M iddle Miocene Otoliths of Freshwater Fishes from the Vračević Lake (Serbian Lake System)

. The Serbian Lake System (SLS) is a key area on early to middle Miocene freshwater environments in southeastern Europe. Here, we describe a rich fossil association of freshwater fish otoliths of late Badenian to early Sarmatian (Serravallian, MN 7+8 zone) age. The studied material was collected from several small outcrops along the Grabovac stream near Vračević. The Vračević locations are part of the Valjevo-Mionica Basin (VMB). We identified nine different species, including two in open nomenclature and three new to science: Aphanius jeani, Aphanolebias bettinae n.sp., Klincigobius andjelkovicae, Klincigobus haraldahnelti n. sp., Klincigobius serbiensis, Klincigobius sp., Ponticola sp., Toxopyge campylus, Toxopyge vracevicensis n.sp. We found that the composition of this fish fauna correlates well with the slightly older fauna from the early to middle Miocene of Klinci. Both localities were most likely part of a continuous environment during the existence of the Valjevo-Mionica Basin. The composition of the community of freshwater gobies from the early to early middle Miocene of southeastern Europe indicates the presence of a "lost" Miocene freshvvater goby fish fauna that existed prior to and was unrelated to the Ponto-Caspian fish fauna that prevails today. The new data may prove help-ful in reconstructing the paleogeographical evolution of the Valjevo-Mionica Basin in detail. deep sulcus. Sulcus narrow, bow-shaped w ith regularly curving dorsal rim , and w ith o u t ostial lobe or subcaudal iugum. Sulcus inclination 10-15°. Colliculus distinctly sm aller than sulcus. Dorsal field w ith indistinct dorsal depression. Ventral field w ith distinct, deep, gently curved, short ventral fu rro w running from low er m argin of ostium to low er m argin of cauda. Area between ventral fu rrow and sulcus distinctly bulged. Outer face convex, smooth.


I n t r o d u c t i o n
The sedim ents o f the Neogene c o n tin e n ta l lacustrin e systems o f the states o f the fo rm e r Yugoslavia have been a subject o f research in te re s t am ong geologists and p a le o n to lo gists fo r m o re th a n a century.
In tra m o n ta n e basins in Croatia, Bosnia and Herzegovina, and Serbia co n ta in e d v a rio u s lo n g -liv e d freshvvater lakes d u rin g the late Oligocene and early to m id d le M iocene (e.g., Harzhauser & Mandic, 2008;M andic et al., 2010N eubauer e t al., 2011, 2015a, b, 2016 and references th e re in ). Generally, tw o large fre s h w a te r system s are recognized: the D in a rid e Lake System (DLS) and a yo u n g e r one, th e Serbian Lake System (SLS) (K rstić et al., 2003, 2007; D e L eeuw e t al., 2010;M andic et al., 2010Sant e t al., 2018a, b;N eubauer e t al., 2 0 2 0 ).
These tw o lake system s w e re fir s t recognized b y S. B ru s in a (1 8 4 5 -1 9 0 8 ), a p ro m in e n t z o o lo g is t and p a le o n to lo g is t fro m Zagreb. Today, a c e n tu ry and h a lf later, the a fo re m e n tio n e d a uth ors have b u ilt on B rusina 's p io n e e rin g w o r k and u n e a rth e d m ore deta ils c o n ce rn ing the "g re a t m osaic" o f a n cie n t lake systems. D u rin g the la s t 10 years, the DLS has been stu d ie d u sin g d iffe re n t approaches. In a d d itio n to co n ve n tio n a l m ethods, such as those o f b io s tra tigraphy, paleon tology, sedim entolo gy, and tectonics, in d e p e n d e n t c h ro n o s tra tig ra p h ic techniques, such as m a g n e to s tra tig ra p h y and ra d io m e tric age contro l, have also been a p p lie d (e.g., De Leeuw e t al.,  Leeuw et al., 2010Leeuw et al., , 2011M andic et al., 2010Sant et al., 2018a, b). D u rin g the last decade, s ig n ific a n t a tte n tio n has also been pa id Vračević paleo-lake and analyze the possible stratigraphic positions of the respective sediments. We found a total of 295 otolith specimens, from which we identify ten freshwater fish species in the sediments of the Vračević paleo-lake, two pertaining to the Cyprinodontidae and seven to the Gobiidae. The composition of the fauna shows some congruence between the Vračević paleo-lake and neighboring Valjevo paleo-lake but also certain differences, which may indicate a difference in time between the two basins.

Geological Setting
Vračević village, which lies north of Mionica in western Serbia, is situated within the large Valjevo-Mionica Basin (VMB; Fig. 1A). The Dinaride basin belongs to a series of Miocene intramontane basins that are distributed across Serbia (Simić et al., 2017;Bradić-Milinović et al., 2018. It covers an area of 350 km 2 and represents the western part of the Valjevo-Mionica-Belanovica Graben (Marović et al., 2007). This two-part graben (Valjevo-Mionica is in the western part and Belanovica in the east) was formed during the Ottnangian-Karpatian and the early Middle Miocene (early Badenian); it became inverted and subject to moderate or weak uplifting in the Quaternary (Marović et al., 2007). Based on previous studies as well as data obtained from new drillings, a few cycles of sedimentary rocks and volcano-clastites (ranging from lacustrine to reduced marine and brackish sediments) may reach thicknesses of up to 1,000 m in the center of the basin (e.g., Obradović & Vasić, 2007). The western part of the VMB (Valjevo area) is filled with a succession of lacustrine early Miocene sediments that commonly contain oil shales at the base with tuff intercalations and otherwise consist of sandstone and mudstone to limestone with gravel. Quaternary alluvial and diluvial-proluvial deposits are widely distributed at the surface ofthe basin area (Bradić-Milinović et al., 2019 and references therein). The VMB was largely formed on the Jadar block (JB), which represents a northern part of the Jadar-Kopaonik thrust sheet derived from the most distal Adriatic passive margin (Schmid et al., 2008;Neubauer et al., 2016;Bradić-Milinović et al., 2019). The JB is composed of Devonian and Carboniferous predominantly shallow-marine carbonates and a flysch series overlain by Permian and Triassic shallow-marine carbonates that were obducted in the Jurassic by ophiolites of the VVestern Vardar Ocean (Schmid et al., 2008). The eastern part of the VMB betvveen the Toplica and Ljig Rivers (Vračević, Mionica area) is characterized by restricted marine and lacustrine deposits of Sarmatian and Pannonian age (middle and late Miocene; Fig. 1B).
Lithostratigraphically, the above-mentioned sediments correspond to the Vračević Formation Obradović & Vasić, 2007;Lazarević et al., 2013;Rundić, 2017;Bradić-Milinović et al., 2019;Fig. 2). According to most earlier studies, there is no transition between the lower Miocene lacustrine sediments and the middle Miocene marinebrackish ones (e.g., . In other words, the Sarmatian restricted-marine sediments are transgressive and unconformable over the lowermiddle Miocene lacustrine sediments (Jovanović & Dolić, 1994;Dolić, 1995;Lazarević et al., 2013). In addition, there is an ongoing debate concerning the interrelationships among the VMB lacustrine basins in time and space. Much more detailed and varied stratigraphic methods and radiometric age control are required to clarify this issue. The Vračević (Mionica) area is an east-west striking elongated small basin (ca. 70 km long and 15 km wide) formed in the middle Miocene during the maximum extension phase ofthe southeastern Pannonian Basin (Matenco & Radivojević, 2012;Rundić, 2017;Rundić etal., 2019) that coincided with the Middle Miocene Climatic Optimum (MMCO; Mandic et al., 2010Mandic et al., , 2012Neubauer et al., 2015a, b). The Vračević Basin represented an isolated lacustrine basin that was occasionally flooded from the north by Paratethyan marine-brackish waters during the early to middle Miocene and subsequently by Lake Pannon caspi-brackish waters (similar to water the mineralization in the contemporary Caspian Lake).
Paleontological research has been conducted for more than 70 years near Vračević. Among the first researchers, Laskarev (1948) (Marković, 2003), fre sh w a te r m ollusks (Prysjazhnjuk et al., 2000;Kovalenko, 2004;Prisyazhnyuk & Rudyuk, 2005], and terre stria l gastropods (Neubauer et al., 2016] Six sm all outcrop sections (up to 2.5 m high) revealed pred o m in a n tly fine-grained clastic freshw ater deposits (Fig. 3). Genus Aphanolebias Reichenbacher & Gaudant, 2003 Aphanolebias bettinae n. sp.  OL:OH = 1.1 2-1.2 8 ; OH:OT = 2.7-3.0. R ostrum relativ e ly slender, pointed, 1 9 -2 6 % o f OL. Excisura deep and sharp; a n tiro s tru m b lu n te r th a n ro s tru m and so m e w h a t sh orte r, 1 2 -1 6 % o f OL. P re do rsal rim steeper th a n po stdo rsa l rim , the la tte r often s lig h tly curved; v e n tra l rim shallow , m o d e ra te ly curved. A ll rim s sm ooth o r s lig h tly and irre g u la rly u n d u la tin g . andjelkovicae o r another, closely re la te d species. We th e re fo re allocate th e m te n ta tiv e ly to K. andjelkovicae, w h ile a d d itio n a l specimens w o u ld p ro b a b ly rectify the id e n tific a tio n .
K lincigobiu s h a ra ld a h n e lti n. sp. iugum sm all, b e lo w a n te rio r p a rt o f cauda, often ind is tin c t. D orsal depression in d is tin c t, n a rro w ; d orsal fie ld a n te rio rly narrow ed. V entral fie ld re la tive ly w id e w ith d is tin c t, deep, and g e n tly and re g u la rly curved v e n tra l fu r ro w ru n n in g fro m a n te rio r tip to p o s te rio r tip o f sulcus and c lip p in g a n te rio r and

E v a l u a t i o n a n d D is c u s s io n S tr a tig r a p h ic c o n s id e r a tio n s
The and Marković & Mili vojević (2010), who concluded that the fauna belongs to zone MN 7/8. Marković & Milivojević (2010) placed the vračević Formation in the Sarmatian s.s., but the mammal zone MN7/8 actually extends over the late Badenian and the Sarmatian s.s. (GradSteiN et al., 2012). in the assessment of the non-marine mollusks from vračević, NeuBauer et al. (2016) also concluded that they dated to the Sarmatian s.s.. However, our analysis of the fish otoliths shows a close relationship with that of klinci, which is considered to be of late early to early middle Miocene age (Bradić-MiliNović et al., 2019), and no resemblance to any of the relatively well-known Sarmatian s.s. fish associations from the Central Paratethys and its marine-brackish water transitional realms. While this difference is certainly to a significant extent due to paleoenvironmental differences, in our opinion, it points to a slightly older age than Sarmatian s.s., perhaps late Badenian.
during the fieldwork conducted in 2019, specific samples were taken for microfossil and palynological analysis. the palynological evaluation showed that the moist lower area around the paleo-lake was inhabited by grassy and shrubby plants (Compositopollenites, Tubifloridites, Nyssa, Taxodium, taxodiaceae-Cupresaceae, Polypodiaceae ferns, Shizaceae) and that the somewhat drier parts were inhabited by Carya, Engelhardti, Corylus, Betula, Myrica, ericaceae, and Sapotaceae. the interior region of the mainland, the coastal and hilly areas, were occupied by deciduous forests (Quercus, Castanea, Platanus, juglandaceae, Castanopsis, Rhus, Tilia, and others), while the hilly mountainous areas were inhabited by representatives of conifers (Pinus, Picea, Abies, Podocarpus, and Cedrus). Considering the large amounts of coniferous pollen in almost all of the prepared sample, it appears that the lake was open to the hilly mountainous environments nearby, allowing the pollen to be carried by the wind and deposited in the sediments. Furthermore, it is noticeable that the samples did not contain much organic matter, such as large plant tissues or other fragments of organic matter. the identified genera and species indicate the presence of a warm, Mediterranean-type vegetation. their dominance is evident in relation to the completely sporadic presence of cool-temperate types found in younger Neogene sediments (middle Miocene). the plant association is interpreted to have existed in a warm, relatively humid climate, with sporadic representatives of a drier climate. this palynological association is characteristic of the MN7 zone, ranging from the upper Badenian to lower Sarmatian s.s.
We expect that future research on a greater geographical area (e.g., the small streams around Gornji Mušić) as well as radiometric dating of tuffs within this series could result in a more precise chronostratigraphic dating of the Miocene vračević lake.

Faunal Comparison and Evolution
Setting the scene. the middle Miocene was a time of global climate change, expressed in the Miocene Climate optimum (MCo; 17-14.7 Ma), followed by the Middle Miocene Climate transition (MMCt;14.2-13.8 Ma;SHevNell et al., 2004;Hol-BourN et al., 2015). Global cooling events with temperature decreases in the range of 3-5°C have been dated to 13.8 Ma and 13.2 Ma (BöHMe et al., 2011, and literature cited therein). rich fossil plant assemblages and mammal faunas have been used to establish paleoclimatic models for this time interval (uteSCHer et al., 2007;BöHMe et al., 2011;BruCH et al., 2011;ivaNov et al., 2011). although the paleoclimatic concepts vary in certain details, there appears to be a consensus that the Serbian terrain was characterized by a humid, warm climate with high precipitation levels and predominantly evergreen vegetation during the time of the MCo. overall cooling and the seasonality of temperature and precipitation increased in the area during the times of the MMCt, and the vegetation gradually changed to a mixed mesophytic forest environment with more deciduous elements (ute SCHer et al., 2007;BruCH et al., 2011;ivaNov et al., 2011). However, cold winter temperatures are hypothesized to have only occurred from the Sarmatian s.s. onwards (uteSCHer et al., 2007;ivaNov et al., 2011). in the aquatic freshwater environment, Neu Bauer et al. (2015a) noted a first major faunal turn over in mollusks at the end of the MCo, however, their hypothesis was subsequently modified to a more gradual transitional model (NeuBauer K a t a r in a B r a d i ć -M i l i n o v i ć , Lj u p k o R u n d i ć & VVe r n e r S c h w a r z h a n s Fig. 7. The freshwatergobiesfrom Vračevićin the context ofthe composition ofthe "lost mid-Miocene freshwatergoby population"depicting the species and ranges ofthe genera Eleogobius, Klincigobius, Rhamphogobius, and Toxopyge. Arrows indicate assumed migration routes and provenances. derived fro m a co n te m p o ra ry M ed iterranea n/P aratethyan goby stock (Fig. 7]. It does n o t seem to be related to e ith e r an e a rlie r late Oligocene to early M iocene fre sh w a te r goby association k n o w n fro m central Europe (Reichenbacher, 2000; G ie rl et al., 2 0 13] o r to the late Miocene freshw ater goby stock th a t has been observed in Lake Pannon (Schvvarzhans, 2010 and lite ra tu re cited th e re in ] and U kraine (Bratishko et al., 2017], In addition, lt appears to have evolved at a tim e w hen the Paratethyan Sea had already been separated fro m the w o rld ocean (Fig. 8] and

A c k n o v v le d g e m e n ts
We thank Slavica Đajić, palynological expert of the Geological Survey of Serbia, for identifying and evaluating the palynomorphs discussed in this study. Her analysis