Dictyoconella complanata Henson, 1948

SCHLAGINTWEIT, FELIX & RASHIDI, KOOROSH, 2021, Dictyoconella Henson, 1948, Upper Cretaceous Larger Benthic Foraminifera: A Taxonomic Revision With The Establishment Of Gusicella Gen. Nov. (Type-Species Dictyoconella Minima Henson), Acta Palaeontologica Romaniae 17 (2), pp. 3-13 : 7-10

Dictyoconella complanata Henson, 1948

Figs. 2 a-b pars, 3-4

1948 Dictyoconella complanata n. gen., n. sp. – Henson, p. 25, plate 6, figs. 2-3, 16, pl. 10, fig. 14.

1986 Dictyoconella complanata Henson – Köylüoğlu, pl. 86, fig. 1 pars.

1998 Dictyoconella complanata Henson – Whittaker et al., pl. 47, figs. 4-6.

2016 Dictyoconus bakhtiari Schlagintweit et al. – Schlagintweit et al., fig. 8g, fig. 10f.

2020 Dictyoconella complanata Henson –Schlagintweit, p. 75, fig. 4d-f.

Description: See the genus description.

Dimensions:

Test diameter: up to 4.8 mm (3.3 mm, holotype specimen of Henson, 1948)

Test height: 3.6 mm (2.9 mm, holotype specimen of Henson, 1948)

Thickness: mostly between 0.8 and 0.9 mm (~ 0.8 mm, Henson, 1948)

Number of chambers last mm axial length: 7-9 (about 7, Henson, 1948)

Remarks: The dimorphism of D. complanata is well constrained by the biloculine embryo in the A-form and an indiscernible embryo within a close-coiled whorl including more chambers in the B-form (one section only, see Fig. 4b ). The differences in the external test morphology between the two generations are unknown. In the family Orbitolinidae , B-specimens are generally larger and more flattened (e.g. Hofker, 1966). In the Iranian Tarbur Formation, D. complanata is comparably rare and only a couple of sections are available. Due to the revision presented herein, Dictyoconella becomes a monospecific genus and an assumed Maastrichtian newcomer that became extinct shortly afterwards at the K-Pg boundary. Besides the Tarbur Formation of Iran, D. complanata has been reported so far from the Maastrichtian Garzan Formation of southeastern Turkey ( Köylüoğlu, 1986) revealing some kind of bioprovincialism, which requires subsequent study ( Schlagintweit, 2020a).

Figures

Fig. 2 Microfacies with Dictyoconella complanata Henson (a-b) and Gusicella minima (Henson) gen. et comb. nov. (c- d) from the Maastrichtian Tarbur Formation of the Naghan (a-b) and Mandegan sections (c-d), SW Iran (Zagros zone). Abbreviations: D = Dictyoconella, Di = Dicyclina, G = Gyroconulina, Gu = Gusicella, L = Loftusia, O = Omphalocyclus, P = Pseudonummoloculina, Ps = Pseudocymopolia, T = Tarburina. Thin sections: 2Ng 81 (a), 2Ng 81-4 (b), Rt 109 (c), Rt 105 (d).

Fig. 4 Dictyoconella complanata Henson from the Maastrichtian of the Tarbur Formation of Iran (Naghan section, a-i, k) and the Simsima Formation of Qatar (j). a, d, oblique sections perpendicular to plane of compression. Note the inclination of the apical-juvenile part expressed by the parallel-sectioning of septum (s) and foramina (f) in d. b, oblique section passing through the initial part of a microspheric specimen. c, f, i-k, oblique sections in the plane of compression (j, paratype from Henson, 1948, pl. 10, fig. 14). Detail from i shows the fine subepidermal cellular network, marginal foramina and undivided marginal trough. e, g-h, oblique sections passing through the initial part of megalospheric specimens. Thin sections: 2Ng 81- 2 (a, d), Ng 76 (b), 2Ng 81-3 (c), Ng 85 (e), 2Ng 87-2 (f, i), 2Ng 80-1 (g), 2Ng 85-4 (h), 2Ng 81-1 (k). Abbreviations: b = beam, deu = deuteroconch, f = foramen m.f. = marginal foramen, m.t. = marginal trough, pi = pillar, pr = proloculus, T = Tarburina zagrosiana Schlagintweit et al. (in k).