Dictyoconinae Schubert, 1912

SCHLAGINTWEIT, FELIX, 2023, Annular Chambers In Cretaceous Orbitolinidae (Larger Benthic Foraminifera): An Overview, Acta Palaeontologica Romaniae 19 (1), pp. 45-52 : 47-49

Subfamily Dictyoconinae Schubert, 1912

Remarks: Due to the simplicity of the embryo (see Hofker, 1965 for details), Coskinolinella is herein includ- ed within the Dictyoconinae .

Genus Coskinolinella Delmas & Deloffre, 1961

Coskinolinella daguini Delmas & Deloffre, 1961

Fig. 3 a-d, f

*1961 Coskinolinella daguini n. gen., n. sp. – Delmas & Deloffre, p. 167, text-fig. 1, pl. 1, figs. 1-8.

Coskinolinella santanderensis Ramírez del Pozo,

*1971 Coskinolinella santanderensis n. sp. – Ramírez del Pozo, p. 254, pl. 62, fig. 1.

Fig. 3 g-h

Remarks: The type-species Coskinolinella daguini was described by Delmas & Deloffre (1961) from upper Aptian-lower Albian carbonates recovered from subsurface drillings performed in the Aquitaine Basin of southwestern France and assigned with hesitation to the Orbitolinidae ( Figure 3a–c, e ). Based on isolated specimens and oriented thin-sections, Hofker (1965) provided the following test morphology: Following a flat initial spire of about two whorls, there are a few discoidal chambers that cover the lower part of the spire which in turn are followed by annular chambers that make up the main part of the test (see Hofker, 1965 for clear details and illustrations). Cherchi (1985) indicated up to 15 to 20 annular chambers in C. daguini . The gross outer test morphology of Coskinolinella is low conical and may display a wavy profile of the test surface making the observation of the continuity of a single chamber extremely difficult ( Fig. 3a ). Such morphotypes have been related to microspheric specimens by Cherchi (1985). It is worth mentioning that such uneven morphologies are also reported from the modern Cycloclypeus , a rotaliid with annular neancic chambers, in cases related to test teratologies ( Briguglio et al., 2016, e.g. Appendix 1).

The marginal part of the chamber may show different degrees of subdivisions allowing for the distinction of three different species. C. daguini (radial main partitions, Fig. 3f ), C. santanderensis Ramírez del Pozo, 1971 (radial main + intercalary partitions, Fig. 3g ) and C. navarrensis Ramírez del Pozo, 1971 (radial main + intercalary partitions + horizontal partitions) that form a lineage with increasing test complexity in the late Aptian-late Albian interval with overlapping species ranges ( Cherchi, 1984, 1985). The radial main partitions are well visible in the type specimens (e.g., Delmas & Deloffre, 1961, fig. 1.6- 7, pl. 1, fig. 8). In the Treatise on Invertebrate Paleontology, Loeblich & Tappan (1964) included Coskinolinella into the family Dicyclinidae with a discoidal or depressed conical test displaying cyclical chambers and furthermore into the subfamily Dicyclininae including, i.e. taxa with chambers partially subdivided by radial transverse partitions. Later, Loeblich & Tappan (1987, p. 697) treated Coskinolinella as a genus of uncertain status and disagreed again with the placement within the Orbitolinidae due to the absence of any internal chamber subdivisions. Loeblich & Tappan (1987) only referred to the work of Delmas & Deloffre (1961) and omitted the wellillustrated works of Hofker (1965) and Cherchi (1984, 1985). It is worth to mention, that the two-layered wall observed from several orbitolinids ( Douglass, 1960; Hofker, 1966; Cherchi & Schroeder, 1978; Cruz-Abad, 2018) has also been observed in Coskinolinella santanderensis ( Fig. 3h ). According to Douglass (1960, p. 252), the outer layer consists of hyaline calcite with variable amounts of silica grains. In the recent classifications of Kaminski (2004, 2014), Coskinolinella is also excluded, obviously following Loeblich & Tappan (1987). Recently, Tasli & Solak (2019) assigned the species Heterocoskinolina bariensis Luperto-Sinni & Reina, 1992 to the genus Coskinolinella based on rich material from the late Albian of Turkey. The adult chamber arrangement was considered as annular ( Tasli & Solak, 2019, fig. 3B) and the internal structure as identical to Coskinolina Delmas & Deloffre. Therefore , the new combination C. bariensis (Luperto-Sini & Reina) was introduced as a fourth species of the genus. The taxonomic revision of Tasli & Solak (2019) is rejected herein, instead classifying the chambers of Heterocoskinolina bariensis as a succession of rectilinear conical chambers (stacked-cone structure) and not being ring-shaped ( Figure 4a ). The axial section shown Fig. 6.1c of Tasli & Solak (2019) shows that the chambers are not annular but are rectilinear (stacked-cones) with the septa pierced by multiple foramina in the central test part referred to as perforated plates ( Figure 4b–c ).

The irregular appearance of the central zone results from the infoldings of the septa (cupules) that converge towards the test axis. Transverse sections near the test base may appear as being annular due to a central concave depression in some specimens ( Tasli & Solak, 2019, figs. 5.1c, 5.3e, 8.4b). Apart from the different interpretation of the test structure, there are also phylogenetic and palaeobiogeographical aspects that would make the occurrence in the Turkish Taurides very surprising. These aspects however were not discussed by Tasli & Solak (2019). The occurrence of a form without rafters ( H. bariensis ) would contradict the Coskinolinella lineage with the late Albian C. navarrensis (with rafters) as end member as established by Cherchi (1984, 1985). It is also noteworthy that the occurrences of Coskinolinella give evidence for a palaeogeographical restricted distribution in the western Neotethys such that any occurrences in its central part and on the southern margin would be surprising. For example, Ghanem & Kuss (2013) reported Coskinolinella from the Albian of Syria. The specimen illustrated in Fig.11.10 as C. navarensis represents a trochospiral form with open umbilicus ( Trochospira ? sp.). The other specimen illustrated as C. cf. santanderensis (Fig. 11.21 therein) is undiagnostic (undeterminable tangential section of any larger benthic foraminifera). Also, the illustrations of Arnaud-Vanneau & Premoli Silva (1995) from the Albian of the Central Pacific (pl. 4, fig. 6: C. daguini , pl. 4, fig. 7: C. navarensis ) are by no means convincing and appear undeterminable not even to genus level. In conclusion, the overall test construction with its prominent stage of annular chambers as well as the coiled initial part would, in my opinion, include the Coskinolinella within the Orbitolinidae , thus confirming the view of Cherchi (1984, 1985).

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. 4 a Schematic reconstruction of Heterocoskinolina bariensis Luperto-Sinni & Reina displaying stocked-cone structure of three chambers with septal infoldings (cupules = cu) converging towards the central area with cribrate foramina (fo). b–c Axial sections re-illustrated from Tasli & Solak (2019, figs. 8.4c and 6.1c, modified), late Albian of Turkey. Abbreviations: fo = foramen, se = septum.