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Bispiraloconulus serbicus n. gen., n. sp., a giant arborescent benthic foraminifera from the Berriasian of Serbia
Felix Schlagintweit, Ioan I. Bucur, Milan N. Sudar

Building: Muséum d'Histoire Naturelle de Genève
Room: Amphithéâtre
Date: 2018-12-06 09:20 AM – 09:40 AM
Last modified: 2018-11-24

Abstract


A new giant (centimetre-sized) benthic foraminifera displaying arborescent morphology is described as Bispiraloconulus serbicus from Berriasian shallow-water carbonates of the Kurilovo area, eastern Serbia. The sample yielding the new taxon belongs to a carbonate succession outcroping north-north-east of Niš city, in the vicinity of Kamenica village. The limestones from this area belong to the Kurilovo fold structure or anticline that is part of the Gornjak-Stuva Planina unit, the westernmost part of the Carpatho-Balkanids of Eastern Serbia. North of the Danube River it continues with the Sasca unit belonging to the Getic domain of the South Carpathians. The dimorphic taxon is characterized by an adult part with rectilinear chambers, a thin wall (epiderm) with short polygonal subepidermal network (exoskeleton), and thin septa exhibiting cribrate foramina. The chamber interior contains a 3D-construction of (bio-)clasts fixed (agglutinated) to the septa and the exoskeleton by means of micritic columnar elements. All these features are characteristic for the genus Spiraloconulus Allemann & Schroeder (Aalenian-Berriasian) with its three species S. perconigi Allemann & Schroeder, S. giganteus Cherchi & Schroeder, and S. suprajurassicus Schlagintweit. The branching-arborescent test morphology, however, differentiates the Serbian form from Spiraloconulus being unbranched conical to cylindro-conical. Following current classifications of agglutinating foraminifera, test bifurcation is considered a generic criterion (e.g., compare Reophax vs Bireophax; see Loeblich & Tappan, 1987; Kaminski, 2014) and consequently a new genus was established: Bispiraloconulus. With this characteristic Bispiraloconulus can be compared with the Barremian-Aptian Torremiroella Brun & Canérot or the Cenomanian Thomasinella Schlumberger. Among the agglutinating foraminifera Bispiraloconulus is unique by its arborescent test combined with a wall displaying a subepidermal network. Bispiraloconulus belongs to a group of larger benthic foraminifera displaying internal agglutination that fills large parts of the chamber interior: Spiraloconulus Allemann & Schroeder (Aalenian-Berriasian), Bostia Bassoullet (Bathonian), Robustoconus Schlagintweit & Velić (Bajocian), and Torremiroella Brun & Canérot (Barremian-Aptian). Another allied taxon also displaying an exoskeleton and "large globular particles incorporated into the septa" (Loeblich and Tappan, 1986, p. 335) is Dhrumella Redmond, 1965 (Bathonian). Still poorly known, Dhrumella might also belong to this group and can be considered a compressed, peneropliform Spiraloconulus. This peculiar internal structure obviously contributed considerably to test rigidity allowing an adaptation to agitated shoal and near-shoal paleoenvironments. Delicate large-sized arborescent agglutinated taxa (with simple wall and lacking internal constructive elements) instead are reported from bathyal depths.