The Middle Miocene freshwater mollusk fauna of Lake Gacko (SE Bosnia and Herzegovina): taxonomic revision and paleoenvironmental analysis

During the Early to Middle Miocene the Dinaride mountain chain harbored a series of intramontane lakes, collectively termed the Dinaride Lake System (DLS; Figs 1A–B; Krstić et al. 2003; Harzhauser & Mandic 2008). These tectonically isolated lakes experienced an outstanding endemic evolution of freshwater mollusks. Harzhauser & Mandic (2008, 2010) described the DLS fauna as entity and counted 110 gastropod and 35 bivalve species. New investigations by Mandic et al. (2009, 2011) and De Leeuw et al. (2010, 2011) suggest that the various basins of the DLS have to be considered as separate units with different geodynamic, stratigraphic, and paleoenvironmental histories. Consequently, new analyses of the various mollusk assemblages revealed major differences between single basin faunas (Neubauer et al. 2011, 2012). Only during short phases hydrological connection between selected basins might have persisted to allow temporary faunal exchange. This combination of enduring isolation driving endemic evolution and short-term invasions lead to complex distribution patterns and extensive diversifications, which are hard to decipher in taxonomic terms. Neumayr (1880) and Brusina (1897) provided the first taxonomic papers on the mollusk fauna of the Gacko Basin. These authors partly provided descriptions and illustrations of few taxa, but never established a concise taxonomic frame of the whole basin fauna. Milojević (1966) distinguished between several mollusk