Orbitolites concava, Bidgood & Schlagintweit & Simmons, 2024

Bidgood, Michael, Schlagintweit, Felix & Simmons, Michael, 2024, The Genus Orbitolina D’Orbigny, 1850 (Larger Benthic Foraminifera) And Its Constituent Species: Notes On Identity And Stratigraphic Ranges, Acta Palaeontologica Romaniae 20 (2), pp. 33-59 : 37-39

Orbitolina concava ( Lamarck, 1816)

Non 1801 Orbitolites concava n. sp. – Lamarck, p. 376 T 1816 Orbulites concava n. sp. – Lamarck, p. 197. Early Cenomanian, France.

1837 Orbitolites plana n. sp. – d’Archiac, p. 178. Cenomanian, France.

Non 1890 Orbitolina concava - Martin, p. 211-219, pl. XXIV, fig. 1-13, pl. XXV, fig. 14-20 (= Palorbitolina lenticularis fide Schlagintweit & Simmons, 2023 )

1960a Orbitolina concava – Douglass, p. 32-34; pl. 2, fig. 1-12; pl. 3, fig. 1-9. Early Cenomanian, France.

1960b Orbitolina concava - Douglass, pl. 2, fig. 6-7; pl. 4, fig. 12-13. Early Cenomanian, France.

1962 Orbitolina (Orbitolina) concava concava – Schroeder, p. 185-189, pl. 20, fig. 3-6, 8-10; pl. 21, fig. 6. Early Cenomanian, France.

1963 Orbitolina lenticularis (Blumenbach) – Hofker jr., text fig. 24; pl. 17, fig. 15-18; pl. 18, fig. 1-9. Early Cenomanian, France.

Non 1964 Orbitolina (O.) concava concava – Schroeder, p. 688-690; text-fig. 3a-d (= Orbitolina duranddelgai fide Schroeder in Schroeder & Neumann, 1985).

Non 1969 – Orbitolina concava – Sampò, pl. 37, fig. 8 (= Palorbitolina lenticularis ), pl. 39, fig. 10, 22 (= Mesorbitolina birmanica ).

1970 Orbitolina concava – Chernov, p. 30-31, pl. 2, figs. 1-9. Early Cenomanian, Ukrainian Carpathians.

Non 1972 Orbitolina (Orbitolina) concava concava – Ramirez del Pozo, p. 36, pl. 4, fig. 8-9 (= Mesorbitolina sp. )

Non 1976 Orbitolina concava – Ho et al., p. 20, pl. 3, fig. 5-11. (= Palorbitolina ultima or Palorbitolinoides fide Rao et al., 2017 ).

1979 Orbitolina (Orbitolina) concava – Decrouez & Kunzle, pl. 1, fig. 1, 4; pl. 2, fig. 1-3 – Early Cenomanian, France.

Non 1982 Orbitolina (Orbitolina) concava – Zhang, p. 75, pl. 12, fig. 8-9. Probably Palorbitolinoides sp.

1984 Orbitolina (Orbitolina) concava – Bilotte, p. 363- 364, pl. 3, fig. 12-14. Middle Cenomanian, French Pyrenees.

1985 Orbitolina (Orbitolina) concava -Schroeder in Schroeder & Neumann, p. 62-66, pl. 29, fig. 1-8 Early Cenomanian, France.

1992 Orbitolina concava – Simmons & Williams, pl. 2, fig. 2. Early Cenomanian, France.

Non 1992 Orbitolina concava – Kalantari, pl. 78, text-fig. 158 (= Mesorbitolina sp. )

Diagnostic features: An Orbitolina with a relatively large embryonic apparatus (min 0.67mm, max 1.21mm, mean 0.85mm) and an irregularly elliptical proloculus (min 0.17mm, max 0.42mm, mean 0.27mm). Supra-embryonic zone divided by numerous vertical partitions of different lengths (orders). Sub-embryonic zone thin, a layer of numerous, irregular chambers. Radial zone chamber passages with an irregular rectangular-oval outline, with septulae alternating between chambers.

Remarks: Orbitolina concava (= Orbulites concava Lamarck, 1816 ) is the type species of Orbitolina ( Schroeder & Simmons, 1988, 1989). First described over 200 years ago, it has had a complex history of usage. In the 19 th century and the first half of the 20 th century, as much attention was paid to the external morphology as to the internal morphology of the orbitolinids, leading to the use of species names that would not be deemed appropriate today, as taxonomic classification is now based on internal features almost exclusively ( Henson, 1948; Douglass, 1960a, 1960b; Schroeder, 1962, 1963, 1975) (see Appendix). Consequently, taxa such as O. concava have many potential synonyms ( Schroeder, 1962).

An understanding of the stratigraphic range of O. concava is hampered by how the species name is being used – in a strict sense as used herein (sensu Schroeder, 1962); in a loose sense possibly including related Orbitolina (sensu lato) species, most of which were originally defined as varieties or subspecies of O. concava ; or in the (incorrect) widest possible sense including a range of Orbitolininae . Some records, especially from the Aptian, Albian, and late Cenomanian of the Middle East, are clear misidentifications, unproven, or relate to outdated concepts of the species (see examples in Schlagintweit & Simmons, 2022 and also Bozorgnia & Banafti, 1964; Sampò, 1969; Kalantari, 1976, 1992; Rabu, 1993). Use of outdated species concepts also applies to records from Borneo ( Schlagintweit & Simmons, 2023). Resolution of such taxonomic uncertainty requires detailed assessment of records that is beyond the scope of this study, although we have attempted to verify the most important range defining records.

Orbitolina birmanica Sahni 1937 emend. Sahni & Sastri 1957 was tentatively considered a synonym of O. concava by Schroeder (1962) but has subsequently been shown to be a species of Mesorbitolina ( Zhang, 1994; Schlagintweit & Wilmsen, 2014; Schlagintweit, 2024). Ho et al. (1976), Yang et al. (1982), and Zhang (1982) reported O. concava as occurring in the Cenomanian of Tibet, but the material is considered to be of the Palorbitolina ultima - Palorbitolinoides hedini lineage by Rao et al. (2017) and thus pre-Cenomanian ( Schroeder et al., 2010).

Measurements made by us on the embryonic apparatuses of scaled illustrations of topotypes of O. concava or from data from Douglass (1960a), Schroeder (1962), Hofker (1963), Decrouez & Kundle (1979), Schroeder & Neumann (1985) and Simmons & Williams (1992) yielded the range of values shown in the diagnosis. It was noticed that Schroeder’s measurements in 1962 were close to those of Hofker’s (1963). However, later measurements by Schroeder (in Schroeder & Neumann, 1985) appeared to be 20-25% larger and, in some respects, closer to those of Douglass (1960a). This (apparent) discrepancy may be connected with issues surrounding image scaling during publication and subsequent re-measurement as discussed above. It could also reflect a genuine wide range of values. Regardless of this and considering the mean values, O. concava is still generally characterised as the species of Orbitolina with the largest embryonic apparatus diameter.

Stratigraphic range: Early – middle Cenomanian (common records in the early Cenomanian, scarce records in the middle Cenomanian). First described from early Cenomanian sediments in Ballon, France ( Lamarck, 1816), Schroeder in Schroeder & Neumann (1985) regarded the range of O. concava as being restricted to the entirety of the early Cenomanian (see range chart therein - a comment (p. 65) that it is “Cénomanien supérieur” is a lapsus calami). They reported no records outside of the early Cenomanian (with ammonite support) of France. This was followed by Simmons & Bidgood (2023). Its inception is considered as a useful proxy in carbonate platform settings for the base of the Cenomanian ( Gale et al., 1996; Tröger & Kennedy, 1996; Velić, 2007; Simmons & Bidgood, 2023).

Nonetheless, there is evidence that O. concava can be found in middle Cenomanian strata. Bilotte (1984) illustrated reasonable O. concava from the middle Cenomanian of the Pyrenees, an observation also made by Caus et al. (2009) without illustration. Co-occurrence with Praealveolina cretacea (d’Archiac, 1837) or Praealveolina debilis Reichel, 1936 supports this assertion. El Sheikh & Hewaidy (1998) reported O. concava from the middle Cenomanian of Egypt (with Praealveolina tenuis Reichel, 1933 ), but the illustration is inconclusive. In the Adriatic Platform, Velić (2007), considers the species as occurring in the early and middle Cenomanian (see illustration in Velić, 1988). It is interesting to note that Schroeder (1975) placed the range of “ O. concava concava ” in the overlap between a twofold subdivision of the Cenomanian, thereby implying extension into the middle Cenomanian, a view he presumably changed in the ten years subsequent.

Although sometimes reported (but seldom illustrated) from late Albian strata (e.g., Decrouez & Moullade, 1974; Bilotte et al., 1978; Moullade et al., 1985; Görög, 1993; Ahmadi et al., 2008; Afghah et al., 2020), it may be that these records are actually of ancestral Orbitolina species or of O. concava sensu lato (herein Orbitolina spp. ) (e.g., Rey et al., 1977 – see Berthou & Schroeder, 1978), or that the late Albian age is unproven, so are herein discounted.

In the literature on the Middle East, there are some misleading statements about the range of O. concava ( Schlagintweit & Simmons, 2022) . For example, Haftlang et al. (2020) misquote the literature suggesting that Schroeder et al. (2010) indicated that O. concava is an Albian species (and thereby justifying a possible Albian age for rocks in which they supposedly find this species – the illustrations are indeterminate). There is no such statement that O. concava is an Albian species in Schroeder et al. (2010). Other records of O. concava from the Albian of the Iranian Zagros ( Kalantari, 1976; Keshavarzi et al., 2020, 2021) are indeterminate and must be doubted. An illustrated record from the potentially late Albian Maududd Formation of southern Iraq ( Manhi & Alsultani, 2021) is indeterminate.

Palaeogeographic distribution: Excepting an interesting record from eastern Europe (Chernov, 1970), the majority of viable records of this species are from western Europe. Although widely reported from the Arabian Plate (including the Zagros), most records cannot be confirmed as this species due to the illustrated specimens being unsuitable for definitive identification (e.g. Mohammed, 1996; Ameen & Gharib, 2014; Farsi et al., 2022). Amongst the possible records are those of Schlagintweit & Yazdi-Moghadam (2020, 2021, 2023) and Yazdi-Moghadam & Schlagintweit (2020, 2021, 2022), although as previously noted, they use the term “ Orbitolina gr. concava ” to designate a degree of uncertainty, given the need to access both suitable axial and tangential sections to observe all the relevant features to confirm identification. Thus, they are herein included within Orbitolina spp. (see below). The records of Weidich & Al Harithi (1990) from the Albian/Cenomanian transition of Jordan, seem to conform to O. hensoni .

Simmons et al. (2000) noted that the species appears to be absent from the F.R.S. Henson and Associates Collection in the Natural History Museum, London, which is based on Middle East material. Henson (1948: fig. 46) provided a detailed drawing of an embryo of ‘ O. concava vars.’ Displaying a broad peri-embryonic zone, this specimen can be referred to Palorbitolinoides Cherchi & Schroeder (compare Schlagintweit et al., 2022: fig. 5n).