Stratigraphic and palaeogeographic significance of lacustrine molluscs from the Pliocene Viviparus beds in central Croatia

The mollusc fauna from the Pliocene Viviparus beds of Vukomeričke Gorice hills in central Croatia was investigated at four sites in the region of Kravarsko, S of Zagreb. The region represents a Pleistocene horst-anticline at the southern margin of the Sava depression. Sediments are dominated by clay, bearing some sand, gravel and lignite intercalations. The molluscs, comprising 11 gastropod and 2 bivalve species, seven of which (76.9%) are endemic to the region, prove that the studied deposits were derived from the ancient Lake Slavonia. The taxonomic revisions include the introductions of Viviparus kochanskyae n. sp. for specimens from Lake Slavonia previously identified as V. fuch­ si NEUMAYR, 1872 and Prososthenia? praeslavonica n. nom. replacing the primary homonym Hydrobia vitrella BRUSINA, 1897 non STEFANESCU, 1896. Recognized as an independent phase in the geodynamic evolution of the Pannonian Basin, the new regional stage Cernikian is introduced for the succession, defined by the complete depositional sequence of the Viviparus beds. Two stratigraphic horizons detected in the studied sites are constrained by the Lower Cernikian Viviparus kochanskyae and the Upper Cernikian Viviparus hoernesi zones and remain in good agreement with previous regional data. The historical timeline for Lake Slavonia is enabled through several zonal markers calibrated to the Geological Time Scale in the Dacian Basin. Accordingly, the Early Cernikian transgression dates to c. 4.3 Ma, the Late Cernikian transgression to c. 3.1 Ma, indicating strong alteration of the lacustrine depositional settings during the Pliocene, most likely related to changes in the regional climate. Interestingly, the second transgression of Lake Slavonia is marked by the evolution of strongly sculptured viviparid shells and coincides with the Pliocene Climate Optimum.


INTRODUCTION
The climatic and geodynamic settings during the Pliocene provided conditions facilitating extended lacustrine environments in southeastern Europe (NEUBAUER et al., 2015a, c).The resulting long-lived palaeo-lakes such as Lakes Slavonia, Metohia, Transylvania and Dacia were all characterized by explosive adaptive radiations of viviparid snails (HARZ-HAUSER & MANDIC, 2008;NEUBAUER et al., 2015a).This phenomenon allowed NEUMAYR & PAUL (1875) in their famous, pioneering study on Lake Slavonian molluscs to establish a regional biostratigraphy, enabling an excellent stratigraphic control of those deposits stretching over more than 600 km along the southern margin of the Pannonian Basin.
The present investigation deals with the corresponding mollusc record of Lake Slavonia (Figure 1).The samples originate from the region of Kravarsko, which is the type locality of several species described by BRUSINA (1874a, b, Figure 1: Map illustrating the recon structed extent of the Pliocene Lake Slavonia (light blue) adapted from NEUBAUER et al. (2015a); Viviparus beds (dark blue) are redrawn from the geological map of the Croatian Geological Survey M 1:300,000; Pan nonian basin infill (gray) is redrawn from the previous map and from the Yugoslavian geological map M 1:500,000; SRTM topographic mo del is the ArcGIS World Shaded Relief map by ESRI.White dots indicate stu died localities and the type localities of the Cernikian defined in the pre sent study.
By the end of the Middle Miocene, the Paratethys Sea retreated and the remaining brackish Lake Pannon gave rise to spectacular endemic mollusc radiation in the Late Miocene (MÜLLER et al., 1999;HARZHAUSER & MANDIC, 2008;NEUBAUER et al., 2015a, c). Isolation lasted up to 6.04 Ma when the connection with the Dacian Basin becomes established during the early Pontian (STOICA et al., 2013), followed by the migration of the endemic fauna into the Eastern Paratethys (STEVANOVIĆ et al.,1990).With the onset of the Pliocene, Lake Pannon was largely infilled by sediment due to the prograding river systems of the palaeo-Danube and palaeo-Tisza and became restricted in its ultimate phase to NE Croatia and N Serbia (MAGYAR et al., 1999(MAGYAR et al., , 2013;;UHRIN & SZTANÓ, 2012).During a new period of isolation from the Dacian Basin in the late Dacian, it became replaced by the freshwater environment of Lake Slavonia (STEVANOVIĆ et al.,1990;MARINESCU & PAPAIANO-POL, 1995).
The investigated region (Figure 1) represents the southern margin of the Sava depression, a NW-SE striking extensional structure filled by more than 5 km of predominantly siliciclastic Neogene deposits (TROSKOT-ČORBIĆ et al., 2009).The sedimentary infill of the Sava depression (Figure 1897(Figure , 1902)).Situated in central Croatia, in the close vicinity of Zagreb, it represents the western most extent of the palaeo-lake.Freshwater deposits alternate therein with alluvial series, providing an approximately 400 m thick Plio cene continental succession (GALOVIĆ, 1952).The series is usually referred to in the literature as the "Paludina beds" (KRSTIĆ, 2003;POPOV et al., 2004).Paludina FÉRUSSAC, 1812, however, is a junior synonym of Viviparus MON TFORT, 1810, which is why we use the term "Viviparus beds" in the present study.Note that this is only an informal lithostratigraphic unit according to the international stratigraphic code (SALVADOR, 1994).
The aim of the study is to investigate and document the taxonomic inventory of the region, to update the taxonomy of the identified species, and to evaluate the resulting biostratigraphic and palaeo biogeographic patterns for Lake Slavonia and the neighbouring palaeo-lakes.Additionally, the outdated Late Miocene to Pliocene stratigraphic nomenclature of the Sava depression sedimentary series is revised and a new stage name is introduced, constrained by the depositional duration of the Viviparus beds and Lake Slavonia, respectively.

SOUTHERN PANNONIAN BASIN AND SAVA DEPRESSION
The Pannonian back-arc basin is a large Neogene extensional structure located between the Alpine, Dinaride and Carpathian fold-and-thrust belts in central and SE Europe (SCHMID et al., 2008;USTASZEWSKI et al., 2014).Its formation is bound to the rapid Miocene roll-back of the Carpathian (and probably Dinaride) slab attached to the European continent, and to the Adriatic microplate, respectively (MATENCO & RADIVOJEVIĆ, 2013).The initiation of the synrift phase is marked by the first alluvial and lacustrine deposition in its southern domain dated to ~18 Ma (Early Miocene).Its marine ingression by the Central Paratethys clearly followed later at ~15 Ma in the Middle Miocene (ĆORIĆ et al., 2009;MANDIC et al., 2012) (Figure 2).In northeastern Croatia, the post-rift deposition had already begun at ~13.8 Ma in the late Badenian and continued throughout the middle-late Miocene (PAVELIĆ, 2001).The area of north Croatia experienced strong compressional uplifting in the Pliocene and Pleistocene that caused erosion and reworking of the Miocene deposits and exhumation of the pre-Miocene basement (PAVELIĆ, 2001).tion of Lake Slavonia.In the Sava depression, the Pannonian is four-fold, composed of the Radix cro atica, Congeria banatica, Paradacna abichi and Congeria rhomboidea beds (JENKO, 1944;LUČIĆ et al., 2001).Hitherto, the P. abichi and the C. rhom boidea beds were correlated with the Pontian Eastern Paratethys stage (STEVANOVIĆ, 1951;STE-VA NO VIĆ et al., 1990;LUČIĆ et al., 2001).However, such correlation is shown to be incorrect.In the Pannonian Basin, volcanic ash on top of the lower "Pontian" deposits in the vicinity of Tihany (central Hungary), correlates with the top of the P. abichi beds, revealing an 40 Ar/ 39 Ar calibration point of 7.95 Ma (WIJBRANS et al., 2007;MAGYAR & GEARY, 2012;SZTANÓ et al., 2013).Such an age significantly predates the Pontian interval, which is constrained in the northern Black Sea Basin to 6. 04-5.60 Ma (KRIJGSMAN et al., 2010).To avoid the pitfalls of erroneous correlations in the future and to stabilize the regional chronostratigraphic sche mes, the usage of units defined outside the respective geodynamic complex should be rejected.
Yet, the third depositional megacycle of the Sava depression (Figure 3), marked by the deposition of Figure 3: Revised regional stratigraphic scheme of the Sava Ba sin (modified after SAFTIĆ et al., 2003).Those authors place the synrift/postrift boundary at the transition of the middle to late Miocene.Yet, in the eastern Sava depression this boundary cor relates with the middle Badenian as documented by PAVELIĆ (2001).MATENCU & RADIVOJEVIĆ (2012) demonstrated that the synrift phase continues in some regions of the southern Panno nian Basin well into the Pannonian, whereas the postift phase may start already in the early Badenian.
3) shows three depositional megacycles separated by compressional phases dated to the late Middle Miocene, the Miocene-Pliocene transition and the early Pleistocene (SAFTIĆ et al., 2003).The first cycle comprises up to 2 km of Middle Miocene marine deposits of the Central Paratethys, the second cycle represents up to 2.5 km of Upper Miocene brackish water deposits of Lake Pannon, and the third cycle includes up to 0.9 m of freshwater deposits of the Pliocene Lake Slavonia (OŽEGOVIĆ, 1944;SAFTIĆ et al., 2003).Pleistocene to Holocene alluvial, marsh and aeolian deposits seal the succession.

REVISION OF THE STRATIGRAPHIC NOMENCLATURE AND THE NEW REGIONAL STAGE CERNIKIAN
In terms of regional stratigraphic nomenclature, the complete second megacycle of the Sava depression infill corresponds to the Pannonian stage (Figure 3).Its lower boundary corresponds to the formation of Lake Pannon, coinciding with the major extinction of Sarmatian marine species (Sarmatian-Pannonian extinction event of HARZHAUSER & PILLER, 2007).Its upper boundary is defined by the forma-the Viviparus beds during the Pliocene and Pleistocene, has also been correlated with the Dacian and/or Romanian regional stages of the Dacian Basin (JENKO, 1944;LUČIĆ et al., 2001;POPOV et al., 2004;MALVIĆ, 2012).However, due to tectonic inversion, Lake Slavonia represents a fully independent palaeogeographic unit from the early Pliocene, showing depositional dynamics different to those of the Dacian Basin (SAFTIĆ et al., 2003;SZTANÓ et al., 2013;STOICA et al., 2013;VAN BAAK et al., 2015).Considering the enormous thickness of the Viviparus beds along with their well-established stratigraphic subdivision (e.g., PENECKE, 1884;JENKO, 1944;OŽEGOVIĆ, 1944;TAKŠIĆ, 1954), and following the example from the Dacian Basin (ANDREESCU & PAPAIANOPOL, 1975;ANDREESCU, 1975;PAPAIANO-POL et al., 2003), we recognize a practical need for the introduction of a new and independent chronostratigraphic unit.
Thus, we herewith introduce the Cernikian new regional stage (Figure 2).The stage name derives from the village of Cernik near the boundary stratotype, as defined below (Figure 1 and 3).The stratigraphic content of the new regional stage corresponds to the Viviparus beds as defined by NEU-MAYR & PAUL (1875).Its duration equals their maximum depositional extent, i.e., it corresponds to the duration of Lake Slavonia.The stage is threefold as defined by its fossil content.Hence, the Lower Cernikian or Lower Viviparus beds include the V. neumayri and V. kochanskyae zones; the Middle Cernikian or Middle Viviparus beds comprise the V. bifarcinatus, V. stricturatus and V. nothus zones; and the Upper Cernikian or Upper Viviparus beds include the V. sturi, V. hoernesi, V. zelebori and V. vukotinovici zones.
The section NE of Cernik (Figure 1) is composed of marly clay with lignite seams bearing V. neumayri.It is superposed on the topmost Pannonian sand and is proposed as the boundary stratotype for the Cernikian (NEUMAYR & PAUL, 1875, p. 9, fig.4).The most complete succession occurring in the valley N of Malino (Figure 1) including Lower, Middle and Upper Viviparus beds, described in detail in NEUMAYR & PAUL (1875, p. 10-11, fig. 6), represents the type section ("holostratotype").A highly instructive, artificially outcropped section, showing a complete development of the Viviparus beds is described by OŽEGOVIĆ (1944) from the Gojlo anticline (Figure 1) E of Kutina in NE Croatia ("faciostratotype").There, the 900-m-thick Cernikian interval is composed largely of greenish clay and fine-sand with abundant viviparids.The 200-m-thick Lower Cernikian and the 600-m-thick Upper Cernikian interval contain 0.1 to 2-m-thick coal seams.

VUKOMERIČKE GORICE HORST-ANTICLINE
The investigated samples are from a 12 km² area large, 7.8 km long, and NW-SE striking region around Kravarsko.This village and municipality is located 30 km S of Zagreb in Croatia (Figure 1).The region is located on the NE flank of slightly elevated, forested countryside termed Vukomeričke Gorice, representing a large-scale horst-anticline composed of several smaller anticlines, uplifted in the Pleistocene along parallel longitudinal faults (PIKIJA, 1987a).Its surface is composed of the Viviparus beds, which are partly overlain by periglacial deposits at the northeastern margin (PIKIJA, 1987b).The basement, detected in wells at a depth of 863 m (Well Dubranec 2; GALOVIĆ, 1952), consists of Palaeozoic green quartz-chlorite schists and belongs to the Internal Dinaride Jadar-Kopaonik thrust sheet (SCHMID et al., 2008).It is directly overlain by Badenian biogene limestones.Upwards, the succession comprises Sarmatian marls and sandstones, Pannonian marls and Cernikian clays (Figure 3).
The Cernikian interval attains thicknesses of 200 to 450 m with inclinations of 2° to 12°.In the Kravarsko area, the Middle Cernikian was not discovered either by drilling or surface mapping (GALOVIĆ, 1952;GAGIĆ & SOKAČ, 1970;JURKOVIĆ, 1993).The Lower Cernikian, is represented here only by the V. kochanskyae zone, and is dominated by plastic clay, bearing some sand packages and up to 3.8 m thick coal seams consisting of reed-and wood-like plant material (STUR, 1863;FARKAŠ-VUKOTINOVIĆ, 1863;JURKOVIĆ, 1993;ŠEBEČIĆ, 2010).Above an indistinct unconformity, the Upper Cernikian shows an erosional contact with some faunal reworking.Sandy clays alternate and there are few lignite seams, and local coarse to fine grained gravel packages.The V. sturi, V. hoernesi and V. vukotinovici zones were detected in the Upper Cernikian.
The initial work on the mollusc fauna of the Vukomeričke Gorice hills was carried out by PILAR (1873) and BRUSINA (1874aBRUSINA ( , b, 1884BRUSINA ( , 1885BRUSINA ( , 1896BRUSINA ( , 1897BRUSINA ( , 1902)).KOCH (1917) provided the last census of the fauna recording 41 species altogether, although his list lacked the Middle Cernikian zonal markers.GAGIĆ & SOKAČ (1970) studied the ostracods from the drill cores.The faunal composition suggested a vegetated lake bottom in shallow sublittoral water-depths of 10 m or less, and a Pliocene to Pleistocene age for the Cernikian deposits.

LOCALITIES AND SAMPLES
From each locality one sample was analyzed, coded as Kra-I, VGK-39, VGK-38 and VGK-35 (Figure 1).Kra-I is located 1.73 km NW of the Holy Cross church in Kravarsko, SW of the houses termed Povoljnaki, at 192 m a.s.l., on the slope below the main road (45.595525°N 16.038053°E).The outcrop area is an active landslide laterally extending about 50 m.Except for a 3.4 m thick interval exposed at the northern limit of the landslide area, the bedding is largely disturbed.The former outcrop is dominated by a structure-less, grayish to yellowish clayey silt, with scattered plant remains.A 1.15 m thick unit of gray homogenous clay is intercalated in the lower part of the interval.The topmost 25% of this package displays fine-scale banding due to the intercalation of fine and medium grained sand.The sampled mollusc concentration occurs in the land-slide area, laterally to the outcrop, being strongly deformed and disjointed.It acted apparently as an inhomogeneity surface with the original stratigraphic position on top of the undisturbed interval (Figure 4).VGK-35 is located 2.7 km WSW of VGK-39, beside the path in the wood SWS of Novo Brdo at 165 m a.s.l.(45.582877°N 16.021478°E).The small outcrop exposes 1.6 m of yellowish macrofossil free sand in its lower part.A 0.8 m thick fining upward interval of sandy to clayey silt follows (with an erosive boundary) in the upper part of the section.The sample comes from the initial 10 cm of the latter inter-val bearing poorly preserved, non-oriented mollusc shells suspended in a sandy silt matrix (Figure 4).

Taxonomy, palaeoecology and stratigraphy
The taxonomic revision provides several updates for the fauna (Table 1).Vi viparus kochanskyae is introduced as a new species for the zonal marker of the Lower Cernikian, a taxon formerly identified as Viviparus fuchsi (NEU-MAYR, 1872), which, however, is restricted to the Pannonian Basin.Three species, Microcolpia friedeli, Prosost henia?slavonica and Potomida seljani are newly combined in agreement with modern systematics (see taxonomy below).The cross-checking of the literature allowed a precise stratigraphic and palaeo biogeographic evaluation of the record (Tables 2 to 3).Except for Litho glyphus decipiens, Bithynia vukoti novici and Theodoxus semiplicatus, all other taxa are approved and appear to be restricted to Lake Slavonia (Table 3).
Altogether, the samples contain 13 lacustrine species, comprising 2 bivalve and 11 gastropod species (Table 1).As expected for the Viviparus beds, viviparids are the most diverse (4 species), followed by melanopsids and hydrobiids (2 species each).Further families (valvatids, ner-    (1875) and PENECKE (1884), the Lake Slavonia viviparid gastropod zones are defined here by the first appearance of the namegiving tax on.Except for V. neumayri and V. stricturatus, all are confined to their respective zones.Horizons identified in the studied region are marked in bold.
itids, bithyniids, unionids and sphaeriids) are represented by only one species each.
The highest number of species ( 10) is recorded from VGK-39, and they are also the best preserved.Material from sample Kra-I exhibits limonite colouring and partial leach-ing and contains a smaller number of species ( 6), all present in the previous sample.The difference in composition is probably only a taphonomic feature.This is supported by the presence of V. kochanskyae in both samples, which is a zonal marker restricted to the upper part of the Lower Cernikian.
In sample VGK-39, the melanopsid Microcolpia friedeli is the most frequent species, followed by the hydrobiid Prososthenia?slavonica.Melanopsids are generalists occurring in lakes and rivers, tolerating even slightly brackish conditions (GLAUBRECHT, 1996;BANDEL, 2000).Hydrobiids are present in different types of environments, and are usually well adapted to littoral mud flat settings (GLÖER, 2002;NEUBAUER et al., 2013a, b).Valvata piscinalis, which may represent an ecological counterpart of V. subcarinata, prefers fresh-and hard-water lake settings with a rich vegetation cover (ØKLAND, 1990).Theodoxus danubialis, as a potential counterpart of T. semiplica tus, is most abundant in fluvial environments but is also found in lakes (JURIŠIĆ-POLŠAK, 1979;WELTER-SCHULTES, 2012).Bythinia is a generalist, living in stagnant and moderately running waters on detritus-rich substrates (GLÖER, 2002).Viviparids are pure freshwater dwellers (WELTER-SCHULTES, 2012).Some European species prefer rivers, others settle in lakes.In Lake Geneva, they are highly abundant in the shallow, littoral zone (GLÖER, 2002).With respect to the ecological requirements of the mollusc species, from the dominantly muddy sediment and the lignites, a calm, littoral setting of a freshwater lake can be inferred for the samples, which is in agreement with previous ostracod data (GAGIĆ & SOKAČ, 1970).
Due to the generally poor preservation, the sample from Novo brdo (VGK-35) revealed only two species (Table 1), both of which are absent in Kravarsko.Viviparus hoernesi is a zonal marker of the Upper Cernikian, Melan opsis clavigera is restricted to the V. hoernesi and V. zele bori zones (PENECKE, 1884).This suggests a stratigraphic position within the middle Upper Cernikian.V. dezmani anus, identified as a single species from the Burdelj wood (VGK-38), could be of the same age.It has a long stratigraphic range (PENECKE, 1884), concurring among others also with V. hoernesi.This is in agreement with the results of previous investigators reporting both viviparid species as constituents of the Upper Cernikian fauna of the Vukomeričke Gorice hills (GALOVIĆ, 1952;GAGIĆ & SOKAČ, 1970).

Calibration of the Cernikian to the GTS and the Pliocene Climate Optimum
Although representing an isolated lake, at least temporary southward outflow from the Pannonian Basin existed according to PAPAIANOPOL & MARINESCU (1995), allowing some species to migrate to the Dacian Basin (Figure 5  and 6).This facilitates a rough calibration of the Cernikian biostratigraphy to the Dacian and Romanian substages based on shared Viviparus zonal markers (Figure 6).This allows an indirect correlation to the Geological Time Scale (GTS) based on the magnetostratigraphic age model for the Pliocene of the Dacian Basin of VAN BAAK et al. (2015).This model calibrates the Upper Dacian (Parscovian) base to 4.5 Ma, the  VAN BAAK et al. (2015).Calibration of Viviparus biozones is based mainly on LUBENESCU & LUBENESCU (2008) and own data (see text).Stand ard chronostratigraphy follows HILGEN et al. (2012).Note the indicated position of the two stratigraphic levels identified in the studied sites and the one mil lion year gap between them.This agrees with previ ously published results showing the absence of mid dle Viviparus beds in western Lake Slavonia.This implies a 1 myr long retreat of the Lake Slavonia east wards with subsequent shortterm flooding during the Pliocene Climate Optimum.
Lower Romanian (Sienisian) base to 4.2 Ma, the Middle Romanian (Pelendavian) base to 3.6 Ma and the Upper Romanian (Valachian) base to 3.1 Ma.
The calibration presented in Figure 5 is based on a literature review: LUBENESCU & LUBENESCU (2008) showed V. stricturatus and V. sturi to be restricted to the Pelendavian of the Dacian Basin.ANDREESCU et al. ( 2013) presented V. bifarcinatus as a zonal marker of the same substage.VAN BAAK et al. (2015) used the first appearance of V. stricturatus as a marker of the base of the Pelendavian.LUBENESCU & LUBENESCU (2008) reported V. pilari and V. rudis as being restricted to the Valachian.The latter species are restricted in the Pannonian Basin to the V. hoer nesi zone (PENECKE, 1884).The correlation of the Cernikian base with the base of the Parscovian follows PAPA-IANOPOL et al. (2003).
According to the presented correlation, the Cernikian spans the interval from 4.5 Ma to 2.0 Ma.The lower boundary of the Middle Cernikian is correlated to 4.2 Ma, the base of the Upper Cernikian corresponds to 3.3 Ma, approximately coinciding with the start of the Pliocene Climate Optimum (PCO).The period between 4.3 and 2.7 Ma represents a general warm phase during the Pliocene, culminating between 3.3 and 2.9 Ma.At that time, polar temperatures increased by up to 10°C, the ice caps melted rapidly and global sea level was about 25 m higher than today (FOLLAND et al., 1990;RAYMO et al., 1996;FEDOROV et al., 2013;WILLEIT et al., 2013).Interestingly, the increase of shell sculpture in lineages of the Lake Slavonia viviparids paralells the warming trend during the PCO (Figure 6).Thereafter, generally weaker sculptured species of the V. vukoti novici zone followed (NEUMAYR & PAUL, 1875).

Implications for the history of Lake Slavonia
The biostratigraphic framework described above allows correlation of the studied sites with the Lower and Upper Cernikian (Figure 5).This fully agrees with previous results by GALOVIĆ (1952) and GAGIĆ & SOKAČ (1970) confirming that the Middle Cernikian is missing in the Vukomeričke Gorice hills.Considering that the area represents the west-ernmost extent of Lake Slavonia and in respect to the general eastward fluvial flow direction in the Pannonian Basin, important implications for the history of Lake Slavonia can be drawn.
In particular, the distribution pattern in the mollusc assemblages proved that two main flooding events of Lake Slavonia occurred in the investigated area, correlating with the Viviparus kochansyki zone and the Viviparus hoernesi zone.The first flooding coincided with the start of relatively warm climate conditions in the region (Figure 6).Lake Slavonia had already at c. 4.3 Ma a distinctly larger surface than Lake Pannon in its final phase in the early Pliocene at c. 4.5 Ma (MAGYAR et al., 1999) (Figure 1).In contrast, the Middle Cernikian seems to represent a generally arid climate phase in the region, resulting in the retreat of Lake Slavonia from the Vukomeričke Gorice hills.The second ingression at c. 3.1 Ma coincided with the PCO (FEDOROV et al., 2013;WILLEIT et al., 2013), followed apparently by the reestablishment of humid conditions and a further increase in the size of Lake Slavonia (Figure 5).
MARINESCU & PAPAIANOPOL (1995) reconstructed Lake Slavonia rather as a system of lakes connected by rivers.Such a scenario was certainly possible for the time of the Middle Cernikian arid spell reflected by a more than 1 Ma long interruption of lacustrine deposition in the Vukomeričke Gorice hills.The renewed rise of the lake indicates that Lake Slavonia was not simply filled from the west to the east like the Miocene Lake Pannon (MAGYAR et al., 2013).Instead, active subsidence in the southern Pannonian Basin provided accommodation space for terrestrial input and allowed the persistent existence of lacustrine conditions throughout the Pliocene and the earliest Pleistocene (SAFTIĆ et al., 2003).Previous authors (GALOVIĆ, 1952;GAGIĆ & SOKAČ, 1970) indicated the presence of the zonal marker V. vukotinovici in the Vukomeričke Gorice hills with FOD at ~2.5 Ma.Therefore, the tectonic inversion could not have started prior to that time.
A connection to the Dacian Basin as suggested by MA-RINESCU & PAPAIANOPOL (1995) is corroborated by the high similarities between the mollusc faunas.Following the  et al. (2015a) indicating lakes from where the species observed at the Vukomeričke Gorice hills were previously reported.Note that most of these occurrences are proven to be erroneous after the present revision (see Table 3).
synopsis of NEUBAUER et al. (2015a), 50 of the 163 species (30.7%) recorded for Lake Slavonia are also known from Lake Dacia (Figure 6).It is therefore likely that temporary one-way connections existed through outflow from the Pannonian Basin (MARINESCU & PAPAIANOPOL, 1995).

CONCLUSION
The Pliocene Viviparus beds of the Vukomeričke Gorice hills in central Croatia represent the topmost sequence-stratigraphic megacycle of the Sava depression sedimentary infill.This interval represents an independent phase of the geodynamic evolution of the Pannonian Basin.For that reason, a new regional stage termed the Cernikian is introduced here, defined by the depositional cycle comprising the Viviparus beds.The cycle is linked to the development of a freshwater lake termed Lake Slavonia.Its deposits transgressively overlie Pannonian brackish-water deposits of Lake Pannon, previously referred to the Pontian.The Pontian stage, however, is clearly older and was defined in a completely different geodynamic area.Therefore, regional stages such as the Pontian, Dacian and Romanian should only be used in the respective type areas and must not be applied to the southern Pannonian Basin.
The fauna shows an excellent match with the Viviparus beds of NE Croatia proving it as a fully integrated constituent of the long-lived Lake Slavonia.The biostratigraphy of Lake Slavonia is well established, based on the rapid endemic evolution of viviparid gastropods.Two stratigraphic horizons detected in the studied sites support previous regional subdivisons.These are the Lower Cernikian Viviparus kochanskyae zone and the Upper Cernikian Viviparus hoer nesi zone.The lack of the Middle Cernikian in the Vukomeričke Gorice hills indicates strong alteration of the lacustrine depositional settings in the Pliocene of the southern Pannonian Basin.Considering that the subsidence was constant within the respective megacycle, the inferred pattern is best explained by the Middle Cernikian arid spell reflected by back-stepping of the lake.
The timing of the latter event is enabled through several zonal markers calibrated to the Geological Time Scale in the Dacian Basin, indicating where some species of Lake Slavonia migrated via rivers.Accordingly, the Early Cernikian lacustrine transgression dates to c. 4.3 Ma and the base of the Late Cernikian to c. 3.1 Ma, proving a more than 1 Ma long depositional hiatus for the region.Interestingly, the second lacustrine transgression of Lake Slavonia is marked by the evolution of strongly sculptured viviparid shells and coincides exactly with the Pliocene Climate Optimum.

SYSTEMATIC PALAEONTOLOGY
Gastropod systematics follows BOUCHET & ROCROI (2005) and the WoRMS database.Systematics of the bivalves follows BOUCHET & ROCROI (2010) and GRAF & CUMMING (2007,2014).Description: Glossy, trochiform shell, slightly wider than high (W/H=0.92),with 4.5 rounded whorls rapidly and continuously increasing in diameter, delineated by deep sutures.Last whorl attains 87% of total shell height.Aperture is subcircular,weakly oblique, slightly angulated adapically at the contact with the last whorl.Peristome is sharply edged.Umbilicus narrow and deep.Shell covered with fine, nonprojecting growth lines and fine axial undulations marking the growth stops.Protoconch low trochiform, attaining little more than one whorl, showing fine spiral microsculpture typical for valvatids.For a long time, this species was considered conspecific with specimens from the Pannonian of Moosbrunn in the Vienna Basin identified by HÖRNES (1856) as Valvata piscinalis MÜLLER, 1774(NEUMAYR, 1869;BRUSINA, 1874a,b;NEUMAYR & PAUL, 1875).Even after BRU SINA (1878) introduced V. subcarinata as a new species restricted to Lake Slavonia sediments, this error was carried forward by WENZ (1928).PAPP (1953, pl. 5, fig.2) was the first to recognize this mistake and related the distinctly older Austrian occurrence with the Pannonian species Valvata obtusaeformis LÖRENTHEY, 1906 stating its different outline due to a much slower increase of the spire's diameter.After BANDEL (2010), the latter species might be related to the valvatoid hydrobiid genus Jekeliella BANDEL, 2010.

Remarks
The Recent Valvata piscinalis MÜLLER, 1774 differs in its lower spire, the wider umbilicus and the missing posterior notch at the aperture, which is well-developed in specimens from the type locality and the present material from Kravarsko.BRUSINA (1874a, b) mentioned "two to three" specimens out of 35 from Kravarsko that develop a sharp median spiral keel, restricted to the early whorls.This is not developed in our material.Though BRUSINA (1897) illustrated just those keeled specimens as representatives of V. subcarinata, he still considered the more frequent nonkeeled morphotype as conspecific.We follow this approach and treat both morphologies as belonging to the same species.
PENECKE (1884), in contrast, used a different concept of V. subcarinata for his material.He restricted it to the keeled morphotype found in the LVB at Malino and Čaplja.For the keeled specimens from the UVB at Repušnica and Čaplja, he introduced V. hoernesi as new species, which later was considered a juvenile specimen of V. subcarinata by BRUSINA (1897).Consequently, he continued to identify the non-keeled morphologies with the Recent Valvata piscinalis, claiming its presence in all stratigraphic horizons of Lake Slavonia.He erroneously synonymized V. sulekiana BRUSINA, 1874 with V. piscinalis, which differs clearly in its strongly flattened spire.
The stratigraphically older specimens from the Late Miocene Metohia Basin in Kosovo, erroneously identified as V. subcarinata by MILOŠEVIĆ (1984), differ in a narrower spire and smaller aperture.Specimens from the Dacian of the Braşov Basin, referred to V. subcarinata by JEKELIUS (1932), expose several weak to prominent spiral keels and thus represent a different species.
Description: Solid shell, consisting of 2.75 whorls.Spire consists of two flattened whorls (always eroded in the present material).Depending on the shell's growth angle, the spire may be distinct or be fully covered by the last whorl.Last whorl increases strongly in diameter, producing an oval shape in outline.Aperture is semicircular, slightly inclined toward the columella, with sharp lateral margin.Callus pad is well demarcated, slightly concave, smooth, bearing very fine denticles at its adapertural edge.Colouring is dominantly expressed by black, axial zig-zag and wavy bands.In a few specimens the bands are fused, so that only a few lunate spots remain white.

Remarks: T. semiplicatus NEUMAYR in HERBICH &
NEUMAYR, 1875 from Vârghiş and Araci (Dacian, Braşov Basin, W Romania) was made available through a lapsus calami for T. semidentatus SANDBERGER, 1875 (see footnote in HERBICH & NEUMAYR, 1875, p. 413).The latter species had been introduced for a misidentified species from the Middle Miocene of Ribarić in the Drniš Basin, SE Croatia.Not realizing that the Middle Miocene species is distinct from the Pliocene one, HERBICH & NEUMAYR (1875) mentioned "T.semiplicatus" (instead of T. semidenta tus) also from the Dacian of the Braşov Basin.As they explicitly referred the misspelled species name to a different specimen, both names are valid.BRUSINA (1884) was the first to recognize that these two names refer to different species.
Although citing 57 syntypes from Čaplja near Podvinje in Slavonia (NE Croatia), BRUSINA (1874a) did not provide any description or illustration of his new subspecies T. danubialis sagittiferus.This species-group name is therefore a nomen nudum, a fact first recognized by JURIŠIĆ-POL-ŠAK (1979).Nevertheless, NEUMAYR & PAUL ( 1875) also foun d it at Čaplja, in beds belonging to the V. hoernesi zone, and accepted it as an available name.BRUSINA (1884) elevated the name to the species rank and provided a morphological description and therefore made it available.
Description: Slender shell, consisting of 5 convex whorls.Shell width attains about 60% of total height; suture not very deep but distinct.Last whorl attains 70% of total shell height.The junction between the whorls is irregular, slightly gaping.Protoconch is eroded, apex is blunt.Whorls increase more strongly in height than diameter, resulting in a drop-shaped shell outline.Aperture is oval to slightly dropshaped, with a weak posterior notch.Peristome is sharp; umbilicus is narrow and slit-like.Shell surface is glossy, bearing numerous fine, weakly but irregularly undulated spiral grooves; crossed by growth lines they partially produce a fine reticulate pattern.
Remarks: When describing the species, BRUSINA (1874a) had only a single specimen from Cernik (Sv.Linart) N of Nova Gradiška at hand.The specimen, with a height of 30 mm and a width of 20 mm, represents a holotype by monotypy (ICZN Art.73.1.2) and is stored in the NHM Zagreb (Inv. No. 3215-861;MILAN et al., 1974).Following the detailed geological description of the area by NEUMAYR & PAUL (1875), the deposits at the type locality may be ascribed to the V. neumayri zone.
Viviparus rudolphi PENECKE, 1884 from the V. ko chanskyae zone of Malino was previously recognized by BRU SINA (1897) as a synonym of V. aulacophorus.WENZ (1926) erroneously synonymized the nomen nudum "V.anthra cophilus" as given in NEUMAYR & PAUL (1875) with V. aulacophorus.He apparently overlooked the correction note in NEUMAYR & PAUL (1875, p. 106), where they clearly indicate it as an error pro V. leiostracus.Following ICZN Art.32.4 and 32.5, the name anthracophilus clearly represents an inadvertent error and is thus unavailable.
The specimen given as "Viviparus neumayri trans V. suessi" in NEUMAYR & PAUL (1875, pl. 4, fig. 4) from the UVB of Novska seems to show a very fine spiral sculpture too, but has a much lower spire.Viviparus pauli BRUSINA, 1874 and V. dautzenbergi BRUSINA, 1902 are both larger than the present species and develop a much more prominent spiral sculpture (see also BRUSINA, 1897).Viviparus pauli has been listed from Kravarsko by BRUSINA (1874a, b) but could not be detected in the course of our investigation.

Viviparus dezmanianus
Descriptions: Solid shell, large, broadly drop-shaped, comprising 5.25 whorls; width attains about 65% of height.Protoconch is not preserved.First three whorls are weakly convex and separated by shallow sutures, producing a point ed, conical apex.Thereafter whorls expand more strongly in height than width, resulting in an overall dropshaped outline.From the third whorl onwards, whorls expose markedly stepped outlines with flanks sub-parallel to the axis, a narrow sutural ramp and incised, slightly gaping sutures.Angulation between ramp and flank starts rounded, but becomes progressively more strongly angled and sharper.Ramps dip by 30° to 60°.Flanks are initially slightly convex and then straight, up to slightly concave on the last whorl; a central spiral furrow emerges on the last two whorls.A second angulation is present at the transition between whorl flank and base; it becomes visible only on the last two whorls.Base of the last whorl is weakly convex.Last whorl attains about 80% of the total shell height.Aperture is fragmented, but obviously broadly drop-shaped, posteriorly slightly narrowed.Peristome is sharp in its preserved columellar part.Umbilicus is closed.Growth lines are distinct, opisthocline.
Remarks: BRUSINA (1874a) introduced this species including a specimen of the syntype series of V. rudis NEU-MAYR, 1869.It is not clear from the discussion whether he considered V. dezmanianus as a replacement name of NEU-MAYR's specimen or simply wanted to include it in the new species.Therefore, all specimens studied by BRUSINA (1874a) and the single specimen from NEUMAYR (1869) are syntypes of V. dezmanianus.The specification of a "holotype" by MILAN et al. (1974), referring to the specimen from Kovačevac (Coll.NHM Zagreb Inv.No. 4272-1912/1) that was illustrated in BRUSINA (1874a, b), is incorrect.To settle this issue we designate the same specimen herewith as a lectotype.
We follow NEUMAYR & PAUL (1875) and WENZ (1926) and consider V. complanatus BRUSINA, 1874 as conspecific with V. dezmanianus.Its type series comprises 127 specimens from Čaplja.It attains only 75% of the height of the typical morphotype and the keels are less pronounced, resulting in rather straight-sided whorl flanks (as in our specimens).These minor variations are considered to be within the range of intraspecific variability.
In their revision of the viviparids from the Pliocene of the Dacian Basin, LUBENESCU & ZAZULEAC (1985) rejected the presence of V. dezmanianus in Lake Dacia.They treated the identifications of COBĂLCESCU (1883) and WENZ (1942) as V. pseudo dezmanianus LUBENESCU & ZAZULEAC, 1985, whereas the specimens from the Sienisian by PORUMBARU (1881), FONTANNES (1887) and STEFANESCU (1896) were referred to V. dezmanianus dac icus LUBENESCU & ZAZULEAC, 1985.As noticed by NEUBAUER et al. (2014a), the latter taxon is a junior synonym of V. dezmanianus turbureensis FONTANNES, 1887.Whether or not V. dezmanianus turbureensis is really related to V. dezmanianus needs a more detailed assessment of the type material.
According to TABOYAKOVA (1964), the record of V. dezmanianus from the late Pliocene to Pleistocene of the Rioni Bay in Georgia (e.g., WENZ, 1926) actually represents Viviparus nataliae MIKHAYLOVSKIY, 1913.The species is, however, still listed from that region by ANISTRATENKO & GOZHIK (1995).A more thorough taxonomic revision of those records is required to confirm or reject this claim.
Description: Solid, glossy shell, conical, with 5 whorls, with the last whorl attaining about 80% of the total height.Protoconch is not preserved.Apex is blunt.On the second whorl a prominent angulation emerges, forming a straight, near horizontal subsutural ramp.Angulation successively passes into a marked, sharp keel.A second sharp keel bearing irregular, elongated nodes emerge at the transition between whorl flank and base and are visible only on the last whorl.Whorl flank between keels is regularly concave.Below the lower keel, 2 weak and thin keels cover the base of the last whorl.Base is straight.Aperture is not preserved but apparently sub-oval; umbilicus is completely covered.

Remarks:
The type series includes a large number of specimens from the Bukovica valley N of Novska (as are all the illustrated specimens), Repušnica and Gradiška.We designate herewith the specimen illustrated in NEUMAYR (1869, pl.14, fig.14), stored in the collection of the GBA (Inv.No. 1869/001/0055), as the lectotype.The type stratum in Bukovica belongs to the V. hoernesi zone, which the species is restricted to.
NEUMAYR in NEUMAYR & PAUL (1875) separated the specimen of NEUMAYR (1869) illustrated on Pl. 14, fig.13 as the new species V. ornata, based on the absence of nodes on the keels.PENECKE (1884) stated that these two species rather form a morphological continuum and a distinction is possible only between extreme morphotypes, which we do not follow.WENZ (1928) also lists the species from Craiova in the Dacian Basin, which needs a careful re-examination.LUBENESCU & LUBENESCU (2008) did not list this species in their comparison between Dacian and Pannonian basin molluscs.
Diagnosis: Broadly ovoid, solid shell of moderate size comprising 4-5 whorls, which expand more rapidly in height than diameter, with flanks initially convex, then flattened on the last two whorls.

5.16-17).
Description: Smooth, solid shell, broadly ovoid, with 4.75 whorls and narrow umbilicus.Shell width attains about 70% of its height.Protoconch not preserved in the present material.Whorls expand rapidly in height and diameter, with the last one attaining c. 75-80% of total height.Early whorls slightly convex, not stepped, separated by distinct but shallow suture.Flanks of the last two whorls flattened, passing into marked convexity below.Base is straight, inclined by about 45°.The latter is not fully preserved in our material; appears to be drop-shaped.Fine growth lines cover the shell.

Remarks:
The alleged presence of "Viviparus fuchsi" in the Viviparus beds of Croatia traces back to a series of misidentifications and nomenclatural mistakes.It started with a misidentification of NEUMAYR (1869), who mentioned "Vivipara concinna" from Nova Gradiška in NE Croatia, apparently referring to the identification and illustrations from HÖRNES (1856, p. 581, pl. 47, fig. 17).That author, however, had described a much older species from the middle Pannonian of Moosbrunn in the Vienna Basin.Despite superficial similarities, the single Slavonian specimen differs in the less stepped spire and the characteristically flattened whorl flanks passing into the marked convexity towards the base.Beyond that, neither of these species is Viviparus concinnus (SOWERBY, 1812), which is yet another species from the Paleogene of southern England.Recognizing this, NEUMAYR (1872) introduced the new name Viviparus fuchsi in a short note on the Viviparus beds, yet explicitly referring it to "V. concinna HÖRNES non SOW.".Despite his clear intention to introduce the name for the Slavonian species, V. fuchsi is still a replacement name for HÖRNES' misidentified specimens from Moosbrunn and not for the Slavonian species.
Obviously unaware of NEUMAYR's (1872) new name, SANDBERGER (1875) introduced "Paludina loxostoma" as replacement name for the species described by HÖRNES (1856).Although SANDBERGER ( 1875) also gives NEU-MAYR's record from the Viviparus beds in the synonymy list and mentions its occurrence in Nova Gradiška, it is entirely clear from the discussion that P. loxostoma was intended solely as a replacement for HÖRNES' material.He even listed the record of Viviparus fuchsi by BRUSINA (1874a, b) in the synonymy list, but, for whatever reason, did not consider it a valid name.Paludina loxostoma SANDBERGER, 1875 is therefore an objective junior synonym of Viviparus fuchsi NEUMAYR, 1872.It was later also considered synonymous by NEUMAYR & PAUL (1875) and WENZ (1928).
Based on illustrations of NEUMAYR & PAUL (1875), PAPP (1953) was the first to recognize the differences between the Pannonian and Slavonian species, but wrongly concluded that V. fuchsi is restricted to the Viviparus beds and V. loxos tomus is the correct name of the Pannonian species.Therefore, V. fuchsi was not mentioned from the Pannonian Basin by later authors (e.g., STRAUSZ, 1942;BARTHA, 1977;STEVA-NOVIĆ et al., 1990;HARZHAUSER & BINDER, 2004).
In summary, V. fuchsi NEUMAYR, 1872 and V. loxos tomus (SANDBERGER, 1875) refer to the same species from the Late Miocene of the Pannonian Basin, whereas the Slavonian species, usually referred to as "Viviparus fuchsi", actually has no name.Therefore, we introduce Viviparus ko chanskyae as a new species.Consequently, also the former "Viviparus fuchsi zone" has to be re-named the "Viviparus kochanskyae zone".
"Viviparus fuchsi" from the Late Miocene Lake Bresse-Valence in SE France originates from a misidentification by DELAFOND & DEPÉRET (1893).The French specimens have well-rounded, convex whorls and correspond well to Viviparus dresseli (TOURNOUËR, 1875), described from the surroundings of Lyon, a species they give in the synonymy list of V. fuchsi.Specimens of "Viviparus fuchsi" identified from the Akchagylian (Late Pliocene) of the Syzran region in western Samara/Russia by PAVLOV (1925) and from the Pontian of the Danube delta region in SE Ukraine by GOZHIK (2002) and GOZHIK & DATSENKO (2007) have convex whorls instead of the typically flattened ones and represent other, yet undetermined species.
Viviparus kochanskyae seems to be absent in the Dacian Basin.It is not listed (as V. fuchsi) in the monograph on its viviparid snails by LUBENESCU & ZAZULEAC (1985).The Pontian record at Ploieşti by WENZ (1928) dates back to a list of PILIDE (1877), reproduced also by STEFA-NESCU (1897, p. 61).Viviparus fuchsi identified by BERE-GOV (1940) from the Maeotian and Dacian of Bulgaria was shown by LUBENESCU & ZAZULEAC (1985) to represent V. incertus sensu MACAROVICI, 1940.The latter species name was recently recognized to be a primary homonym of V. incertus FUCHS, 1877 by NEUBAUER et al. (2014a), who introduced V. wesselinghi as a replacement name.
JEKELIUS (1932) reported V. fuchsi species from Dacian deposits of the Galat brook near Aita Seacă and Ebhát határ near Hăghig in the Braşov basin, but without providing any illustrations or description.This record still needs to be verified.
The alleged lineage leading from Viviparus fuchsi to V. leiostracus in the Pliocene of Kos as described by NEU-MAYR (1880a) is based on misidentifications of V. calverti (WILLMANN, 1981, p. 151).The record of V. fuchsi from the Plio-Pleistocene of Patras, Greece, by OPPENHEIM (1894, p. 820), who did not provide description or illustrations, needs re-examination.

Order unassigned
Descriptions: Solid shell with slender to bulky conical, coeloconoid to ovoid outline and up to 9 whorls.Shell width attains about 50% of height.Whorls are separated by narrow, irregular sutures.Protoconch unknown.Sculpture starts on the second teleoconch whorl, comprising about 8 slightly prosocline axial ribs, extending across entire whorl height.Number of ribs is roughly constant throughout ontogeny -ribs increase constantly in strength and are more or less continuous on successive whorls.On the last whorls, the ribs bear weak nodes near the upper suture.Nodes become successively stronger, producing a markedly stepped shell outline for the last 3 whorls.Rib portions above and below nodes are concave.On the last 2-3 whorls, nodes are laterally connected via weak, concave keels.On the last whorl, ribs bear an additional elongate axial convexity marking the angulation between whorl flank and the straight base.In one specimen, each rib bears two nodes; in two other specimens, no nodes are developed at all.The last whorl attains about two thirds of the total shell height.The aperture is slender, elongated and has a thickened callus pad; it lacks a columellar fold.Peristome and siphonal canal are not fully preserved.Fine growth lines are visible at the exterior surface of the shell.
Remarks: BRUSINA ( 1897) introduced the new subspecies Melanopsis clavigera cesticillus for a specimen from Kozarica near Novska, but did not provide a description or discussion.From the illustrations he provided, it seems he based the distinction on the absence of ribs and nodes on the last two whorls.A specimen of M. clavigera cesticillus from the same locality illustrated in BRUSINA (1902) shows a prominent keel, bearing irregular, bulbous knobs.As we are currently not aware of any morphotype representing a morphological transition to the typical M. clavigera, a taxonomic separation appears reasonable.
The record of Melanopsis clavigera by OPPENHEIM (1891) from the early Pliocene of Megara in Greece is clearly a misidentification.The Greek species is much more gracile and bears finer and sharper ribs with three rows of small nodes.Due to its weak spiral keel it does not show the stepped   1890), which lacks an illustration, can be ruled out as being conspecific with the present species.
Description: Glossy, slender shell, elongate, with up to 9 whorls, and width attaining about 58% of height.Whorls are weakly convex to straight in cross-section; sutures are shallow; the resulting outline is almost perfectly conical.Shell base is slightly concave.Last whorl attains 55-60% of the total shell height.Some specimens with convex whorls develop weak, slender, irregularly spaced, opisthocyrt ribs on the last 3-4 whorls, with the point of maximum convexity in the middle.Ribs on the last whorl are sigmoidal, parallel with the growth lines.Aperture is oval, with moderately thickened callus.Colouring occasionally present as yellow to orange quadratic spots, arranged in a loose chequer-board like pattern.
Remarks: As already stated in BRUSINA (1885), this species might be closely related to Microcolpia acicularis (FÉRUSSAC, 1823), which is the type species of Microcol pia BOURGUIGNAT, 1884.The original description by BRUSINA (1885) was a rectification of erroneous identifications of specimens from Kravarsko and Podvornica with M. acicularis by BRUSINA (1874a, b).BRUSINA (1897) provided an excellent illustration of one complete specimen from the Viviparus beds of Podvornica, which was designated as a neotype by MILAN et al. (1974) (Coll. NHM Zagreb Inv. No. 2998-664).However, this designation is insufficient according to ICZN Art.75.3.It is entirely unclear whether the original type material of BRUSINA (1885) has been lost or was later illustrated by BRUSINA (1897).Therefore, no type exists at present.
The exact geographic position of the Podvornica locality is uncertain.MILAN et al. (1974) indicated it to be ESE of Kutina, while JURIŠIĆ-POLŠAK (1979) positioned it N of Kravarsko.Its actual position could not be verified from additional literature.
The partly enormous intraspecific variation of Microcol pia species has recently been demonstrated by morphometric analysis for a Late Pleistocene to Holocene Microcolpia species flock from the Peţea thermal spring in Romania (NEU-BAUER et al., 2014b).Melanopsis astathmeta BRUSINA, 1897 from the LVB of Novska (=M.decollata sensu PE-NECKE, 1884 non STOLICZKA, 1862) is very similar to the non-ribbed morphotype of M. friedeli.It is slightly broader, has a larger last whorl and a more expanded aperture (cf.BRUSINA, 1897).Nevertheless, it is clearly a specimen of Microcolpia.Melanopsis sandbergeri NEUMAYR, 1869 from the LVB (?) of Repušnica has a bulkier last whorl and a distinct fasciole on the neck.M. recurrens NEUMAYR in NEU-MAYR & PAUL, 1875 (= M. decollata sensu NEUMAYR, 1869 non STOLICZKA, 1862) from Repušnica differs in its slightly stepped whorls with deeper sutures.
The identification of Melanopsis cf.friedeli from the Portaferrian (latest Pannonian) of Beočin (N Serbia) by KOCH (1902) has not recently been confirmed (STE VA NO-VIĆ et al., 1990) and remains doubtful.The record by PANĂ (2003) from the Sienisian of Valea Fântânei in the Dacian Basin is a misidentification.The illustrated specimens are shorter, have higher apical angles and more convex outlines.
Distribution: Lake Slavonia deposits in central Croatia at Podvornica, Kravarsko and Prvonožina; occurrences in the LVB of northern Serbia (Krivci/Sremski Karlovci) could not been approved and need careful re-examination.Material: VGK-39 (3 specimens from sample no.30) and Kra-I (2 specimens from sample no. 1, and 1 specimen from sample no.21).

Order
Dimensions: Height x width -12.6 x 8 mm .
Description: Glossy, solid shell, broad conical, with width attaining about 60% of height, consisting of 5 convex to near straight-sided whorls.Protoconch is not preserved; early whorls convex to angulated, separated by shallow sutures.Last whorl height attains about 75% of total shell height; grows more strongly in an anterior direction in adult specimens, the point of maximum convexity of the whorls shifting downwards and producing a deeper suture.Base is weakly convex to straight.Aperture is oblique, ovoid, rounded anteriorly, and more or less pointed posteriorly.Peristome slightly thickened, adjoined interiorly by a shallow furrow for the operculum.In lateral view, aperture is inclined to the axis with about 10°.Umbilicus covered or narrowed, slit-like.Shell is covered by opisthocline to slightly opisthocyrt growth lines, which sometimes become stronger and form small riblets.Additionally, shell surface occasionally bears irregular spiral wrinkles.

Remarks:
The syntype series of BRUSINA (1874a) comprises shells from the Pliocene of Kravarsko (church) in central Croatia and from Podvinje (Čaplja) in northeastern Croatia.Additionally, he had a few opercula from Bečic as well, which he assigned to the present species.MILAN et al. (1974) erroneously considered the syntype illustrated by BRUSINA (Coll.NHM Zagreb Inv.No. 3852-1492/1) as the holotype, which according to ICZN Art.74.5 does not classify as a valid lectotype designation.Therefore, following the ICZN formal provisions of Art.74.7, we designate this specimen, illustrated in BRUSINA (1874a, pl. 5, figs. 13-14), as the lectotype.Type locality is the slope beneath the church in Kravarsko; the type stratum belongs to the LVB V. kochanskyae zone.
The differences to B. tentaculata are the larger size and the shape of the whorls with maximum convexity in a more abapical position.PILAR (1873) discovered the present species in the wood between Dubranec and Dragonošci together with Theodoxus sagittiferus [= T. semiplicatus], Viviparus fuchsi [= V. kochanskyae], and Microcolpia friedeli (among others), which could imply the same stratigraphic position as for Kravarsko.NEUMAYR & PAUL (1875) observed N. vu kotinovici in the V. stricturatus zone of Gromačnik in NE Croatia and detected B. tentaculata in LVB (Cernik, Čaplja, Gornji Raić) and MPB (Gromačnik).PENECKE (1884) only distinguished B. tentaculata in the Pliocene of northeastern Croatia, particularly in the Čaplja trench (LVB, UVB), Malino (LVB-UVB) and Sibinj (MVB).Interestingly, BRUSINA (1885) doubted the presence of B. tentaculata in Slavonia, but (in contrast to WENZ, 1928) did not synonymize the respective identifications with B. vukotinovici.This is probably because the latter identifications were never documented by an illustration.A reinvestigation of the material from the Pliocene of northeastern Croatia is necessary to solve the species-level content of the Bithyniidae there.From central Croatia, KOCH (1917) (1883).WENZ (1928) was the first to synonymize the latter identification with B. vukotinovici, but still considered B. rumana as separate species.Note that GI-ROTTI (1972) again synonymized the latter species with B. vukotinovici, which is followed herein.
Distribution: Lake Slavonia deposits of central Croatia (LVB of Kravarsko, LVB? of Dubranec and Prvonožina) and northeastern Croatia (LVB? of Podvinje/Čaplja, MVB of Gromačnik and other questionable localities as listed below); Pelendavian deposits of the Dacian Basin in Romania, Sienisian to Pelendavian equivalents (late Kimmerian) of SW Moldavia and of SW Ukraine.
Except for Romania, the presence of B. vukotinovici in the Lake Dacia deposits was also listed from the "Levantin" of Giurgiuleşti in SW Moldavia by MACAROVICI (1940).Beyond that, GOZHIK & DATZENKO (2007) documented it from the adjacent SW Ukraine ranging there from the late Pliocene (uppermost Kimmerian) to the early Pleistocene.In the Pleistocene, the species concurs with B. tentaculata.Its presence in the Kuyalnikian of Odessa was documented by BOGACHEV (1961).Its record from the Pleistocene of the Taman Peninsula in SW Russia by VASSOEVICH (1928) was not accompanied by an illustration and cannot be approved.

Remark:
The present species closely resembles species from the Pliocene of Italy, which were treated as Prososthe nia by SCHLICKUM (1972) and ESU & GIROTTI (1975).Most probably, these species do not represent Prososthenia, considering the morphological differences from its type species, which is smaller, bulkier and strongly sculptured.A revision of this group, however, is beyond the scope of the present study.
Description: Glossy, slender drop-shaped shell, comprising up to 7 low convex whorls, and width attaining about 35% of shell height.Shell outline is variable in width, including wider and slender morphologies.Apex is slightly inflated, blunt, with highly convex initial two whorls.The following three whorls are weakly convex and form a regular conical outline; they are separated by distinct, moderately deep to shallow sutures.Shell height increases faster than the diameter, producing the typically drop-shaped appearance.In later ontogeny whorl flanks are sub-parallel to the axis, weakly convex, often centrally flattened, with slightly deeper sutures than before.The last whorl forms about 55% of the total shell height, is globose with a slightly convex shell base.Umbilicus is covered or very narrow.Aperture is ovate to drop-shaped, oblique.Posterior shell portion of the aperture is thickened and attached to the base of the preceding whorl.Shell is covered with orthocline growth lines.A weak subsutural band is present in a few specimens.
Remarks: BRUSINA (1874a, b) based this species on specimens from the localities of Bečic, Podvinje (Čaplja) and Sibinj in Slavonia (NE Croatia).We designate herewith the specimen from Čaplja illustrated by BRUSINA (1874a, pl. 4, figs. 13-14) and stored at the NHM Zagreb (Inv.No. 3051-697) as the lectotype.Its previous reference as "holotype" in MILAN et al. (1974) does not constitute a valid lectotype designation (ICZN Art.74.5).slavonica.While WENZ (1926) synonymized it with P. sla vonica, STEVANOVIĆ (1951) treated it as an independent subspecies, which he also reported from Sremski Karlovci.Because of the morphological and stratigraphical differences, we consider both taxa as separate species.P. praeslavonica is perhaps the phylogenetic ancestor of P. slavonica.The systematic position of both species within Prososthenia is still questionable, given the highly elongate shell and the thin peristome (cf.BRUSINA, 1897).Unfortunately, we lack material for P. praeslavonica and do not know about the more diagnostic features such as protoconch sculpture of either specices, which is why a systematic revision would be based on weak ground and is therefore avoided here.
Descriptions: Small, solid, bulky shell with up to 4 whorls, and width attaining about 80% of shell height.Apex is blunt.Spire trochiform, stepped, with deep sutures, flattened, subhorizontal ramps and slightly convex flanks.Blunt angulation present between ramps and flanks.Last whorl large, attaining 83% of shell height, showing straightened, oblique shell base.Aperture is ovate-semicircular, inclined by 45° toward axis.Peristome thickened, slightly protruding anteriorly and posteriorly, forming a continuum with the callus pad.Umbilicus covered by the latter.Apertural plane pos teriorly inclined.Dense opisthocline growth lines present on glossy exterior shell.
Remarks: NEUMAYR (1869) identified his specimen from the LVB of Cernik (Sv.Linart church; STUR, 1862; NEUMAYR & PAUL, 1875) erroneously with the Recent Lithoglyphus naticoides (PFEIFFER, 1828), which has a distinctly lower spire and a bulkier last whorl.The specimen he illustrated on pl.13, fig. 10 (height x width = 8.0 x 5.3 mm) is stored in the collection of the GBA (Inv.No. 1869/001/ 0068).BRUSINA's (1874a) specimens derive from a number of localities from the central part of Lake Slavonia as well as from Vlaško Kostanjevlje (= Kostanjevec) in Kravarsko and Farkašić donated to him by Lj. v. FARKAŠ-VU KO TI-NOVIĆ.He claimed these are somewhat smaller in size than those from NE Croatia and identified them as Recent L. fus cus PFEIFFER, 1828, which was followed by NEUMAYR & PAUL (1875).
The introduction of L. decipiens BRUSINA, 1885 was a text-note referring to all specimens from Slavonia previ-ously misidentified with L. fuscus.Later, BRUSINA (1897) provided synonymy to his new species and illustrated specimens from Kovačevac and Malino.The specimen from  was erroneously referred to as the "holotype" by MILAN et al. (1974).According to PENECKE (1884), the sediments at Kovačevac belong to the UVB V. zelebori zone.
From the LVB of Malino, NEUMAYR in NEUMAYR & PAUL (1875) described the new species L. histrio which he presumed to be an aberrant variation from L. fuscus sensu BRUSINA.It differs from the present species in its elongated, ovoid morphology.
L. kinkelini BRUSINA, 1894 from the Portaferrian of Kurd (SE Hungary) -illustrated for the first time in BRU-SINA (1902) -was synonymized by WENZ (1928) with L. decipiens.WENZ (1928) also listed Bithynia brusinai HA-LAVÁTS, 1903 from the latest Pannonian of Kötcse SE Balaton (Hungary) as well as L. naticoides sensu HALAVÁTS (1888) from the V. boeckhi zone (Pleistocene) of Szentes in SE Hungary as synonyms of the present species.However, KROLOPP (1976b) approved HALAVÁTS' original identification, pointing out that L. decipiens is absent in the Pleistocene of SE Hungary.The presence of L. decipiens at Kötcse was confirmed by MÜLLER & MAGYAR (1992).STEFANESCU (1896) erroneously introduced Litho glyphus neumayri as a new name for the specimens from Slavonia and Romania identified previously with L. fuscus, apparently unware of L. decipiens.He referred the authorship to BRUSINA, mentioning the corresponding collection label seen at the NHM Zagreb.Moreover, he was apparently unaware of introducing a primary homonym of Lithoglyphus neumayri SINZOV, 1877.Anyway, L. neumayri is an objective junior synonym of L. decipiens.

Distribution:
The species occurs in numerous localities of Lake Slavonia, ranging from the LVB to the UVB (PE-NECKE, 1884) and Lake Dacia (see below).The oldest records are listed from the Portaferrian (late Pontian sensu STE VANOVIĆ et al., 1990) of Hungary (e.g., Kötcse) and the late Maeotian of SW Ukraine (ROSHKA, 1973).Particularly the Ukrainian record extends the stratigraphic and geographic range of the species enormously, which is why a careful revision of ROSHKA's material is required.
In addition to numerous central Lake Slavonian occurrences (LVB to UVB), NEUMAYR & PAUL (1875) referred two specimens from the upper Portaferrian Lake Pannon deposits at Grgeteg and Sremski Karlovci (both NW Serbia) to this species.
WENZ (1942)  Records by WENZ (1928) that could not be confirmed are from (1) the Dacian of Araci (=Arpatac) in the Braşov basin, not confirmed by JEKELIUS (1932), (2) the Upper?Miocene from Sarajevo (Lukavica) based on "Lithoglyphus cf.fuscus" in NEUMAYR (1880b), an identification automatically related to L. decipiens by WENZ (1928), although it has never been recorded from the Dinarides (e.g., HAR Z-HAUSER & MANDIC, 2008), and (3) the Pliocene of the area around Orahovac (Kosovo) based on "Lithoglyphus fus cus" in PAVLOVIĆ (1903).All these occurrences are high ly dubious and have never been described or illustrated.MACAROVICI (1940) illustrated specimens from the Dacian of Dmytrivka in SW Ukraine belonging palaeogeographically to the easternmost part of Lake Dacia.In addition, he recorded this species from numerous other Dacian localities in Moldova as well as in the SW Ukraine.Dimensions: Height x length (fragment of the anterior shell) -30.7 x 28.4 mm 32 x 50 mm reconstructed).

Class
Descriptions: Shell thick, moderate in size and convexity, elongated with height (reconstructed) attaining about 65% of length.Outline is inequilateral with inflated, prosogyrate umbo shifted anteriorly and projecting over the hinge line.Anterior and ventral margins are rounded; posterior margin is not preserved, possibly sub-rectangular.Transverse keel is present posterioventrally.Shell wall is nacreous, lamellate, maximum of 4 mm thick.Exterior surface bears coarse, irregularly undulated to zigzag-patterned concentric lirae in the first 8 mm of ontogeny.Afterwards, the shell exterior is smooth, apart from projecting growth constrictions and very fine growth lines.Hinge comprises one massive, trigonal pseudocardinal on the right valve, subdivided by vertical grooves, adjoined by two elongated, pseudocardinals on the left valve.Anterior adductor scar is deep and rugose.

Remarks:
The holotype by monotypy is one fragmented left valve from Kravarsko (Burdelj wood) with a missing posterior shell portion and centrally fragmented hinge (NHM Material: VGK-39 (3 specimens from sample no.13, and 1 specimen from sample P1).
Descriptions: Shell ovoid, fragile, inequilateral, posterioventrally elongated with length attaining 85% of height, with umbo shifted posteriorly, and the anterior part strongly protruded.Moderately convex, with convexity attaining 32% of total height, and with dorsally shifted point of maximum convexity.Opisthogyrate umbo is slightly projecting over the hinge line.Anterior margin strongly convex, other margins are weakly convex.Exterior shell surface bears regular, projecting sharp-topped commarginal lirae interrupted by concave growth constrictions (two in specimen on Figures 9.5-6).Adductor scars are of similar medium size but of different shapes.The posterior one is subcircular, anterior one narrowly ovate inclined toward the umbo.Pallial line is integripalliate.Right hinge has elongated lateral teeth, two massive anteriorly and two slender posteriorly.Cardinal teeth are much smaller but distinct, elongated, inclined, joined beneath the umbo, the posterior one longer than the anterior.
Remarks: Holotype by monotypy is a single left valve (height x length = 12.9 x 10.2 mm) from the V. vukotinovici zone of Novska illustrated by NEUMAYR & PAUL (1875) on pl. 8, fig.35 and stored in the GBA (Inv.No. 1875/002/ 0028).BRUSINA (1897) illustrated for the first time a right valve and additionally a hinge detail of the left valve of the species from the type locality.
The record of P. solitarium by CAPELLINI (1880) from the late Miocene of Italy is a misidentification and does not even match at the genus level, showing a completely different hinge type.Note that Pisidium solitarium sensu PRIME (1870) is a nomen nudum introduced in a synonymy list of "Pisidium henslowianum, Jenyns" (=Pisidium henslowanum (SHEPPARD, 1825)) and therefore no senior homonym.

ACKNOWLEDGMENT
Our thanks go to D. PAVELIĆ and V. ANISTRATENKO for the thorough reviews of the manuscript.This study contributes to the project "Freshwater systems in the Neogene and Quaternary of Europe: Gastropod biodiversity, provinciality, and faunal gradients" financed by the Austrian Science Fund (FWF project no.P25365-B25) and to the project "Basic Geological Map of Republic of Croatia 1:50 000" financed by the Ministry of Science, Education and Sports of the Republic of Croatia (project no.181-1811096-1093).

Figure 2 :
Figure 2: Chronostratigraphic cor re lation table for the late Neogene indicating the stratigraphic posi tions of the units referred to in the present study.Standard chronostra tigraphy derives from HILGEN et al. (2012).Compilation of Paratethys re gional stages is adapted from NEU BAUER et al. (2015b).Palaeoge ographic connection events are mark ed by arrows.The Cernikian is a new Pannonian Basin stage defin ed in the present study.
VGK-39 is located within Kravarsko, 330 m NW of the Holy Cross church, at 215 m a.s.l. on the same slope as the previous locality, 80 m W of the road junction (45.588015°N 16.044973°E).This locality has no exposed section.The sample was taken from a shell accumulation entirely disturbed by the land-slide very similar to Kra-I.VGK-38 is located 3 km NE of Donji Hruševac, 7.3 km SE of the previous sample point, in the Veliki Burdelj wood, 230 m NW of the path to Brenčići, in the trench of the NE flowing ephemeral stream at 152 m a.s.l.(45.551984°N 16.084993°E).The collected gastropod shell originated from debris accumulated by the stream.The shells derive from an unknown position within the Cernikian deposits exposed along the trench in upstream direction.The distance to the stream head of only 260 m makes longer transport improbable.

Figure 4 :
Figure 4: The studied sections.Arrow marks the mollusc sample.

Figure 5 :
Figure5: Stratigraphic correlation of the Lake Slavo nia stratigraphic units with the Dacian Basin chrono stratigraphy afterVAN BAAK et al. (2015).Calibration of Viviparus biozones is based mainly on LUBENESCU & LUBENESCU (2008) and own data (see text).Stand ard chronostratigraphy followsHILGEN et al. (2012).Note the indicated position of the two stratigraphic levels identified in the studied sites and the one mil lion year gap between them.This agrees with previ ously published results showing the absence of mid dle Viviparus beds in western Lake Slavonia.This implies a 1 myr long retreat of the Lake Slavonia east wards with subsequent shortterm flooding during the Pliocene Climate Optimum.

Figure 6 :
Figure 6: Palaeogeographic map of the Pliocene after NEUBAUERet al. (2015a)  indicating lakes from where the species observed at the Vukomeričke Gorice hills were previously reported.Note that most of these occurrences are proven to be erroneous after the present revision (see Table3).
documented specimens from the Pyrgula eugeniae beds (late Dacian; ANDREESCU et al., 2013) of the area around Iordăcheanu/Plavia/Valea Urloii and the late Romanian of Valea Seacă.He listed this species in the Dacian Basin from the middle Pontian to the late Romanian.PAPAIANOPOL & MARINESCU (1995) illustrated specimens from the Getian of Moreni in the Dacian Basin and Parscovian of Tudor Vladimirescu well at the Moesian platform (both Romania).PAPAIANOPOL et al. (1995) cited it from two additional -Getian and Parscovian -localities.Fi-nally, PANĂ (2003) illustrated specimens from the Pelendavian (middle Romanian) of Plopşoru (Olari) in the Dacian Basin.Additional localities in Romania, where this species was cited from but not more recently documented from, go back to WENZ (1928; Dacian and Romanian), KREJCI-GRAF & WENZ (1932; upper Pontian, Dacian, upper Romanian), and PAPAIANOPOL et al. (2003; late Dacian and Parscovian).

Table 2 :
Stratigraphic distribution of the identified taxa in the revised Lake Slavonia chrono and biostratigraphic scheme.Integrating results by NEU MAYR & PAUL