The quantitative small mammal data (specimen numbers per species; Online Appendix) are based on the collections in the NHMW and the data presented in the Catalogus Fossilum Austriae of Daxner-Höck and Höck (2015) and in Ziegler (2006). For counting we took all available specimens, i.e. skulls, partial skulls, isolated premolars, molars and jaws with or without teeth. Not included in specimen numbers are incisors and postcranials, except the humerus of Talpidae. The representation of small mammals within the various Pannonian localities of the Vienna Basin is rather inhomogeneous. The stratigraphically older assemblages are especially strongly taphonomically biased toward large mammals. Thus, Lower Pannonian localities with very few species and low specimen numbers are contrasted by extremely rich assemblages of the Upper Pannonian with thousands of specimens. A statistical comparison of these assemblages based on specimen numbers is of little significance. Therefore, we used only presence/absence data for statistical analysis, to calculate a small mammal diversity curve with the software PAST (Hammer et al., 2001) including originations and extinctions (Fig. 2). In addition, a two-way cluster analysis was performed on a reduced data set, from which singletons and persisting species were removed (Fig. 3) to illustrate similarities between the assemblages and to define species-groups, that are characteristic for certain intervals.

The deposition of limnic and fluvial sediments, and the respective mammal localities, closely related to the history of the northern Alpine Foreland Basin (NAFB), the Vienna Basin and the Pannonian Basin, and to the origin and development of Lake Pannon. At the Middle/Late Miocene transition (= Sarmatian/Pannonian boundary), i.e., at about 11.6 Ma, a glacioeustatic sea-level drop caused the final disintegration of the Paratethys Sea (Harzhauser et al., 2004). The Paratethys split geographically into the eastern Paratethys and, west of the Pannonian basin system, Lake Pannon arose. Lake Pannon attained a maximum length of 860 km (from the Karlovac Basin in the west to the Transylvanian Basin in the east) and a width of 550 km (from the Vienna Basin in the north to Belgrade in the south), covering an area of about 290,000 km² (Harzhauser and Mandic, 2008, Harzhauser et al., 2004 and Magyar et al., 1999). In Austria, Lake Pannon covered the northern and southern Vienna Basin and the Austrian part of the Pannonian Basin.

During the Early Pannonian, the fluvial system Palaeo-Danube and its delta arose, which entered Lake Pannon in the northwestern part of the Vienna Basin. In the delta area, huge wetland environments established, as evidenced by mollusc- and vertebrate-bearing fossil sites such as Atzelsdorf, Bullendorf, Gaweinstal, Mariathal and Magersdorf. During the Middle Pannonian, a last level rise of Lake Pannon mostly destroyed these wetlands.

In the Late Pannonian, Lake Pannon disappeared from the Vienna Basin step by step, and established its northwestern coast in the Hungarian Basin (Magyar et al., 1999). Consequently, the drainage systems from the Alps and the NAFB entered the central Vienna Basin and formed extended floodplains with oxbows, rivulets and floodplain-lakes as reconstructed for the localities Götzendorf, Stixneusiedl and Neusiedl am See (Harzhauser and Tempfer, 2004), and a fringe of freshwater lakes became established along the western margin of the central Vienna Basin as reconstructed for the localities Richardhof-Golfplatz, Richardhof-Wald and Eichkogel (Daxner-Höck and Höck, 2009 and Harzhauser and Tempfer, 2004).

In the western part of Austria, the drainage system of the Alps transported gravels and sands northwards into the NAFB of Upper Austria. The highest and youngest member of this sequence is the “Hausruck Gravel”. Its interbedded sandy-silty layers yielded the Upper Miocene vertebrate fauna Schernham (Daxner-Höck, 2004b).

The Upper Miocene small mammal record of the Vienna Basin and adjacent basins is one of the best in Central Europe. Stratigraphically, the studied sections provide mammal faunas or groups of mammal faunas from eight time intervals of the Pannonian Stage (Fig. 1 and Fig. 2):

1. Atz: The Lower Pannonian localities Atzelsdorf (Atz: E 16°32′39″ N 48°30′37″), Gaweinstal, Bullendorf, Mariathal and Magersdorf are part of the “Hollabrunn-Mistelbach” Formation in Lower Austria. All these localities can be correlated with the Mytilopsis hoernesi Zone (= Pannonian Zone C) and roughly range around 11.2 to 11.0 Ma (Harzhauser et al., 2004). Moreover, in these localities the lower boundary of the Vallesian and Mammal Zone MN9 is indicated by the first occurrence of Hipparion s.l. This unit represents sediments of the Paleo-Danube and its delta. The depositional environments range from fluvial channels and crevasse splays to oxbow lakes. Large mammals (e.g. Hipparion s.l.) are very abundant in these deposits whilst the number of small mammals is rare. To achieve a representative number we united the findings of Atzelsdorf, Bullendorf, Gaweinstal, Magersdorf and Mariathal. Nevertheless, only twenty small mammal species represented by 92 specimens are recorded from this interval. For detailed data on stratigraphy, sedimentology, taphonomy and taxonomy of these localities see Daxner-Höck, 1996 and Daxner-Höck, 2004a, Daxner-Höck and Bernor (2009), Harzhauser (2009), Harzhauser et al., 2004, Harzhauser et al., 2011 and Harzhauser et al., 2003, Nehyba and Roetzel (2004), Steininger (1999).

2. Vö: The Middle Pannonian localities Vösendorf (Vö), Inzersdorf and Hennersdorf (E 16°19-21′ N 48°06-07′) are situated at the western margin of the central Vienna Basin in Lower Austria. These localities can be correlated with the Lymnocardium schedelianum Zone (= Pannonian E) and range around 10.4 to 10.5 Ma (Kern et al., 2012). They represent pelitic offshore clays of Lake Pannon. Rare levels with terrestrial mammals were formed by transport from the shores during high energy events of Lake Pannon. Again, large mammals are predominant whilst small mammals are very rare in the samples of Vösendorf, Inzersdorf and Hennersdorf. Only seven species were detected, represented by only 178 specimens. They indicate the first part of the Lower Vallesian (MN 9a). For data on sedimentology, taphonomy and taxonomy of these localities see Daxner (1967), Harzhauser and Mandic (2004), Harzhauser et al., 2004 and Harzhauser et al., 2003, Kern et al., 2012 and Kern et al., 2013, Papp (1951) and Papp and Thenius (1954).

3. RH: The Upper Pannonian fauna of Richardhof-Golfplatz (RH: E 16°16′13″ N 48°03′27″) is situated in the central Vienna Basin in Lower Austria. In the course of the Upper Pannonian Lake Pannon disappeared from the Vienna Basin and freshwater deposits established. The vertebrate- and gastropod fauna of a 7-m thick sediment sequence from Richardhof-Golfplatz reveals a swampy freshwater lake environment. The gastropod Prososthenia sepulcralis is indicative for Pannonian Zone F (around 10.1 Ma). The small mammal assemblage comes from intercalated silty clay layers and comprises 42 species represented by 1274 specimens. They indicate the second part of the Lower Vallesian (MN9b). Data on sedimentology, stratigraphy and taxonomy are presented in Daxner-Höck and Höck, 2009 and Daxner-Höck and Höck, 2015, Harzhauser and Binder (2004), Harzhauser and Tempfer (2004), Harzhauser et al. (2004) and Ziegler (2006).

4. Gö/Stix: The Upper Pannonian localities Götzendorf (Gö: E 16°34′59″ N 48°00′27″) and Stixneusiedl (Stix: E 16°40′13″ N 48°03′12″) are situated in the southern Vienna Basin in Lower Austria. The depositional environment was characterized by floodplains and wetlands. The mollusc fauna indicates a correlation with the Mytilopsis neumayri Zone (= Zone F of Papp, 1951). The mammal fauna correlates with the Lower Vallesian (MN9b). The two coeval small mammal faunas yielded 34 species represented by 1163 specimens. The localities range around 9.7 to 9.9 Ma. More data are provided by Bernor et al. (1993), Daxner-Höck (2004a), Daxner-Höck and Höck, 2009 and Daxner-Höck and Höck, 2015, Harzhauser and Tempfer (2004), Harzhauser et al. (2004), Rögl et al. (1993).

5. Rh/NS: The Upper Pannonian locality Richardhof-Wald (Rh: E 16°16′15″ N 48°03′35″) is situated at the western margin of the central Vienna Basin in Lower Austria, and Neusiedl am See (NS) at the eastern margin of the southern Vienna Basin in Burgenland. The small mammals of these two faunas indicate a correlation with the first part of the Upper Vallesian (MN10a). The lacustrine (Rh) and fluvial deposits (NS) are correlated with the uppermost Pannonian Zone F. The first occurrence of the murid Progonomys hispanicus indicates mammal zone MN10 (Agusti et al., 1997, Garces et al., 1996 and Van Dam, 1997). Consequently, the age is around 9.7 Ma. Both fossil layers yielded together 1632 specimens representing 39 species. Details on the sections are presented by Daxner-Höck, 1996 and Daxner-Höck, 2004a, Daxner-Höck and Höck, 2009 and Daxner-Höck and Höck, 2015, Rögl et al. (1993) and Ziegler (2006).

6. Sch: The locality Schernham (Sch: E 13°36′38″ N 48°10′40″) is situated in the NAFB in Upper Austria. The estimated age ranges around 8.9 to 9.1 Ma. From the sand and gravel pit Schernham 45 small mammal species are represented by 2307 specimens. The mammals indicate a correlation with the second part of the Upper Vallesian (MN10b). Information on taxonomy and stratigraphy is given in Daxner-Höck, 2004a and Daxner-Höck, 2004b, Daxner-Höck and Höck, 2009 and Daxner-Höck and Höck, 2015 and Ziegler (2006).

7. Ko: The Upper Pannonian deposit Kohfidisch (Ko: E 16°20′39″ N 47°08′52″) is situated in the Pannonian Basin in Burgenland near Kirchfidisch and represents a karstic cave and fissure system in Devonian limestones. The mollusc assemblages point to a correlation with the Pannonian zone G of the Vienna Basin. The mammal assemblage corresponds to the Lower Turolian (MN11). The estimated age is around 8.5 to 8.6 Ma. Numerous excavation campaigns resulted in a huge collection of 21,754 specimens; nevertheless, the number of species (41) is lower than in Schernham and Richardhof-Golfplatz. Details on regional geology and taxonomy are presented by Bachmayer and Zapfe (1969), Bachmayer and Wilson (1970), Daxner-Höck (2004a) and Daxner-Höck and Höck (2009).

8. Eich: The youngest assemblage was collected at Eichkogel (Eich: E 16°17′32″ N 48°03′55″) at the western margin of the Vienna Basin in Lower Austria. The mollusc and small mammal fauna was excavated from silty clay about 10–12 m below the freshwater limestone forming the top of the Eichkogel hill. The extraordinarily rich mollusc fauna of the lacustrine clay and limestone is the type fauna for the Upper Pannonian Zone H. The mammal assemblage represents the Lower Turolian (MN11). Its estimated age is 8.3 Ma. From the Eichkogel clay 2029 specimens of 35 species were collected. Details on stratigraphy, taxonomy and further references are given in Daxner-Höck (2004a), Daxner-Höck and Höck, 2009 and Daxner-Höck and Höck, 2015, Harzhauser and Binder (2004), Harzhauser et al. (2004) and Ziegler (2006).

From these localities the fossil record is partly rare and partly very rich. Totally, almost hundred small mammal species were identified, i.e. 51 Rodentia, 36 Eulipotyphla (“Insectivora”), seven Chiroptera and five Lagomorpha (details in Online Appendix). Some species or groups of taxa are characteristic for certain stratigraphic levels and allow correlation with the European land Mammal Zones MN9 to MN11 of the Vallesian and Lower Turolian (Steininger, 1999).

The suprageneric composition of small mammal communities within the various localities of the study area is rather homogeneous except for the Atzelsdorf and Vösendorf complexes. These assemblages of the Lower and Middle Pannonian (MN9a) show incomparably low species and specimen numbers (Table 1, Table 2 and Table 3), and therefore will be excluded from further analyses.

All considered assemblages of the Upper Pannonian (MN9b to MN11b) show highest species numbers of Rodentia (20–24 taxa) followed by Eulipotyphla (12–21 taxa). Chiroptera and Lagomorpha are present in low numbers or are absent. Only in Schernham numbers of Eulipotyphla (21 taxa) and Rodentia (20 taxa) are almost equal (Table 1).

The analysis of the Rodentia (Table 2) documents high diversities of Gliridae, Sciuridae (tree-squirrels), Cricetidae (Paracricetodontinae, Cricetodontinae and Cricetinae) in all assemblages of the Upper Pannonian. Many of these taxa can be traced back to the Middle Miocene or to Middle Miocene ancestor groups. Gliridae and Cricetidae reach the highest species numbers in the two Richardhof localities (RH/MN9b and Rh/MN10a), Sciuridae in Schernham (MN10b), followed by Götzendorf (MN9b). The species numbers of Eomyidae and Castoridae are comparatively low. The immigrants Microtocricetus and Eozapus reached the Vienna Basin in MN9, Murinae in MN10, Hystrix, Epimeriones and Ischymomys in MN11. These immigrants retain low species numbers, but – except Ischymomys – developed high individual numbers.

Eulipotyphla (Table 3) are represented by Erinaceidae, Plesiosoricidae, Talpidae, Dimylidae and Soricidae families, with the Talpidae being most diverse followed by the Soricidae. Most striking is the high number of Talpidae from Schernham followed by Richardhof-Wald and Eichkogel. The diversity of Soricidae is rather uniform in all assemblages. Low species numbers of Erinaceidae and Dimylidae are known from all assemblages, and occurrences of Plesiosoricidae are restricted to Götzendorf and Schernham.

Our study confirms that the majority of mammals of the Late Pannonian inhabited forested wetland environments. This observation is evidenced by the high variability of climbing and gliding Sciuridae, Eomyidae and Gliridae species, by the frequency of Castoridae, Dimylidae and Talpidae – most of them are known to live close to waterbodies, in floodplains and wet forests. Although the diversity of small mammal species slowly decreased from the Late Vallesian towards the Early Turolian (Fig. 2), many forest dwellers (Pliopetaurista, Pliopetes, Neopetes, Blackia, Miopetaurista, Glirulus, Keramidomys and Eomyops) persisted to the Turolian in low individual numbers per fauna. Simultaneously, ground dwelling Rodentia (Spermophilinus aff. bredai, Kowalskia fahlbuschi, Kowalskia skofleki, Prospalax petteri, Muscardinus pliocaenicus austriacus, Vasseuromys pannonicus, Myomimus dehmi, Progonomys woelferi, Apodemus lugdunensis and Hystrix) originated and developed significantly higher specimen numbers per fauna than the specialists adapted to humid forested environments (Daxner-Höck, 2004a, Daxner-Höck and Höck, 2009 and Daxner-Höck and Höck, 2015).

Our data suggest a major diversification of small mammal communities after the retreat of Lake Pannon from the Austrian part of the Vienna Basin beginning with the Late Pannonian. This pattern is partly explained by the establishment of forested wetland environments in the entire Vienna Basin, resulting in an increase of available habitats and thus is a regional signal. Nevertheless, the apparent increase in diversity (RH; MN9b) may partly be overemphasised due to the comparatively poor record from the Early and Middle Pannonian (MN9a), when Lake Pannon attained its maximal size and covered large parts of the Vienna Basin. Generally, the associations of mainly forest dwelling small mammals underwent minor diversity changes throughout the Vallesian. Apart from numerous extinctions at the beginning of the Late Vallesian (Fig. 3; clusters I–II; MN10a) no clear indication of a Vallesian Crisis (in the sense of Agusti and Moyà-Solà, 1990) can be deduced from our data (compare also Casanovas-Vilar et al., 2014).

A slight shift in communities is observed with the onset of the Turolian, when the small mammal diversities slowly decreased, and some xerophylic species originated and predominated the mammal spectra by very high individual numbers. This seems to reflect the beginning changing of closed forest environments toward patches of open landscape, as a result of less humid conditions at the Vallesian–Turolian transition.