Fissidentalium badense ( PARTSCH in HÖRNES , 1856 ) from the Badenian deposits of the south and southwestern margin of the Pannonian Basin System ( Central Paratethys )

The Badenian (Middle Miocene) Scaphopoda from the south and southwestern margin of the Pannonian Basin System (Central Paratethys) are poorly documented, and in published papers mostly presented by short lists of identified species. For the present study, 300 scaphopod specimens were examined with the focus on a singular species, Fissidentalium badense (PARTSCH in HÖRNES, 1856). This species is represented by 152 specimens housed in the Natural History Museum Belgrade and the Croatian Natural History Museum in Zagreb. The most numerous and the best preserved specimens of F. badense were collected at the Višnjica locality near Belgrade (Serbia), while the others originate from the vicinity of Zagreb (Croatia) and Ugljevik (Bosnia and Herzegovina). from the investigated area belong palaeogeographically to the south and southwestern margin of the Central Paratethys, and geotectonically to the Pannonian Basin System, surrounded by the Alps, Carpathians and Dinarides (Fig. 1) (e.g. RÖGL 1998, 1999; PAVELIĆ, 2001, 2002; PILLER et al., 2007). The beginning of the Badenian epoch is marked by a marine transgression, which flooded the areas behind the newly uplifted mountain chains (Paratethys) and was also prominent in the Medi­ terranean (Fig. 1) (RÖGL, 1998, 1999; KOVÁČ et al., 2007). Ac­ cording to numerous papers, the Badenian deposits of the south and southwestern margin of the Central Paratethys lie discorda­ ntly on the older Miocene, Mesozoic or even Palaeozoic deposits. The contact with basal rocks is in many places unclear or erosive or tectonic in character (e.g. ŠIKIĆ et al., 1978, 1979; BASCH, 1983a, b; VRABAC & MIHAJLOVIĆ, 1990; ANĐEL KOVIĆ et al., 1991; PAVELIĆ, 2001, 2002; SAVIĆ et al., 2005; PIKIJA, 2009). At the southern margin of Central Paratethys, F. badense is recorded in the Lower Badenian deposits of Serbia (wider Bel­ grade region) (PETKOVIĆ et al., 1976), in the assumed Lower to Middle Badenian of western Serbia (ŽUJOVIĆ, 1889; PAVLOVIĆ, 1903; STEVANOVIĆ, 1949; PETROVIĆ, 1967), and in the Lower Badenian (Upper Lagenidae zone) in northeastern Bosnia and Herzegovina (Bogutovo Selo) (VRABAC et al., 2013, 2014; PE­ ZELJ et al., 2013) (Fig. 1). In the area of the southwestern margin of the Central Paratethys, this species is present in the Miocene (probably Lower Badenian) marls of the wider Zagreb region (Med vednica Mt., Čučerje area) (KOCHANSKY, 1944, 1957; ĆORIĆ et al., 2009), and in the assumed Middle to Upper Bade­ nian deposits of the Samobor area (Vrhovčak locality, previously known as „Zaprešić Breg“ or „Zaprešić brijeg“) (ŠUKLJE, 1929; PAVLOVSKY, 1957, 1960; BAJRAKTAREVIĆ, 1978; VRSALJ KO, 2003; BAKRAČ et al., 2010). In the Badenian sediments of the Glinsko Pokuplje area, this species is found at one locality (PI­ LAR, 1873). Article history: Manuscript received December 16, 2015 Revised manuscript accepted May 31, 2016 Available online June 28, 2016


INTRODUCTION
The Scaphopoda is a class of Mollusca, also known as the "tusk shells".Their shell is tubular and generally curved, having open ings at both ends.Scaphopods are a cosmopolitan marine infau nal species, and live from the intertidal zones down to depths of more than 6000 m.Scaphopod species mostly burrow in sand or mud, with their head pointed downwards, and the narrow poste rior end of the shell protruding above the substratum (KNUD SEN, 1964;LAMPRELL & HEALY, 1998 and references therein;HABDIJA et al., 2011).
Although the scaphopod systematics have been revised over a few decades, the time of their appearance is still a matter of debate, as are their phylogenetics, so they are considered to be a puzzling molluscan class.Two orders of scaphopods are known: Dentaliida and Gadilida, which differ both morphologi cally, in shell and foot form, and behaviourally, in different bur rowing activities (LAMPRELL & HEALY, 1998 and references therein;STEINER & KABAT, 2001, 2004).
This paper focuses on the Badenian dentaliid species Fissi dentalium badense (PARTSCH in HÖRNES), recorded in the Mio cene deposits of the Paratethys, and widely distributed in Ba denian sediments of the Central Paratethys (e.g.BALDI, 1960;KOJUMDGIEVA & STRACHIMIROV, 1960;BALLUK, 1972;TITA, 2007;HARZHAUSER et al., 2011).Specimens of F. ba dense included here were collected from the Badenian sediments of the south and southwestern margin of the Central Paratethys (Croatia, Bosnia and Herzegovina and Serbia).The analyzed spe cimens are housed at the Natural History Museum Belgrade (NHMB) and Croatian Natural History Museum (CNHM).The first finding of F. badense from Bosnia and Herzegovina is pub lished here.

MATERIALS AND METHODS
Three hundred scaphopod shells were examined, and 152 of them belong to the species Fissidentalium badense (PARTSCH in HÖRNES).All the analyzed specimens are damaged, mostly in the apex area, and the majority of specimens are preserved as shell fragments.
NHMB specimens were collected at the Višnjica locality (wider area of Belgrade), and they are a part of the P. Pavlović collection, assembled in 1897 (90 specimens) and the P. Ste va nović collection, assembled in 1962 (40 specimens).Other spec imens come from the Loznica area in western Serbia (3 speci mens), and Bogutovo Selo near Ugljevik, Bosnia and Herzegovina (1 specimen).
CNHM specimens originating from the wider Zagreb region are part of the "Marine Miocene fauna of the southern part of the Medvednica Mt." collection (10 specimens) and the "Miocene fauna of Zaprešić Breg near Samobor" collection (5 specimens).Specimens from the third locality are part of the "Miocene and Pliocene fauna from the Glinsko Pokuplje area and Zrinjsko Dvorska valley" collection (3 specimens).
Description: Shell is medium to large, solid, moderately curv ed, narrow and elongated, open at both ends.Dorsal side is concave, and the ventral is convex.The apex is damaged in all the collected specimens.The shell narrows and slightly curves to the wider anterior opening.The shell is ornamented with solid radial ribs and growth lines.Sharp and moderately high, 8 to 10 radial ribs are near the apical area.Ribs become lower and almost flat near the wider end of the shell.Secondary ribs are inserted  between the primary ribs at various distances from the apex.The maximum number of inserted ribs near the posterior part of the shell does not exceed 30.The primary and secondary ribs at the posterior side of the shell are almost indistinguishable from each other with only minor differences.The species varies in number and thickness of the secondary ribs.Concave interrib spaces vary in width.Together with the radial ribs, fine and dense irregular growth lines (except in the apical area) characterize the shell sur face.The crosssection of both ends is subcircular.

DISCUSSION
In the Badenian sediments of the south and southwestern margin of the Central Paratethys, the majority of scaphopod discoveries belong to the dentaliids.Here, we analyzed and revised Fissiden talium badense (PARTSCH in HÖRNES, 1856) specimens stored at the NHMB and CNHM.Given the number of the recorded dentaliids, Višnjica near Belgrade (Serbia) is the site yielding the largest number of specimens.
All the published data and records suggest that F. badense mostly lived in muddy and muddysandy substrate at all the stud ied localities in Serbia, Bosnia and Herzegovina and Croatia.This species was widespread during the Lower Badenian, with fossil evidence from the clayey sediments of Austria (BadenSooss) (RÖGL et al., 2009), Romania (Lăpugiu de Sus) (TITA, 2007), Slovakia (BALLUK, 1972;HARZHAUSER et al., 2011), Hungary (BALDI, 1960) and Bulgaria (KOJUMDGIEVA & STRACHIMI ROV, 1960).The distribution of F. badense indicates the contem porary marine connections and migration routes.Due to the re corded and aforementioned findings, possible migration routes of F. badense to the area of Paratethys could be the southwestern ("Transtethyan corridor") and the northern marine passages (e.g.RÖGL, 1998;STUDENCKA et al., 1998;KOVÁČ et al., 2007).

CONCLUSIONS
This paper presents the scaphopod species Fissidentalium ba dense (PARTSCH in HÖRNES, 1856) housed at the Natural History Museum Belgrade and the Croatian Natural History Museum.Fossil material was collected from the Badenian (Middle Mio cene) deposits of the south and southwestern margin of the Cen tral Paratethys.
The age of the analyzed specimens from Serbia and Bosnia and Herzegovina stored at the Natural History Museum Belgrade is the Lower Badenian, while other Middle Miocene findings are questionable in age and require further research.
During the upper part of the Lower Badenian, the species had a wide geographic distribution, which implys an open marine connection of the Central Paratethys with other marine areas.
According to the available fossil record, Fissidentalium badense lived on a muddy to muddysandy substrate.

Fissidentalium
badense (PARTSCH in HÖRNES, 1856) from the Badenian deposits of the south and southwestern margin of the Pannonian Basin System (Central Paratethys)

Figure 1 .
Figure 1.Geographic and paleogeographic setting of the investigated area with marked localities containing recorded dentaliids (after KOVÁČ et al., 2007).

Figure 2 .
Figure 2. Morphometric measurement parameters: L − length, Max -maximum diameter, Dmax -maximum distance from the anterior opening, Arc -curvature maximum, Larc − maximum length from the apex to the deepest point of the curvature, Ha − height of the ventral opening, Wa − width of the ventral opening, Hp − apical height, Wp − apical width (after STEINER, 1999; SILVA-FILHO et al., 2012).