Pseudorbitolina Douvillé, 1910

SCHLAGINTWEIT, FELIX, 2023, Annular Chambers In Cretaceous Orbitolinidae (Larger Benthic Foraminifera): An Overview, Acta Palaeontologica Romaniae 19 (1), pp. 45-52 : 50

Genus Pseudorbitolina Douvillé, 1910

Remarks: The taxonomic status of Pseudorbitolina has been treated controversely in the literature: Meandropsinidae ( Henson, 1948) , Soritidae subfamily Meandropsininae ( Loeblich & Tappan, 1964) , Orbitolinidae ( Galloway, 1933, Loeblich & Tappan, 1987: subfamily Dictyoconinae ), Incertae sedis ( Neumann, 1978). One reason for Henson (1948, p. 103) not placing Pseudorbitolina into the Orbitolinidae was the non-alternating main partitions and foramina. These features compare Pseudorbitolina to the Dictyorbitolininae as defined by Schroeder in Schroeder et al. (1990) (Schlagintweit, 2022). As the test construction of annular chambers throughout does not represent an exclusion criterion, Pseudorbitolina is herein assigned to the Dictyorbitolininae thus becoming its second upper Cretaceous representative together with Gusicella Schlagintweit & Rashidi, 2021 ( Fig. 3l, o ).

Pseudorbitolina schroederi Luger, 2018

Fig. 3e, i , j-k, m-n

*2018 Pseudorbitolina schroederi n. sp. – Luger, p. 72, pl. 7, figs. 6-9.

Remarks: Pseudorbitolina schroederi was described by Luger (2018) from the Maastrichtian of Somalia. Other occurrences, sometimes assigned to Pseudorbitolina marthae Douvillé , are from the Maastrichtian of Qatar ( Henson, 1948), SE Turkey ( Meriç, 1974), Iraq ( Radoičić, 1979), and Iran ( Schlagintweit, 2020). Morphologically, P. schroederi is characterized by a convexo-concave test displaying annular-concentric chambers mainly throughout the complete ontogeny ( Figure 3e, i ). As in specimens of Palorbitolinoides hedini ( Figure 2b–c ), axial sections of P. schroederi may show an embryo that is directly followed by annular chambers Fig. 3i ). Henson (1948, p. 102–103) remarked that (1) the apertures of consecutive chambers are in alignment, (2) the radial partitions typically arranged in radial rows and that each layer contains a chamber which is tubular, undivided, completely cyclical. Note that only the ultimate opening of the foraminiferan shell cavity towards the outer ambient environment is termed here tubular aperture, while those inside refer to tubular foramina (see Hottinger, 2006) ( Fig. 3k ). The test structure of Pseudorbitolina has been illustrated by Henson (1948, fig. 16) in several schematic drawings (e.g., Figure 3k, n ), and also clearly evidenced in the thin-section specimens from the upper Maastrichti- an Tarbur Formation ( Fig. 3e, h, k ). In the Upper Cretaceous orbitolinid Gusicella minima (Henson) equivalent aligned tubular foramina, sensu Henson (1948), are present and arranged in a concentric ring at the transition between marginal to central zones (see Schlagintweit & Rashidi, 2021 for details) ( Fig. 3l, o ). As in Pseudorbitolina , the radial main partitions as well as the tubular foramina of Gusicella are arranged in alignment between subsequent chambers. In contrast to Pseudorbitolina , Gusicella additionally has multiple foramina within the pillared central zone. This conical form with uniserial chambers has been assigned to the subfamily Dictyorbitolininae Schroeder in Schroeder et al. (1990) as the first Upper Cretaceous taxon of this group ( Schlagintweit & Rashidi, 2021). The Dictyorbitolininae includes Orbitolinidae that display foramina arranged in a ring at the outer margin of the central zone, with an alignment paralleling the vertical main partitions (beams) (Schroeder in Schroeder et al., 1990, p. 196). They are arranged perpendicular to the septum (verticaux par rapport au plancher = perpendicular to the floor, meaning septum), in continuity paralleling the cone mantel line like in Gusicella and Pseudorbitolina . Although also called ouvertures marginal by Schroeder in Schroeder et al. (1990), they differ from the marginal apertures (and foramina) of the Paleogene taxa where these are arranged obliquely to the septum (i.e., about 45 o with the mantel line of the cone). Following Henson (1948), the marginal foramina of the Dictyorbitolininae should be termed tubular foramina as they are in vertical continuity (= linear arrangement) from one chamber to the next. In the Paleogene forms, they alternate regularly from one chamber to the next one, are laterally displaced to each other, not in linear continuity, but they also form a single circular row as discerned in transverse sections ( Hottinger & Drobne, 1980, p. 211).

Figures

Fig. 3 Annular chambers in Coskinolinella daguini Delmas & Deloffre (upper Aptian Reocín Formation of Spain; a–-c, d?, f), Coskinolinella santanderensis Ramírez del Pozo (early Albian of Spain; g-h), Pseudorbitolina schroederi Luger (upper Maastrichtian Tarbur Formation of Iran; e, i–j, k, m-n: reconstruction of Henson, 1948), and some comparisons with Gusicella minima (Henson) (upper Maastrichtian Tarbur Formation of Iran; l, o). a subaxial section. Note the presence of foramina (left side) of unknown distribution pattern throughout the test. b–c oblique sections. d Drawing of the dorsal side of an isolated specimen with two annular chambers highlighted in colours (modified from Hofker, 1965, fig. 1, without scale, illustrated as C. daguini it might in fact belong to C. santanderensis). e subaxial section. Note the concentric arrangement of foramina (radial tubular apertures sensu Henson, 1948) in line between subsequent chambers in the middle part of the annular chambers (solid red left in the test, dotted red in the reconstructed part). f tangential section; approximate position shown in b (1------2). g-h tangential section showing intercalary beams. i axial section of a megalospheric specimen (em = embryo). j Detail from Fig. 3e (axial section) showing aligned tubular apertures (= tubular foramina, t.f.) sensu Henson (1948). k Schematic drawing modified from Henson (1948, fig. 16a) showing aligned tubular foramina (t.f., arrows towards test base) and primary chambers (p.ch.) in axial section (arrows); t.a. aperture at test base. l Part of the test in axial section showing aligned tubular foramina at the transition marginal to central zone. m–n Tangential sections showing aligned main partitions (m: thin-section, n: reconstruction from Henson, 1948, fig. 16e). o Part of the test in tangential section showing from left to right the cellular subepidermal network, and aligned vertical main partitions and tubular foramina.

Fig. 2 Annular chambers in Palorbitolinoides hedini Cherchi & Schroeder from the middle Albian Kazhdumi Formation of southwestern Iran. a Reflexed conico-concave test (Henson, 1948, fig. 12k–l). Early uniserial post-embryonic chambers marked in orange. b–c Low conico-concave test (Henson, 1948, fig. 12i–j) completely formed by annular post-embryonic chambers, so that the embryo base marks the test base. d High covexo-concave test (Henson, 1948, fig. 12r); compare to the specimen of Pseudorbitolina schroederi Luger shown in Fig. 3d.