Zagrosella Schlagintweit & Rashidi, 2017

Schlagintweit, Felix & Rashidi, Koorosh, 2017, Zagrosella Rigaudii N. Gen., N. Sp., A New Biokovinoidean Foraminifer From The Maastrichtian Of Iran, Acta Palaeontologica Romaniae 13 (1), pp. 3-13 : 6-10

Genus Zagrosella Schlagintweit & Rashidi , n.gen., n.sp.

Type species: Zagrosella rigaudii n.sp.

Origin of the name: The genus name refers to the Zagros Mountains in the southwestern part of Iran.

Horizon and locality: Late Maastrichtian limestones of the Tarbur Formation of the Naghan section ( Figs. 1–2 ).

Description: Test free, rounded margin, oscillating coiling plane in the early stage, later planispiral, and finally maybe uncoiling, rectilinear. Dimorphism is most likely present. Proloculus of the megalospheric form elliptical to globular, with a large or few openings followed by entotebid-shaped chambers significantly increasing in width and height within a few whorls. Chambers in the adult uncoiled stage are saucer-shaped. Chamber interior with few and irregularly distributed endoskeletal pillars preferentially in the youngest chambers. Wall thick, darkmicrogranular-like to agglutinated (= calcareous grains) with close-set simple unbranching parapores (pseudokeriotheca-like) displaying polygonal pattern in transverse sections; thin epidermis present, may be decorticat- ed. Foramen basal to multiple in the juvenile stage, later multiple. In the adult part the width of the foramina almost attains the thickness of the massive septa. Possibly microspheric forms without observable proloculus, larger in diameter resulting from distinct broadening of chambers.

displaying a rounded margin. Dimorphism is most likely present. Assumed microspheric specimens without observable proloculus, and chambers broadening distinctly in the last whorl; tendency to uncoil not observable or not present ( Fig. 5H ). Proloculus of megalospheric form elliptical to globular, with a large or few openings followed by entotebid-shaped chambers significantly increasing in width and height up to 2.5 whorls. There are 11-16 chambers in the last whorl. Chambers in the adult uncoiled and rectilinear stage, usually two to three, rarely up to ten chambers (e.g., specimen in Fig. 3A ), and saucer-shaped. They may occasionally be arranged slightly off the coiling plane.

Chamber interior (mostly of the youngest chambers) with few and irregularly distributed endoskeletal structures (pillars) (e.g., Figs. 5C , 6H ). The diameter of the pillars is rather variable but generally reduced. Wall thick, dark, microgranular-like to agglutinated (= calcareous grains) with close-set simple (unbranching) parapores (pseudokeriotheca-like) arranged perpendicular to the surface; epidermis thin, but often may be eroded. In transverse sections, the parapores display a polygonal pattern ( Fig. 4A ). Foramen basal to multiple in the juvenile stage, later multiple. In the adult part the width of the few foramina almost attains the thickness of the massive septa.

Dimensions (in mm):

Diameter of proloculus: 0.16–0.31 (mostly 0.2–0.24) Equatorial diameter: up to 1.6

Axial diameter: up to 0.95

Height: up to 3 (e.g., specimen with long uncoiled part illustrated in Fig. 3A ).

Chamber height (lumen) enrolled stage: 0.08–0.12 Thickness of septa (adult stage): 0.08–0.12

Wall thickness: 0.06–0.1

Diameter of pillars: 0.02–0.04

Comparison: Zagrosella rigaudii n.gen., n.sp. is morphologically similar to Biokovina gradacensis Gušić, 1977 ( Fig. 8 ). The differences between both species are compiled in Table 1. It is worth mentioning here that the so-called phrenothekalike structures reported by Gušić (1977) from Biokovina , were interpreted by Schlagintweit and Velic (2012) as representing cryptoendolithic thaumatoporellaceans (incertae sedis) dwelling inside the empty chambers of dead foraminiferan shells. They are also reported from Zagrosella rigaudii n.gen., n.sp. ( Fig.

5D, Fig. 6B , 7E, K–L ). Due to our interpretation these are not part of the foraminiferan test, and were therefore not included in the description. Inside empty and dead foraminiferan tests, they could obviously squeeze like a flexible tube (presumably under pressure) through the foraminal openings from one chamber to the next. The moving behaviour together with the occurrence in completely shad- ed microhabitats excludes the idea of thaumatoporellaceans belonging to photosynthetic algae (for further details see Schlagintweit and Velic, 2012 and Schlagintweit et al., 2013).

Figures

Fig. 1 Location of the studied area and Naghan sections.

Fig. 2 Vertical distribution (total range) of selected taxa of larger benthic foraminifera in the Tarbur Formation of the Naghan section.

Fig. 5 Zagrosella rigaudii n.gen., n.sp., upper Maastrichtian Tarbur Formation of the Naghan section, Zagros Zone, SW Iran. a, c, Equatorial sections, b, d–g, Oblique equatorial sections. h, Equatorial section of a microspheric specimen. Abbreviations: p = proloculus, pi = pillar, t = structures interpreted as cryptoendolithic thaumatoporellaceans. Thin-sections: NG 88 (a), 2NG 94 (b), 2NG 91 (c), 2NG 85 (d), NG 88 (e), NG 14 (f), 2NG 98 (g), NG 38-1 (h).

Fig. 3 Typical microfacies of samples with Zagrosella rigaudii n.gen., n.sp. (Z), from the upper Maastrichtian Tarbur Formation of the Naghan section. a–b Wackestones/packstones with benthic foraminifera, among many porcelaneous taxa, and remains of dasycladalean algae. Note the specimen with prominent enrolled stage and alternating pillars in the youngest chambers in a (right). Thin-sections: NG 8 (a), 2NG 85-4 (b).

Fig. 6 Zagrosella rigaudii n.gen., n.sp., upper Maastrichtian Tarbur Formation of the Naghan section, Zagros Zone, SW Iran. a– d, g, Oblique equatorial sections. e–f, h–i, Oblique sections. Abbreviations: p = proloculus, pi = pillar, t = structures interpreted as cryptoendolithic thaumatoporellaceans. Thin-sections: 2NG 98 (a), NG 92 (b), NG 91 (c), 2NG 85 (d), NG 49 (e), NG 86 (f), 2NG 84 (g), NG 83-2 (h), NG 84 (i)

Fig. 4 Wall-structure of Zagrosella rigaudii n.gen., n.sp. from the upper Maastrichtian of SW Iran (a–b) and Biokovina gradacen- sis Gušić from the Liassic of Croatia (c–d). Polygonal parapores are marked with an arrow in a. Thin-sections: 2NG 27 (a), 2NG 87 (b). Remarks and comparisons: The wall structure of Zag- the Late Cretaceous, it can be compared to some extent rosella with its “uniform, parallel, radial elements cov- (e.g., similar wall-structure, strengthenings) with Braciered by some kind of tectum” (Hottinger, 2006, p. 29) can ana Schlagintweit & Cvetko-Tesovic, 2016 (Santonian?- be compared with the keriotheca-like (or pseudokerithe- lower Campanian of Croatia). The latter differs from cal) texture of some Mesozoic larger benthic foraminifera Zagrosella n.gen. above all by its test morphology (elon- (e.g., Schroeder et al., 1975; De Castro, 1981; Septfon- gate compressed), and the foraminal characteristics (sevtaine, 1981; Banner et al., 1991; Rigaud et al., 2015). eral close-set openings, equal in diameter to the wall al- Regarding differences to parapores (or canaliculi), the veolae, and may have short peristomal rims at their mardifferences are vague and not clearly delimited (Hot- gins) (see Schlagintweit and Cvetko-Tešović, 2016 for tinger, 2006: “usually much larger”…”often more irregu- details). lar”). Zagrosella n.gen. is morphologically very similar to Last but not least we note morphological similarities the Liassic Biokovina Gušić, 1977, both monospecific to the Late Jurassic Labyrinthina Weynschenk that differs genera. The wall structure of Zagrosella appears more above all from Zagrosiella by its wall being “agglutinatevolved with larger parapores (diameter 0.01 to 0.03 mm, ed, simple in structure, microgranular, imperforate” see description below) whereas in Biokovina these are (Loeblich and Tappan (1987, p. 96). thinner (but with overlapping range), and bifurcating (di- ameter ~0.01 to 0.15 mm). There are also differences in Zagrosella rigaudii Schlagintweit & Rashidi, n.sp. the endoskeletal structures, being more massive (in the Figs. 3 pars, 4a–b, 5–7 central part of the test) and may fuse in Biokovina where- Origin of the name: The species name refers to Sylvain as in Zagrosella they occur preferentially on the sides of Rigaud (Singapore) for his outstanding contributions to the chambers, sometimes only partially differentiated the micropalaeontology and phylogeny of benthic foramfrom the chamber wall, and never fused. They are here inifera. interpreted as pillars (originating from the septa), not as Holotype: Slightly oblique equatorial section illustrated septula (originating from the wall) (see Hottinger, 2006) in Figure 5A, thin-section NG 88. or strengthenings (see Rigaud et al., 2013). Another mor- Paratypes: Figs. 5B–G, 6, 7A–B. phologically similar genus of the family Biokovinidae is Description: Test free, lenticular, with oscillating plane Bosniella Gušić, 1977. It differs from Zagrosella above of coiling in the early stage, later planispiral, and finally all by its chambers lacking any endoskeletal structures. In maybe uncoiling, rectilinear. It is compressed axially,

Fig. 8 Biokovina gradacensis Gušić, Liassic of Croatia. Photographs made from the original thin-section material of Gušić (1977: A see plate 2, fig. 2, and B see plate 1, fig. 2).

Fig. 7 Zagrosella rigaudii n.gen., n.sp., upper Maastrichtian Tarbur Formation of the Naghan section (except i from the Mandegan section), Zagros Zone, SW Iran. a–b, Axial sections. c, Slightly oblique subaxial section. d, Subaxial section. e–l, Oblique sections. Abbreviations: f = foramen, pi = pillar, t = structures interpreted as cryptoendolithic thaumatoporellaceans. Thin-sections: 2NG 60-1 (a), NG 85 (b), 2NG 94 (C), 2NG 15 (d), 2NG 27 (e), 2NG 83 (f), 2NG 39 (g), NG 94 (h), Rt 67-3 (i), NG 90 (j), NG 86 (k), 2NG 85 (l).