Parajanischewskina Cózar and Somerville, 2006

Liu, Chao, Vachard, Daniel, Cózar, Pedro & Coronado, Ismael, 2023, New species and evolution of the foraminiferal family Janischewskinidae in the middle-upper Mississippian of South China, Palaeontologia Electronica (a 2) 26 (1), pp. 1-27 : 19

Genus Parajanischewskina Cózar and Somerville, 2006

Type Species. Parajanischewskina brigantiensis Cózar and Somerville, 2006 .

Diagnosis. Janischewskinidae with slightly endothyroidal inner whorls and planispiral final whorls. Cribrate aperture in the final chambers and secondary sutural apertures with large pores. Thin, dark, and microgranular wall in most whorls, possibly formerly perforate, with an outer, darker layer. Keriotheca composed of an outer dark microgranular layer and an inner alveolar layer is present in the final septa and in the wall of the final chambers.

Composition. Parajanischewskina brigantiensis Cózar and Somerville, 2016 ; P. nautiliformis sp. nov.

Remarks. The genus Parajanischewskina was interpreted by Cózar and Somerville (2006) as an intermediate form between Bradyina and Janischewskina , mostly due to the stratigraphic record of these three genera in Britain. However, the biostratigraphy of these genera in other basins does not support the phylogenetic lineage. Parajanischewskina is restricted in Britain to the uppermost Asbian to the lowermost Brigantian ( Cózar and Somerville, 2004; Waters et al., 2017; Cózar et al., 2022), whereas the first Janischewskina ( J. typica ) occurred in the late Brigantian (= early Serpukhovian) ( Cózar and Somerville, 2021), as a result, there is a significant gap without any representatives of both genera. Richer Janischewskinidae assemblages from the Russian Platform show small species of Janischewskina from the Aleksinian ( FAD), at coeval levels with Bradyina , whereas the large species of Janischewskina occur from the Mikhailovian ( Kabanov et al., 2016; Gibshman et al., 2020). Parajanischewskina has been never reported from the Russian Platform, and as mentioned previously, it was questioned if the keriotheca might be an artifact of oblique sections over double or triple cribrate apertures. However, the case can be the contrary, and the keriotheca wall in the final chambers might be confused with oblique sections of cribrate apertures (e.g., Gibshman et al., 2020, pl. 1, figs. 11‒12). Furthermore, although unrecognized by previous authors, the genus has been recorded by us in the Venevian in the Western Moscow Basin of the Russian Platform ( Figure 11A‒B ).

Occurrence. Latest Asbian to late Serpukhovian in Britain, questionable in the Brigantian of SW Spain, Serpukhovian of Ireland and NW Spain, latest Viséan to late Serpukhovian in France and Sahara Platform, late Serpukhovian in Ukraine ( Cózar and Somerville, 2006; Cózar et al., 2014a, 2018; Vachard et al., 2016). Venevian in the western Moscow Basin, questionable in the Serpukhovian (Khudolazian) in the Urals. The FAD of the genus Parajanischewskina might be in the late Viséan, equivalent to the Aleksinian or Mikhailovian in the Donets Basin, Ukraine (C vf 1 2 horizon) ( Cózar and Somerville, 2006). It must be noted that the FAD of Janischewskina is located in the Aleksinian (e.g., Gibshman et al., 2020), and thus, it is not clear yet which genera, Parajanischewskina or Janischewskina , occurred first.

Distribution in the Bama Platform. Parajanischewskina brigantiensis ( Figure 11 C-D) has been recorded from the upper part of the latest Viséan, whereas P. nautiliformis only occurs at the base of the Serpukhovian in both sections. The former species disappears at the base of the lower Serpukhovian, whereas the latter extends up to the top of the lower Serpukhovian.

Figures

FIGURE 11. Typical representatives of the genus Parajanischewskina. A‒B. Parajanischewskina brigantiensis Cózar and Somerville, 2006, A. 3889-181, B. 3889-182, Limestone A8, top Iogla Formation, right bank of the Msta River, Western Moscow Basin (see Savitsky et al., 2015 for stratigraphical details). C‒D. Parajanischewskina brigantiensis, C. HPU-KC75-5, D. HPU-SDB143-16. E‒I. Parajanischewskina nautiliformis sp. nov., E. HPU-KC87-26, F. HPU- KC75-391 (holotype) G. HPU-KC87-487, H. HPU-KCT4-4, I. HPU-KC75-484. (Scale bar equals 1 mm).