Stable isotope ecology of Hippotherium from the Late Miocene Pannonian Basin system

Palaeogeography, Palaeoclimatology, Palaeoecology 459 (2016) 44–52

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Stable isotope ecology of Hippotherium from the Late Miocene Pannonian Basin system Michael R. Johnson ⁎, Dana H. Geary Department of Geoscience, University of Wisconsin-Madison, 1215 W Dayton St, Madison, WI 53706, United States

a r t i c l e

i n f o

Article history: Received 14 December 2015 Received in revised form 23 June 2016 Accepted 29 June 2016 Available online 1 July 2016 Keywords: Miocene Stable isotope Hippotherium Hungary Austria Habitat

a b s t r a c t The retreat of the Paratethys Sea in the Middle to Late Miocene left behind a series of intermontane lakes across Central Europe. Ancient Lake Pannon, which existed in present-day Hungary and surrounding countries, was gradually filled in by fluvial sedimentation from 10 to 4 Ma. This infilling allowed for the migration of mammals such as the horse Hippotherium into the Pannonian Basin System (PBS). Stable carbon and oxygen isotope records from Hippotherium are used here to reconstruct changing environmental conditions of the Late Miocene in this region. Our emphasis is on understanding the vegetation and surface water of the basin because these in turn affected the isotopic composition of Lake Pannon. We analyzed the enamel of 68 Hippotherium teeth from 23 localities in the PBS for carbon and oxygen isotope composition. Carbon isotope records indicate that Hippotherium in the central regions of the basin were feeding in more open habitats than those in the northwest. We find no evidence of the expansion of C4 grasses into the PBS. Oxygen and carbon isotope values from the Vienna Basin (NW part of the PBS) generally covary, whereas those from more central regions do not. The oxygen values of the central PBS are generally lower than those of the Vienna Basin. These data suggest that the interior of the PBS was generally dry, which forced Hippotherium to use water sources that were not strongly evaporated, such as rivers originating from outside the basin. The dry interior was likely caused by a rain shadow east of the Alps and north of the Dinarides. Consequently, much of the surface inflow into Lake Pannon would have been influenced by runoff from high elevations around or outside the basin. By understanding the terrestrial environment, better constraints can be placed on lake conditions in future work. © 2016 Elsevier B.V. All rights reserved.

1. Background 1.1. Introduction The three-toed horse Hippotherium quickly became a common component of European faunas after migrating from North America and Asia in the Late Miocene (Bernor et al., 1996, 1988). Our knowledge of the ecology of Hippotherium is largely based upon faunal associations and/or skeletal and dental characteristics, and faunal associations which suggest varied feeding behavior and exploitation of a variety of habitats. Mesowear data indicate that the diets of different species and populations of Hippotherium incorporated browse (Bernor et al., 1999), mixed-feeding (Bernor et al., 2011, 2003a, 2003b, 1999; Kaiser and Bernor, 2006; Wolf et al., 2012), or a large graze component (Bernor et al., 2011; Kaiser and Bernor, 2006). Similarly, limb morphology has been used to distinguish forest-dwellers from more cursorial forms within the same locality (Bernor et al., 2003a, 1999, 1997; Kaiser and Bernor, 2006). Isotope studies of Hippotherium in Western Europe, ⁎ Corresponding author. E-mail address: [email protected] (M.R. Johnson).

http://dx.doi.org/10.1016/j.palaeo.2016.06.039 0031-0182/© 2016 Elsevier B.V. All rights reserved.

Greece, and Asia (Quade et al., 1994; Tütken et al., 2013; van Dam and Reichart, 2009; Wang and Deng, 2005) support the interpretation of an opportunistic feeding strategy, whereas some climate studies assume predominantly grazing behavior based on the hypsodonty of Hippotherium and other herbivores (Fortelius et al., 2006, 2002). Bernor et al. (2011) suggest that both interpretations may be partly true by arguing that later Hippotherium – particularly in the vicinity of the Pannonian Basin System – sought refuge in dwindling forest habitats, while congenerics in Asia and Africa adapted to open grasslands. The purpose of this study is to investigate the feeding ecology of Hippotherium in the Pannonian Basin System through the use of stable carbon and oxygen isotopes. We expand upon the currently limited terrestrial isotope record (Bernor et al., 2011), and use our results to describe local environmental conditions through the Late Miocene. The Pannonian Basin System (Fig. 1) includes the Vienna Basin in the northwest, and the Pannonian Basin, which itself consists of several subbasins (Rasser et al., 2008). This system contained Lake Pannon, a relic of the Paratethys Sea that covered most of Hungary, and parts of several other neighboring countries. The lake was first isolated 12 Ma by falling sea levels (Magyar et al., 1999). After a 2 myr period of transgression, it was filled in from 10 to 4 Ma by the prograding delta of the

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Fig. 1. Map of the Pannonian Basin System (bold outline) with localities sampled in this study. Numbers correspond to localities listed in Table 1. Stars represent capital cities for reference.

paleo-Danube River (Magyar et al., 2013, 1999; Popov et al., 2006). The distribution of mammals - including Hippotherium- around Lake Pannon tracked the changing margins of the lake (Nargolwalla et al., 2006), moving from the northwest to the southeast. Unfortunately, the nature of environmental and climatic change regionally is still a matter of contention. Terrestrial ecosystems in the vicinity of Lake Pannon included coniferous and deciduous forests, swamp forests, open woodlands, and grasslands (Ivanov et al., 2011, 2002; Kern et al., 2013, 2012; Kováč et al., 2006). Opening ecosystems and Late Miocene aridity have been inferred from the increasing frequency of hypsodonty in mammals (Fortelius et al., 2006, 2002), as well as some paleofloras and pollen (Ivanov et al., 2011, 2002; Kováč et al., 2006), whereas cenograms of mammalian communities (Costeur et al., 2007) and other paleofloras (Bruch et al., 2011, 2007, 2006; Mosbrugger et al., 2005) argue for humid conditions up to, and perhaps even into the Pliocene. Such a humid climate would have been unsuitable for the expansion of grasslands. Furthermore, those humid conditions are argued to have been wetter than the present, whereas the record from fossil reptiles and amphibians indicate conditions drier than the present (Böhme et al., 2011, 2008).

1.2. Stable carbon isotopes The carbon isotope ratio of structural carbonate in mammalian tooth enamel reflects the composition of diet (Cerling and Harris, 1999; Lee-Thorp and van der Merwe, 1987; Lee-Thorp et al., 1989a). In modern ecosystems with highly stratified plant δ13C values, the δ13C of tooth enamel of herbivores can cover a wide range depending on their feeding habits (Cerling et al., 2004; Lee-Thorp and van der Merwe, 1987). The δ13C values of fossil herbivores can be used to identify feeding niche and to distinguish closed versus open systems (Bocherens et al., 1996; Lee-Thorp et al., 1989a, 1989b; MacFadden and Cerling, 1996; Secord et al., 2008). The apparent enrichment in 13 C between diet and tooth enamel δ13C values (εenamel-diet) in modern ungulates is about 14.1‰ (Cerling and Harris, 1999).

The δ13C of enamel is influenced by the relative proportion of C3 and C4 plants in the animal's diet, and by the growing environment. C4 plants are not expected to be a major part of the landscape in Central Europe (Cerling et al., 1997; Quade et al., 1994). The major source of variability in Hippotherium δ13C values is environmental. Plant δ13C values tend to be lower in closed-canopy forests due to reduced light availability and CO2 recycling, and higher under drier, more open conditions (Cerling et al., 2004; Farquhar et al., 1989; Kohn, 2010; Medina and Minchin, 1980; O'Leary, 1988; van der Merwe and Medina, 1989). The relationship between plant δ13C and moisture allows for annual precipitation rates to be estimated from enamel δ13C values (Kohn, 2010). 1.3. Stable oxygen isotopes The oxygen isotope composition of carbonate and phosphate in bone and tooth enamel is dependent on the composition of body water, which is in turn controlled by the balance between oxygen influx and outflux (Bryant and Froelich, 1995; Bryant et al., 1996; Kohn and Cerling, 2002; Kohn, 1996; Luz et al., 1984). An herbivorous mammal takes in oxygen as respired atmospheric O2, as drinking water, and as dietary water in plant tissues. Oxygen is lost as respired CO2, waste water, evaporated sweat, and respired water vapor. The relative contributions of each of these components varies with physiology and behavior. For example, semi-aquatic mammals lose less water to evaporation (Bocherens et al., 1996), whereas drought-tolerant species depend little on drinking water (Luz et al., 1984). Additionally, there are fractionations associated with evaporative loss, respired CO2, and respired water vapor that further alter body water depending on their relative importance (Bryant and Froelich, 1995; Kohn and Cerling, 2002; Luz et al., 1984). Nonetheless, the δ18O value of phosphate (δ18Op) in obligate drinkers is proportional to the δ18O value of drinking water (δ18Ow) (Kohn and Cerling, 2002). Enamel carbonate and phosphate are in isotopic equilibrium; the fractionation factor relating tooth enamel carbonate to tooth enamel phosphate (αc-p) is 1.0086 ± 0.0007 (Bryant et al., 1996). These two relationships allow for the composition of

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M.R. Johnson, D.H. Geary / Palaeogeography, Palaeoclimatology, Palaeoecology 459 (2016) 44–52

drinking water to be estimated from enamel carbonates as combined in Eq. (1):

3. Results 3.1. Assessment of diagenesis

  δ18 Ow ¼ δ18 Oc –31:7 =0:9

ð1Þ

However, it is important to note that δ18Ow may vary widely for animals living in the same region (e.g. Hoppe et al., 2004). Drinking water is not the same as precipitation. Rivers originating at high elevation may have much lower δ18O values than immediate precipitation (Dutton et al., 2005). On the other hand, evaporation of standing water may cause the δ18O of a lake or pond to be higher than that of precipitation. Consequently, we interpret the δ18O of enamel to reflect the dominant water source utilized by Hippotherium (local streams or ponds, or larger rivers draining more distant uplands) rather than the composition of precipitation.

Considerable overlap exists in the isotope values of enamel samples and most of the samples of either dentin or cementum (Fig. 2). However, several dentin and cementum samples have δ13C values at least 2‰ greater than typical samples. This separation is taken as an indication of some diagenetic alteration of the less stable dentin and cementum, whereas the original isotopic composition is preserved in enamel. Modeled diagenesis of tooth enamel shows a tendency toward higher δ13C values in altered samples (Wang and Cerling, 1994). Tütken et al. (2013) also found higher δ13C values in diagenetically altered Hippotherium dentin compared to enamel. The lone enamel sample that plots with these altered samples is likely either itself altered or represents contamination of the sample by dentin or cementum as no other tooth from the same locality exhibited similar values. In either case, that sample is excluded from all subsequent analyses.

2. Materials and methods 2.1. Fossil material

3.2. Carbon and oxygen isotopes

Fossil material for this study was made available by the Naturhistorisches Museum - Wien (Vienna Natural History Museum; NHMW) and the Magyar Földtani és Geofizikai Intézet (Geological and Geophysical Institute of Hungary; MFGI). A total of 68 Hippotherium teeth were sampled from 23 localities in the Vienna and Pannonian Basins (Fig. 1). Based on its vertebrate fauna, each locality has been assigned to a mammal zone (MN9 = 11.5–9.7 Ma; MN10 = 9.7– 8.7 Ma; MN11 = 8.7–7.5 Ma; MN12 = 7.5–6.8 Ma; MN13 = 6.8– 4.9 Ma; MN14 = 4.9–4.2 Ma) (Agustı́ et al., 2001). When possible, the fourth premolar or third molar were used for isotopic analysis because these teeth erupt latest in life, and are least likely to retain a nursing signal (Table 1).

Mean enamel δ13C values of localities range from −13.2‰ to −8.7‰ (Table 2), however temporal and geographic variation are difficult to disentangle. Most localities from MN10 and earlier are in the Vienna Basin, whereas most younger localities (MN11–14) are from the central part of the Pannonian Basin (Fig. 3, Table 2). The mean δ13C of central Pannonian Basin localities (− 10.5‰) is significantly higher (t20 = 3.11, p = 0.006) than the mean δ13C of Vienna Basin localities (−12.0‰). However, a comparison of the most heavily sampled intervals – M9 and M11 – shows no significant difference in δ13C values (t14 = 1.05, p = 0.313). The mean enamel δ13C values of all localities are within the range expected for herbivores on a C3 diet (Passey et al., 2002). Values from Vienna Basin localities tend to be lower than values expected for “average” Miocene C3 plants, whereas values from central localities tend to be higher than expectations for “average” Miocene C3 plants. As with carbon, the temporal and geographic components of variation in oxygen isotope values are not easily disentangled. The mean enamel δ18O values of all localities range from − 8.4‰ to −3.9‰ (a 4.5‰ spread; Table 2); by comparison, modern horses from New Mexico exhibit values from − 5.7‰ to 0.6‰ (VPDB, converted from SMOW) (a 6.3‰ spread; Hoppe et al., 2004). In contrast to δ13C, the mean enamel δ18O values of Vienna Basin (−6.4‰) and Pannonian Basin (−7.4‰) localities are not significantly different (t20 = −2.0398, p N 0.05) (Fig. 4). However, there is a significant decrease in enamel δ18O values from MN9 (−6.2‰) to MN11 (−7.4‰) (t14 = 2.294, p = 0.038). Mean drinking water δ18O values from these intervals are estimated at −7.9‰ and −9.4‰, respectively. This shift in drinking water composition, if driven purely by temperature, would indicate a decrease in mean annual temperature of 2–3 °C (Dansgaard, 1964; Fricke and O'Neil, 1999) Such a temperature change is not unreasonable for this interval as inferred from other proxies (Bruch et al., 2006; Ivanov et al., 2002; Montuire et al., 2006). Data from this study were plotted with isotope data from contemporary Hippotherium in France, Germany and the Iberian Peninsula (Tütken et al., 2013; van Dam and Reichart, 2009) (Fig. 5). Covariation between δ13C and δ18O is strongly observed among Vienna Basin localities, but only weakly observed among Pannonian Basin localities (Fig. 5). Vienna Basin localities plot along a gradient bounded by the low values of French and German localities (Tütken et al., 2013) and the high values of Iberian localities (van Dam and Reichart, 2009). Pannonian Basin localities only overlap this gradient where δ13C values are low; δ18O values from central localities do not increase with δ13C.

2.2. Sampling technique A single bulk enamel sample was collected from each tooth. The outer surface of enamel at the sampling site was first abraded, and then powder was collected by drilling a transect along the height of the tooth, taking care not to damage the occlusal surface. From many teeth an additional sample of dentin and/or cementum was drilled as a check on diagenetic alteration of the original isotope signal. Enamel is least likely to be altered because of its low organic content, and dense mineral phase. Dentin and cementum are more vulnerable to alteration due to their higher organic content and less dense mineral phase. A consistent offset between the isotope compositions of these substrates is an indication of diagenesis.

2.3. Preparation and analysis Powders were prepared following the protocol of Koch et al. (1997). Residual organic material was removed by treating powders with 2– 3 wt% NaOCl. Treatment with a 1 M acetic acid with Ca-acetate buffer solution was performed to remove detrital carbonate. Samples were analyzed at the University of Wyoming Stable Isotope Facility using a GasBench II online with a Thermo Finnigan DeltaPlus XP Continuous Flow Mass Spectrometer with an accuracy of ± 0.2‰ for δ18O and ± 0.15‰ for δ13C. Carbon and oxygen isotope values were obtained from the carbonate phase of tooth enamel. Additionally, the stable isotope compositions of dentin and cementum from 33 teeth were measured as a check on diagenetic alteration.

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Table 1 Hippotherium specimens. Locality numbers correspond to map in Fig. 1. NHMW – Naturhistorisches Museum Wien (Vienna, Austria). MFGI – Magyar Földtani és Geofizikai Intézet (Budapest, Hungary). Ages are given by mammal zone (MN) and approximate absolute age. MN

Ma

Taxon

Inst.

Inv. no.

Tooth

1

Locality Gaiselberg

9

11.2

2

Stratzing bei Krems

9

11

3

Phyra, Niederösterreich

9

11

4

Altmannsdorf, Wien XII

9

10.5

5

Oswaldgasse, Wien XII

9

10.5

6

Wienerberg, Wien X

9

10.3

7

Leopoldsdorf

9

10.3

8

Vösendorf

9

10.3

9 10 11 12

Alcsút Bódé Tataros-Derna Sümeg

10 10 10 11

9.7–9 9.7–8.7 9 8.7

13 14

Fonyód Mannersdorf bei Angern

11 11

8.7–8 8.5

15

Gols, Burgenland

11

8.5

16

Prottes

11

8.5

17 18

Ferihegy II Csákvár, Esterhazy

11 11

8.3–8 8.2

19 20

Kenese Kéthely (Somogy)

11 12

8 7.8–7.3

21

Baltavár

12

7.1

22

Polgárdi, Szar-hegy

13

5.3

23

Gödöllő

14

4.2

Hippotherium sp. Hippotherium sp. Hippotherium sp. Hippotherium sp. Hippotherium sp. Hippotherium sp. Hippotherium sp. Hippotherium sp. Hippotherium sp. Hippotherium sp. Hippotherium sp. H. primigenium H. primigenium H. primigenium H. primigenium H. primigenium H. primigenium H. primigenium H. primigenium H. primigenium H. primigenium H. primigenium H. primigenium H. primigenium H. primigenium H. primigenium H. primigenium H. primigenium H. primigenium H. primigenium H. gracile H. gracile Hippotherium Hippotherium Hippotherium Hippotherium Hippotherium H. gracile H. primigenium H. primigenium H. primigenium H. primigenium H. primigenium H. primigenium H. primigenium H. primigenium H. primigenium H. primigenium H. primigenium H. primigenium Hippotherium H. csakvarense H. csakvarense H. csakvarense H. csakvarense Hippotherium H. gracile H. gracile H. primigenium microdon H. primigenium microdon H. gracile H. primigenium H. primigenium H. primigenium H. crassum gervais H. crassum gervais H. crassum gervais H. crassum gervais

NHMW NHMW NHMW NHMW NHMW NHMW NHMW NHMW NHMW NHMW NHMW NHMW NHMW NHMW NHMW NHMW NHMW NHMW NHMW NHMW NHMW NHMW NHMW NHMW NHMW NHMW NHMW NHMW NHMW NHMW MFGI MFGI MFGI MFGI MFGI MFGI MFGI MFGI NHMW NHMW NHMW NHMW NHMW NHMW NHMW NHMW NHMW NHMW NHMW NHMW MFGI MFGI MFGI MFGI MFGI MFGI MFGI MFGI MFGI MFGI MFGI MFGI MFGI MFGI MFGI MFGI MFGI MFGI

1977/1948/0013 1977/1948/0024 1977/1948/0022 1977/1948/0003 1954/0103/0003 1957/0259/0004 1959/0339/0004 1956/0160/0005 2007/0112/0001 2007/0112/0002 2007/0112/0003 1895/0009/0010 1895/0009/0010 1888/0012/0037a 1895/0009/0010d 2012/0149/0009 2012/0149/0023 2012/0149/0015 2012/0149/0006 1974/1685/0072 1974/1685/0086 1974/1685/0088 1974/1685/0089 2012/0142/0012 2012/0142/0006 2012/0142/0010 2012/0142/0002 1891/0007/0010b 1888/0013/0107b 1888/0013/0107c Ob/23 Ob/2400 V. 14,135 V. 10,258 V. 10,251 V. 10,259 V. 10,268 Ob/2380 2015/0111/0009 2015/0111/0010 2015/0111/0006 2015/0111/0003 2015/0197/0001 2015/0197/0002 2015/0197/0003 2015/0197/0004 1958/0293/0008 1958/0293/0013 1958/0293/0007 1958/0293/0022 V-18,384 Ob/4245 Ob/4267/2 Ob/4267/4 Ob/4248/8 Ob/2266 Ob/2410 Ob/2410 Ob/401 Ob/401 Ob/2808 Ob/2817 Ob/2817 Ob/2808 Ob/5388 Ob/5388 Ob/5388 Ob/5388

l P4 r P4 r P4 r p4 upper l m2 l M2 l m3 r M2 r P4 r p4 r M3 l M3 r m2 l P4 l P4 l P4 l P4 r M2 r m3 r P4 r m3 l p4 l m3 r P4 l m3 l P4 r p4 r P4 r P3 r m2 r M3 r m2 l p2 r m3 l m3 r p2 r M3 l p4 l p4 r m3 l m3 l m2 l p4 r p3 r m2 l P4 l M3 l P4 r M3 l p3 l p2 r M2 r M3 l P2 l P4 l P4 l P4 r m3 r p4 r P4 r p4 r P4 l P4 l p4 l m2 r p3 l p2

4. Discussion The carbon isotope composition of Hippotherium tooth enamel should fall into one of three ranges depending on the dominant type

of vegetation in diet. Hippotherium that subsisted on a C3 diet should have enamel δ13C values less than approximately − 8.5‰ in the Late Miocene (Passey et al., 2002), whereas those on a C4 diet should have values greater than approximately 2 to 3.5‰. A mixed diet of C3 and

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M.R. Johnson, D.H. Geary / Palaeogeography, Palaeoclimatology, Palaeoecology 459 (2016) 44–52

Fig. 2. δ13C and δ18O values of Hippotherium enamel (filled squares) and dentin or cementum (open squares). The arrow indicates the expected direction of diagenetic alteration. The diagenetically altered enamel sample has a δ13C value N − 6‰, and is circled.

C4 plants would be indicated by enamel values between − 8.5‰ and 3.5‰. All but one tooth sampled in this study had enamel δ13C values lower than −8.5‰. The sole exception was from Csákvár, with a δ13C value of −7.6‰. These results indicate that C3 plants were the dominant – and most likely exclusive – dietary component of Hippotherium in the Pannonian Basin through the late Miocene, and that sites with the highest δ13C values were vegetated by water-stressed C3 plants. These results agree with several regional studies on Hippotherium and other taxa that also failed to detect C4 plants in Europe during this interval (Cerling et al., 1997; Tütken et al., 2013; van Dam and Reichart, 2009; Wang and Deng, 2005).

Within the C3 spectrum, Pannonian localities represent a wide variety of environments. The lower δ13C values of the Vienna Basin and select Pannonian Basin sites are comparable to localities of Eppelsheim, Germany and Charmoille, Switzerland, which were interpreted as forested habitats (Tütken et al., 2013). Under closed canopy conditions, recycling of CO2 and low light availability tend to decrease plant δ13C values (Farquhar et al., 1989; Medina and Minchin, 1980; van der Merwe and Medina, 1989), and lead to lower

Table 2 Isotope data for 23 localities in the Pannonian Basin System. All values are reported with respect to the VPDB standard. V = Vienna Basin. P = Pannonian Basin

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

±1 SD δ18O

±1 SD

Locality

MN Ma

Basin n δ13C

Gaiselberg Stratzing bei Krems Phyra, Niederösterreich Altmannsdorf, Wien XII Oswaldgasse Wienerberg, Wien X Leopoldsdorf Vösendorf Alcsút Bódé Tataros-Derna Sümeg Fonyód Mannersdorf bei Angern Gols, Burgenland Prottes Ferihegy II Csákvár, Esterhazy Kenese Kéthely (Somogy) Baltavár Polgárdi , Szar-hegy Gödöllő

9 9 9 9 9 9 9 9 10 10 10 11 11 11

11.2 11 11 10.5 10.5 10.3 10.3 10.3 9.7–9 9.7–8.7 9 8.7 8.7–8 8.5

V V V V V V V V P P P P P V

4 4 3 4 4 4 4 3 1 1 1 4 1 4

−13.2 −12.3 −12.7 −11.7 −11.4 −10.8 −11.6 −10.8 −9.7 −10.1 −11.4 −11.3 −8.8 −12.3

0.7 0.6 0.6 0.7 1.3 0.2 0.3 0.8 – – – 1.0 – 0.7

−7.3 −7.8 −6.3 −5.6 −5.1 −5.0 −8.1 −3.9 −6.8 −6.3 −4.0 −8.1 −8.1 −7.4

0.7 0.71 0.6 0.7 1.3 0.2 0.3 0.8 – – – 1.1 – 0.7

11 11 11 11 11 12 12 13 14

8.5 8.5 8.3–8 8.2 8 7.8–7.3 7.1 5.3 4.2

V V P P P P P P P

4 4 1 4 1 2 2 4 4

−12.9 −12.2 −12.3 −8.7 −10.3 −10.0 −11.3 −9.6 −13.1

1.3 1.0 – 1.1 – 0.9 2.1 0.8 0.4

−6.9 −7.2 −7.0 −7.4 −7.2 −6.5 −7.9 −7.2 −8.4

1.4 1.0 – 1.1 – 1.0 2.1 0.8 0.4

Fig. 3. Mean enamel δ13C values from each locality over time. Circles indicate localities from the Vienna Basin. Triangles indicate localities from the central Pannonian Basin. The diamond represents a locality from the eastern Pannonian Basin. Closed squares are data from van Dam and Reichart (2009), and open squares are data from Tütken et al. (2013) (see Table S1). Solid and dashed lines represent the predicted enamel δ13C values of an herbivore consuming “average” and “water-stressed” Miocene C3 vegetation, respectively. Error bars are ±1 SD. Absolute ages are given as lower- and upper-bounds for each MN unit following Agustı́ et al. (2001). Numbered data points refer to localities in Table 2.

M.R. Johnson, D.H. Geary / Palaeogeography, Palaeoclimatology, Palaeoecology 459 (2016) 44–52

Fig. 4. Mean enamel δ18O values from each locality over time. Circles indicate localities from the Vienna Basin. Triangles indicate localities from the central Pannonian Basin. The diamond represents a locality from the eastern Pannonian Basin. Closed squares are data from van Dam and Reichart (2009), and open squares are data from Tütken et al. (2013) (see Table S1). Error bars are ± 1 SD. Absolute ages are given as lower- and upper-bounds for each MN unit following Agustı́ et al. (2001). Numbered data points refer to localities in Table 2.

enamel δ13C values (Cerling et al., 2004; Secord et al., 2008). In contrast, the higher δ13C values of the central Pannonian Basin are consistent with open environments of greater light availability and water stress. The similarity in δ13C values from MN9 to MN11 does not support the pattern of a warm, humid climate predicted by several authors (Bruch et al., 2007; Harzhauser et al., 2007; Mosbrugger et al., 2005) that would lead to decreasing terrestrial δ13C values. Our carbon isotope data agree with the feeding ecologies inferred from prior studies of several of our localities. The low carbon isotope values at Gaiselberg support the interpretation of early Hippotherium as forest-dwellers (Bernor et al., 1988). Later Hippotherium from Sümeg (Bernor et al., 1999) and Baltavár (Kaiser and Bernor, 2006)

49

have similar dental morphologies to each other that indicate mixedfeeding, and similar carbon isotope values that suggest a mixed or marginal habitat. The expansion of dry, open habitats in the Late Miocene was associated with the appearance of the Pikermian chronofauna in the Old World (Eronen et al., 2009). Higher carbon isotope values from the Pannonian Basin indicate comparable opening and drying of the terrestrial environment during intervals that are consistent with the local dominance of Pikermian fauna. In contrast, lower carbon isotope values from the Vienna Basin are in agreement with more humid conditions that were less favorable to Pikermian taxa (Eronen et al., 2009). Kaiser and Bernor (2006) suggest that the regression of Lake Pannon (Fig. 6; Kázmér, 1990; Magyar et al., 1999) was a key factor in permitting such open habitats, and our carbon isotope data supports that inference. The oxygen isotope composition of drinking water estimated from Hippotherium tooth enamel carbonate (δ18Ow = (δ18Oc − 31.7) / 0.9) is lower than that predicted for lake water, but higher than that of high-elevation rainfall (Fig. 7). This comparison is not surprising since Lake Pannon was most likely evaporatively enriched in 18O compared to local rainfall and runoff (likely the primary sources of drinking water), and the specimens sampled did not originate in the mountains. However, we do not argue that our estimated δ18Ow values are representative of precipitation. Hoppe et al. (2004) warn that enamel δ18O should not be treated as a direct proxy for the δ18O of rainfall because local environmental factors also influence the composition of drinking water. In dry, evaporative environments, δ18Ow may be higher than local precipitation (Dutton et al., 2005; Hoppe et al., 2004). In regions of high relief, δ18Ow at lower elevations may actually be lower than local precipitation (a consequence of the well-established relationship between increasing elevation and decreasing δ18O). Streams originating at high elevations carry isotopically light water to lowlands, where it mixes with isotopically heavier local rainfall (Dutton et al., 2005). If this water is incorporated into tooth enamel, then the δ18O of precipitation will tend to be underestimated. Nonetheless, enamel δ18O is useful for assessing relative environmental conditions within the basin. The highest Hippotherium δ18O values reported here are greater than those from the contemporaneous open-habitat localities of Höwenegg,

Fig. 5. Mean enamel δ13C and δ18O from localities in the Pannonian Basin (circles, triangles, and diamond), France, Germany, and Switzerland (MN9 to MN10; open squares) (Tütken et al., 2013) and the Iberian Peninsula (MN9 to MN14; filled squares) (van Dam and Reichart, 2009). Solid and dashed lines represent the predicted enamel δ13C values of an herbivore consuming “average” and “water-stressed” Miocene C3 vegetation, respectively. Error bars are ±1 SD.

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Fig. 6. The shoreline of Lake Pannon began a steady regression ~9.5 Ma allowing for the migration of Hippotherium into the basin interior. Locality numbers correspond to Table 1. Shorelines based on Magyar et al. (1999).

Germany and Soblay, France (Tütken et al., 2013) and overlap with those from contemporaneous localities on the Iberian Peninsula (van Dam and Reichart, 2009). Precipitation on the Iberian Peninsula was likely sourced from the North Atlantic (Quan et al., 2014; van Dam and Reichart, 2009), leading to higher local δ18O due to proximity to the source. Air masses from the North Atlantic would have become depleted in 18O as they moved across the continent (as seen in the lower δ18O values in Germany, France, and Switzerland (Tütken et al., 2013)). The highest δ18O values from the Pannonian Basin System likely

Fig. 7. Estimated water δ18O values from Hippotherium (circles, triangles, and diamond) in comparison to values estimated from lacustrine bivalves (gray squares) (Geary et al., 1989; Harzhauser et al., 2007; Mátyás et al., 1996), fluvial bivalves (open square) (Harzhauser et al., 2007), and precipitation in the North Alpine Foreland Basin (NAFB) and Central Alps (Campani et al., 2012). Water estimates from Hippotherium were calculated using: δ18Ow = (δ18Oc − 31.7) / 0.9 (Bryant et al., 1996; Kohn and Cerling, 2002). Absolute ages are given as lower- and upper-bounds for each MN unit following Agustı́ et al. (2001). Numbered data points refer to localities in Table 2.

result from evaporative enrichment in 18O localities featuring dry, open habitats. This interpretation is supported by relatively high δ13C values at these localities. Several localities in both the Vienna Basin and central Pannonian Basin had low δ18O values similar to the forested localities of Eppelsheim and Charmoille in Western Europe (Tütken et al., 2013), and to the well-known Rudabánya locality in the northeastern Pannonian Basin (Bernor et al., 2004, 2003a, 2003b; L. Eastham, personal communication). Some of these localities also have comparably low δ13C values, which support the presence of closed-canopy habitats. Environmental conditions that lead to higher δ13C values in plants can also lead to higher δ18O values in surface water. Drier and more open habitats can accelerate rates of photosynthesis through increased light availability while also slowing diffusion of CO2 into leaves by causing stomata to close to prevent water loss. These processes reduce carbon isotope discrimination, resulting in 13C-enriched plant tissues (Farquhar et al., 1989). Higher rates of evaporation also occur in such habitats, leading to greater 18O-enrichment in soil water, surface water, and plant water (Gat, 1996; Koch, 1998). Covariation in the δ13C and δ18O values of tooth enamel might be expected. The mean enamel δ13C values from several localities in the central Pannonian Basin very clearly indicate C3 diets from open to waterstressed environments. However, the mean δ18O values from those localities are among the lowest values in this study, and comparable to values from closed forests in Western Europe (Tütken et al., 2013). This discrepancy could be a consequence of 1) diagenesis, 2) altitude, or 3) the source of drinking water. Diagenesis is unlikely to be responsible as these localities are dispersed both spatially and temporally, and diagenetic δ13C values are much higher than values from these localities. Altitude could be a factor because carbon discrimination by plants may be low (and thus plant δ13C values may be high) at high elevation (e.g. Sparks and Ehleringer, 1997), and δ18O of precipitation is lower at higher elevations (Dansgaard, 1964; Poage and Chamberlain, 2001). However, the localities are from the interior of the Pannonian Basin, and so are unlikely to be experiencing elevation effects in terms of vegetation. We prefer the explanation that the pattern of high δ13C

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and low δ18O is a consequence of Hippotherium drinking runoff from high elevations while consuming vegetation in an otherwise dry basin interior. Precipitation estimates based on mammal distributions (van Dam, 2006) show very low annual rainfall during the same intervals – and indeed at the same locations – as δ13C maxima in the Pannonian Basin. The estimated composition of drinking water from enamel (−9 to − 10‰) is similar to the composition of river water (− 9 to − 11‰) estimated from the shells of the fluvial bivalves Margaritifera and Mytilopsis (Harzhauser et al., 2007) assuming an average temperature of formation of ~ 15 °C (Fig. 7). Furthermore, these δ18Ow values are intermediate between those calculated for precipitation in the North Alpine Foreland Basin and at elevation in the Central Alps (Campani et al., 2012), suggesting that Hippotherium were consuming water that is a mix of high and low elevation precipitation. Such mixing is to be expected in montane settings (Dutton et al., 2005). A dry basin interior would result from a rain shadow east of the Alps, which are thought to be close to present-day elevations by the Late Miocene (Campani et al., 2012; Kocsis et al., 2007; Kuhlemann, 2007). Wind directions in the Late Miocene were also comparable to the present (Quan et al., 2014), predominantly from the west, and carrying moisture originating in the North Atlantic. These conditions would drive increased precipitation in the western periphery of the Pannonian Basin, while creating a dry, evaporative interior. Consequently, vegetation from the interior could experience water-stressed conditions while Hippotherium could satisfy its water needs by traveling to sources such as rivers, ponds, and the shores of Lake Pannon. The last option would be quite likely when Lake Pannon reached its maximum extent during MN9 (Magyar et al., 1999), which put localities from the basin margins such as Rudabánya on the ancient lake shore.

5. Conclusions Our stable carbon and oxygen isotope record for Hippotherium spans the duration of Lake Pannon. This record indicates that Hippotherium occupied a mix of closed and open habitats that existed throughout the Late Miocene, with closed habitats most common in the Vienna Basin in the early Late Miocene and open habitats more common in the basin interior in the later Late Miocene. These results support previous interpretations of Hippotherium as an opportunistic feeder, and offer no evidence to support the presence of C4 vegetation. The central Pannonian Basin was drier than the periphery, where Hippotherium were reliant on water originating at high elevation rather than local precipitation for drinking water. Lake Pannon therefore also existed under evaporative conditions, with lake water δ18O influenced by runoff and potentially extrabasinal river flow more than immediate precipitation. Future geochemical investigations of the Pannonian Basin should be conducted with consideration of such terrestrial controls. Supplementary data to this article can be found online at http://dx. doi.org/10.1016/j.palaeo.2016.06.039.

Acknowledgements The authors are grateful to M. Harzhauser, U. Göhlich, G. DaxnerHöck, K. Palotás, and E. Bodor for access to and assistance with specimens and age constraints. Thanks to the staff at the University of Wyoming Stable Isotope Facility for conducting sample analysis. We thank Thierry Corrège, Raymond Bernor, and one anonymous reviewer for their valuable suggestions in improving this manuscript. Special thanks to Imre Magyar and Attila Virág for their valuable comments and conversations. This research was supported by the Weeks Fund of the Department of Geoscience, University of Wisconsin – Madison.

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