Spirocyclina atlasica Saint-Marc & Rahhali, 1982

SIMMONS, MICHAEL & BIDGOOD, MICHAEL, 2023, “ Larger ” Benthic Foraminifera Of The Cenomanian. A Review Of The Identity And The Stratigraphic And Palaeogeographic Distribution Of Non-Fusiform Planispiral (Or Near-Planispiral) Forms, Acta Palaeontologica Romaniae 19 (2), pp. 39-169 : 90-93

Spirocyclina atlasica Saint-Marc & Rahhali, 1982

Reference Illustration & Description

Saint-Marc & Rahhali (1982), p. 134-136, pls. 1-2.

The genus Spirocyclina has a rather scattered stratigraphic distribution from the Late Jurassic (Kimmeridgian) to the Late Cretaceous (Santonian) (see Maync, 1959b, for a review up to that date and an emended redescription of the type species and the genus). However, it had not been recorded from the Cenomanian (and the mid-Cretaceous as a whole) until Saint-Marc & Rahhali (1982) described a new species, S. atlasica , from the Late Cenomanian of the Moroccan Atlas.

It is assigned to the Spirocyclinidae ( Loeblich & Tappan, 1988; Kaminski, 2014) together with Reissella and others. Saint-Marc & Rahhali’s figures (1982) show a form about 1.4mm across which is a symmetrically flattened planispiral, but which uncoils in a distinctly, almost dramatically, peneropliform style. The generic characteristic of a double row of pores in the apertural face (which can increase to three rows in the later/final stage) is visible in suitably oriented thin-section. See the Species Key Chart (Appendix) for diagnostic and other characteristics.

Saint-Marc & Rahhali (1982) remark on the similarity between Spirocyclina and the Late Cretaceous genus Sornayina Marie. The latter genus forms a slightly more asymmetrical planispiral, has a lesser tendency to uncoil, and has a more randomly scattered cribrate aperture and a much more acute periphery.

Reissella ramonensis differs in not being as flattened as S. atlasica . It also has a single main aperture with smaller secondary pores scattered across the apertural face, rather than two rows of openings.

Stratigraphic Distribution

Late Cenomanian.

Saint-Marc & Rahhali (1982) recorded S. atlasica from the late Cenomanian of Morocco. Further illustrated late Cenomanian Moroccan records are provided by Ettachfini (1993, 2006); Charrière et al. (1998), and Ettachfini et al. (2005), along with unillustrated records (e.g., Ciszak et al., 1999).

The record of Spirocyclina sp. from the late Cenomanian of SE France by Rineau et al. (2021) appears to be better referred to Pseudorhapydionina dubia .

Cenomanian Paleogeographic Distribution

North Africa.

In addition to the records from various parts of Morocco discussed above, the species is plausibly illustrated from Libya ( Dufaure et al., 1984) where its presence is used to infer a late Cenomanian age for the strata it occurs in.

Cenomanian ‘nummoloculinids’

Of all the taxa discussed in this review, the ‘nummolculinids’ exemplify the issues to be overcome in establishing an understanding of stratigraphic and palaeogeographic distribution of taxa. The identity of species is uncertain or disputed, names have been used as “buckets”, no matter if material is sufficent for identification, or, more often, if it is not. This was recognised by Radoičić (1978), and more recently by Schlagintweit (2008) and Piuz & Vicedo (2020). Of the 150 or so papers that we know of that mention Cenomanian ‘nummoloculinids’, the majority lack illustration to confirm identification, notwithstanding the difficulties in doing so. The inevitable end-result is a smearing of ranges. Furthermore, single random sections of nummoloulinds may be confused with other taxa that show some broad similarities in coiling mode (and vice versa).

These include genera such as Vidalina Schlumberger , Spiroloculina d’Orbigny , Idalina Schlumberger & Munier-Chalmas , alveolinids such as Ovalveolina Reichel and Cisalveolina Reichel , and also inlcudes the Lower Cretaceous Derventina Neagu (see for example Arnaud-Vanneau 1980, pl. 86 and Schlagintweit, 1991).

The Cretaceous (Albian - Cenomanian) ‘nummoloculinids’ are a group of broadly similar miliolids whose taxonomy, with some exceptions, remains unstabilised but which have frequently been associated with the Neogene genus Nummoloculina in the literature. Six “taxa” in three, possibly more, genera are included here. The authors feel that treating them together is a useful way of discussing their similarities/differences and their stratigraphic and paleogeographic distribution, although a full taxonomic review is necessary.

As noted above, the literature for this group is fairly extensive but suffers from a lack of suitably oriented specimens by which critical diagnostic features are visible. It is not uncommon to see views of tens of specimens with only a few showing some diagnostic features and very few (if any) showing all diagnostic features together.

The more-or-less common feature of the group is that they are miliolids (unlike all other taxa in this work) and are planispirally (or nearly so) coiled in the adult stage, hence their inclusion in this work. However, their early stages (after the proloculus) can be variously planispiral, streptospiral or milioline (up to quinqueloculine). The size of the early post-prolocular stage and the point of its transition to the planispiral or near-planispiral, adult stage can vary, especially between micro- and macrospheric generations. They can vary in external shape from a broad, rounded disc to almost spherical in overall form, and their apertures can also vary as can some internal features. This makes separation of species often extremely difficult.

Much of the introductory remarks on these taxa are taken from Schlagintweit (2008) and Piuz & Vicedo (2020), who have described aspects of the taxonomic history of this ‘group’. The genus Nummoloculina was first described by Steinmann (1881) for material from the Miocene of Austria. Several species attributed to the genus Nummoloculina (or Nummoloculina -like genera) recorded from the Albian (or older) to the Maastrichtian exist in the literature, and are widely recorded from Mexico to Oman. However, Nummoloculina as most recently defined (see Loeblich & Tappan, 1988) is demonstrably a Neogene genus. The genus or ‘group’ was not discussed by Schroeder & Neumann (1985) in their extensive treatment of Cretaceous LBF.

The genus Pseudonummoloculina was established by Calvez from the Albian of France ( Calvez, 1988) for taxa formerly assigned to Nummoloculina but with a notched aperture and a quinqueloculine early stage. He designated the type species of this genus as P. aurigerica . As a consequence, some other Cretaceous ‘ Nummoloculinas ’ were thenceforth also regarded as Pseudonummoloculina by, for example, De Castro (1987) and Hottinger et al. (1989) (e.g., regarding “ Nummoloculina heimi ”). This would, of course, require these taxa to possess notched apertures. The visibility of the notched aperture in thin section depends entirely on a fortuitous thin section orientation and cut and the vast majority of illustrated specimes do not feature this crucial diagnostic character. When first describing N. heimi for example, Bonet (1956) stated “ Apertural characters not observed despite its abundance.” The debate on whether the taxon referred to as heimi posesses a notched (or sometimes referred to as ‘crenulated’) aperture still continues (e.g., Piuz & Vicedo, 2020, and see below).

In general, it seems that most Cretaceous ‘nummoloculinids’ do not appear to posses notched apertures with the exceptions of P. aurigerica (type species of Pseudonummoloculina ) (also see the Maastrichtian P. kalantari Schlagintweit & Rashidi, 2016 ) and the new species of Piuz & Vicedo (2020) P. gnosi (type species of Planinummoloculina – see below) – placed in a separate genus because it is basically planispiral throughout, lacking a post-prolocular milioline or streptospiral stage. Some taxa below are therefore questionably assigned to Pseudonummoloculina for practical purposes here only, and we recognise that a new genus (or even new genera) could be created for these taxa.

Piuz & Vicedo (2020) identified and described two new ‘nummoloculinid’ genera and species ( Planinummoloculina gnosi and Nummoloculinodonta akhdarensis ) from two separate levels within the Cenomanian Natih Formation of Oman. They state “ Both populations are architecturally different from any other species of ‘nummoloculinas’ described so far…” but include some records of ‘nummoloculinid’ taxa in possible synonymy.

Other putative ‘nummoloculind’ taxa recorded from Cenomanian or proximate strata include the aforementioned P. aurigerica from the Albian of France and a form from the Albian-Cenomanian of southern North America (and also found elsewhere) – P? ex. grp. heimi (Bonet) – see also Conkin & Conkin (1958) and Piuz & Vicedo (2020) for a discussion of P? ex. grp. heimi . A taxon known as N. regularis Philippson is also discussed and also questionably reassigned to Pseudonummoloculina .

Another taxon is Nummoloculina irregularis first described from the Santonian of Serbia ( Decrouez & Radoičić, 1977). Some authors have identified and illustrated forms assigned as N. cf. irregularis to sediments of Turonian – Santonian age (e.g. Chiocchini et al., 2012). Some ‘nummoloculinid’ specimens which appear to continue across the Cenomanian-Turonian boundary (e.g. those of Solak et al., 2020 identified as Pseudonummoloculina sp. ) have been compared to these N. cf. irregularis forms and therefore justifies including in the discussion herein.

The six taxa included here in this ‘group’ are therefore:

• Pseudonummoloculina aurigerica Calvez

• Pseudonummoloculina ? ex. grp. heimi (Bonet emmend. Conkin & Conkin)

• Pseudonummoloculina? regularis (Philippson) sensu Chiocchini et al. (2012) :

• Pseudonummoloculina ? cf. irregularis ( Decrouez & Radoičić, 1977) sensu Chiocchini et al. (2012)

• Planinummoloculina gnosi Piuz & Vicendo

• Nummoloculinodonta akhdarensis Piuz & Vicedo

Nevertheless, the group is in need of a thorough monographic review and re-examination of type material to better formalise species definitions and hence stratigraphic and paleogeographic ranges.