–4 whorls and another sigmoidal stage (in inverse order or in another axis of coiling) that becomes almost planispiral in 2 to 4 whorls. The number of coils is about 7–9 whorls.

Some additional irregularities exist: (i) in the morphotype 1, the proloculus is larger than in other morphotypes; (ii) lamellae are more developed in the first whorls of the morphotype 1, other morphotypes are distinguished by lamellae that firstly scarcely cover the test ( Fig. 5G, H ), such as juvenile forms may appear evolute.

F. Paratype, NHMB−C27488 c, thin section 583; oblique, centred section (F 1) and associated reconstituted drawing (F 2). The first stage of coiling is sigmoidal. G . Paratype, NHMB−C27487 b, thin section 582; oblique section. Abbreviations: l, lamella; n. l., narrowed lumina; p, perforation; s, strengthening; u. m., umbilical mass. Scale bars 50 µm .

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Wall calcareous, perforate, commonly recrystallised but probably originally hyalino−radial, fibrous, aragonitic. Several perforations, radially−arranged, riddle the tube wall and the lamellae without ever crossing the internal tube structures ( Fig. 4A). Aperture simple, terminal (open end of the tubular chamber).

Dimensions.—Specimens of Aulosina oberhauseri from the Black Marble Quarry vary in size from 100 to 300 µm in diameter and 75 to 150 µm in height, the largest being adult forms. The proloculus is globular with a diameter ranging from 20 to 38 µm (20 to 26 µm in the morphotypes 2, 3, 4 and 24 to 38 µm in the morphotype 1). The tubular chamber and associated lamellae gradually increase in size. Lumen of the first stage being generally from 4 to 8 µm in height whereas lumen of the last whorls reach up to 28 µm. Wall perforations are about 2–4 µm in diameter. The strengthenings thicken the tubular chamber wall on a length of 1–2 µm in the first whorls and up to 30 µm in the last whorls. Their thickness is proportional and never exceeds 14 µm.

The documented Tethyan specimens of Aulosina oberhauseri vary in size from 265 to 600 µm in diameter (the 1 mm specimen illustrated by Salaj and M’Zoughi 1997, strongly recrystallised, is here considered to be doubtful). Forms of the original material are, on average, 400 µm in diameter ( Koehn−Zaninetti and Brönnimann 1968). However, involutinids of the Black Marble Quarry apparently represent a dwarfed fauna. Small sizes are observed for representatives of the genera Auloconus , Aulosina , Aulotortus , Frentzenella , Licispirella , Parvalamella , and Trocholina . Moreover, juvenile forms are rarely illustrated in the literature.

Microfacies and palaeoecology.—The dark grey to black limestone beds of the Black Marble Quarry are mostly composed by muddy microfacies (mudstone, wackestone and packstone) typical of a quiet, periodically restricted, shallow−water lagoonal environment ( Rigaud 2012). In some beds small corals or sponge thickets occur.

Foraminiferal association.— Aulosina oberhauseri is found in association with representatives of the Family Involutinidae ( Auloconus , Aulotortus , Frentzenella ,? Lamelliconus , Licispirella , Parvalamella , Trocholina and Wallowaconus ), Duostominidae ( Cassianopapillaria , Variostoma ), Oberhauserellidae ( Praegubkinella , Oberhauserella , Schmidita ), Polymorphinidae ( Eoguttulina , Guttulina ), Trochamminidae ( Trochammina ), Endothyridae , Ophthalmidiidae ( Gsollbergella ) and indeterminate lagenids, miliolids and?lituolids.

Remarks.—In the original systematic description of Aulosina oberhauseri, Koehn−Zaninetti and Brönnimann (1968) described: (i) pillars limited to the periphery of the tubular chamber; (ii) embracing lumen in the adult stage; (iii) convex, protuberant umbilical masses. These traits have not been observed in sections of specimens from the Black Marble Quarry and the revision of the original material leads us to reconsider these observations: (i) in opposition to pillars, the internal tube structures of A. oberhauseri only laterally thicken the tube wall such that they are justifiably limited to the periphery of the lumen ( Fig. 4B–J); (ii) like in Aulotortus , the tubular chamber of A. oberhauseri is only gradually enlarged so that in section, the lumen are laterally restricted (evolute or non−overlapping tubular chamber). The described embracing lumen are in fact morphological misinterpretations related to oblique sections ( Fig. 4D); (iii) the diagenetic result subsequent to the recrystallisation, dissolution or micritisation of the test periphery, sometimes gives the erroneous impression that the umbilical masses are protuberant ( Figs. 2B, 5F, I ). For example, in the holotype, partly micritised, a part of the test periphery is lacking suggesting that its umbilical masses are protuberant ( Fig. 2B 1) but remnants of its perforations reveal an initial lenticular geometry ( Fig. 2B 2).

Despite the fact that majority of the illustrated Tethyan specimens have a larger size, their shape and innermost structure fit in every respect with specimens from the Black Marble Quarry (e.g., Fig. 2C). In the original material, the discovery of paratypes in which the first stage of coiling and the proloculus are preserved ( Fig. 2D, F) reveals that the coiling arrangement is equally similar (e.g., sigmoidal coiling in Fig. 2F). In the literature, most illustrations of A. oberhauseri lack the juvenile part (non−centred or recrystallised specimens). Since the last whorls of the species are almost planispiral, it is understandable that the form was first thought to be planispirally coiled.

Aulosina oberhauseri differs from Triasina hantkeni by its reduced size, a more lenticular shape, a non overlapping (evolute) tubular chamber, different kind of internal tube structures (strengthenings instead of internal pillars), wider umbilical masses and probably a more complicated coiling arrangement (the juvenile coiling of T. hantkeni is still unknown). In equatorial and sub−equatorial sections, slightly tangential to the tube lumen, A. oberhauseri strongly resembles T. hantkeni ( Figs. 2C, 3H). The only criteria discerning the two species are the lumen shape of the initial stage and, if the juvenile part is not preserved, the sigmoidal coiling of the last whorls; both pieces of evidence being based on the dissimilarity existing in the tubular chamber lateral overlapping of the two species. In other sections, the observation of inner−pillars in tangential sections of T. hantkeni (never ob−

(arrowhead). H. MHNG 2011−1−440i, equatorial section. I. MHNG 2011−1−440j, slightly oblique section. J–L. Morphotype 4. J. MHNG 2011−1−440k, axial section. K. MHNG 2011−1−440l, sub−equatorial section. L. MHNG 2011− 1−440m, slightly oblique section. Abbreviations: l, lamella; p, perforation; s, strengthening; n. l., narrowed lumen; u. m., umbilical mass. Scale bars 50 µm.

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served in A. oberhauseri sections; Fig. 5A, B ) hampers any confusion.

The species A. oberhauseri differs from representatives of the genus Aulotortus by its coiling arrangement, the shortened lateral extension of its lamellae in the juvenile stage and the occurrence of strengthenings constricting its tubular chamber. In axial, sub−axial to oblique sections, strengthenings are almost not discernible so that the specimens resemble Aulotortus sinuosus ( Figs. 3A, 4L, 5D ) or Parvalamella friedli ( Fig. 3C, F) in which gentle tube undulations may falsely appear to represent strengthenings. In such peculiar sections, the coiling arrangement and the narrowed lumen ( Fig. 5C, H ) are the only features allowing the recognition of A. oberhauseri .

Comments on morphotypes.—The investigated material of Aulosina oberhauseri revealed the presence of four morphotypes. These forms differ in the coiling arrangement, the proloculus size, the lamellae lateral overlapping and the number of coils. All these features are easily identifiable in centred sections.

All morphological groups show a similar stratigraphic and palaeoenvironmental distribution along the Black Marble Quarry succession and display no evolution or variability between their first and last occurrences. Pending further investigations of morphotype distribution in other areas of the world, we refrain to argue that these forms express sexual polymorphism, intraspecific variability, environmental stress peculiar to the Black Marble Quarry depositional environment or even the existence of two or more distinct species.

Nevertheless, the absence of the first stage of coiling in the morphotype 1, its larger proloculus and lower number of whorls combined with its relative abundance, may suggest that this morphotype corresponds to a megalospheric or A form ( Fig. 3A–C). As the measured size of the proloculus strongly depends on the section orientation, the resulting values should be treated with utmost care. We assume, however, that owing to the large number of studied individuals and the fact that the half size of the proloculus does not exceed the thickness of our thin sections (30–35 µm) the measured differences are significant. The microspheric or B form, known to show a more varied morphology ( Loeblich and Tappan 1964), would correspond to one or more of the other identified morphotypes ( Fig. 3D–L). Dimorphism is well known in the Involutinina . It has been, for example, described in Aulotortus ( Koehn−Zaninetti 1969) and Involutina (Gaździcki 1983) .

Geographic and stratigraphic range. —Cosmopolitan in the Tethys and in American Panthalassan terranes of Oregon (this study) and the Yukon ( Gaździcki and Reid 1983). In the Tethyan domain, Aulosina oberhauseri is referred to the Norian–early Rhaetian. In Oregon, the species occurs within the first 48 metres of the Black Marble Quarry, part of the Martin Bridge Formation, late Carnian? to early–middle? Norian in age.

Figures

Fig. 5. Involutinid foraminifer Aulosina oberhauseri (Koehn−Zaninetti and Brönnimann, 1968), Black Marble Quarry (upper Carnian?–lower–middle? Norian). A, B. Tangential sections, MHNG 2011−1−440w (A) and MHNG 2011−1−341c (B). Note the absence of transversely sectioned inner−pillars. C–F. Lamellae interfingering in the umbilical region (white arrowheads). C. MHNG 2011−1−440x, sub−axial; centred section. D. MHNG 2011−1−391a, thin +