Scholarly article on topic 'Social stratigraphy in Late Iron Age Switzerland: stable carbon, nitrogen and sulphur isotope analysis of human remains from Münsingen'

Social stratigraphy in Late Iron Age Switzerland: stable carbon, nitrogen and sulphur isotope analysis of human remains from Münsingen Academic research paper on "History and archaeology"

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Academic research paper on topic "Social stratigraphy in Late Iron Age Switzerland: stable carbon, nitrogen and sulphur isotope analysis of human remains from Münsingen"

Archaeol Anthropol Sci

DOI 10.1007/s12520-014-0221-4

ORIGINAL PAPER

Social stratigraphy in Late Iron Age Switzerland: stable carbon, nitrogen and sulphur isotope analysis of human remains from Münsingen

Negahnaz Moghaddam • Felix Müller • Albert Hafner • Sandra Lösch

Received: 29 July 2014 /Accepted: 2 December 2014

# The Author(s) 2014. This article is published with open access at Springerlink.com

Abstract The Iron Age cemetery of Münsingen in Switzerland with 220 abundantly equipped burials marked a milestone for Iron Age research. The horizontal spread throughout the time of its occupancy laid the foundation for the chronology system of the Late Iron Age. Today, skulls of 77 individuals and some postcranial bones are still preserved. The aim of the study was to obtain information about diet, mobility and social stratification of the individuals. Stable isotope ratios of carbon, nitrogen and sulphur were analysed for 63 individuals. For all of them, C3 plants were found to be the staple food. There are significant differences between males and females in 613C and 615N values. This points to a gender restriction in the access to animal protein with males probably having more access to meat and dairy products. Differences in 615N values were also observed for different age classes. 634S values indicate a terrestrial-based diet with no significant intake of marine or freshwater fish. Seven adults with enriched 634S values might have immigrated to Münsingen, four of which were found in the oldest part of the cemetery. Furthermore, possible changes of the vegetation are indicated by the more positive stable carbon ratios in the later phases. The results lead to the suggestion that especially

Electronic supplementary material The online version of this article (doi: 10.1007/s12520-014-0221-4) contains supplementary material, which is available to authorized users.

N. Moghaddam • S. Lösch (*)

Department of Physical Anthropology, Institute of Forensic Medicine, University of Bern, Sulgenauweg 40, 3007 Bern, Switzerland

e-mail: sandra.loesch@irm.unibe.ch F. Müller

Bernisches Historisches Museum, Bern, Switzerland A. Hafner

Department of Prehistory, Institute of Archaeological Sciences, University of Bern, Bern, Switzerland

Published online: 14 December 2014

males buried with weapons might have played a special role in the Iron Age society.

Keywords Iron Age . Stable isotopes . Diet. Sex . Age . Grave goods

Introduction

The area surrounding Bern—north of the Alps and in the middle of the Swiss Plateau—provides the largest amount of skeletal material from the Late Iron Age throughout Switzerland. During the Iron Age, the Aare valley between the cities of Bern and Thun seems to have been part of a fairly developed settlement area that extended out to the west into the present-day Cantons Fribourg and Neuchätel. Clusters in the geographical distribution of findings suggest two centres around the Belpberg including Belp, Münsingen, Rubigen and Niederwichtrach and around the Bern-Enge Peninsula which is encircled by the Aare River. Bern-Enge was probably the most important oppidum in Late Iron Age Switzerland (Müller 1998). Oppida are pre-urban settlements with defensive structures, and further sites of this type are known on the Swiss Plateau (Jud and Ulrich-Bochsler 2014).

The Late Iron Age burial site of Münsingen-Rain is situated in the Aare valley between Bern and Thun (Fig. 1). It was excavated in 1906 and first published by Jakob Wiedmer-Stern (1908). Due to the size of the burial site, the well-documented excavation and the abundance of grave goods Münsingen is an indispensable reference for chronological aspects of the Late Iron Age. As the burials were laid out from north to south, the 220 graves provide important archaeological information on horizontal stratigraphic dating (Müller 1998). The skeletal remains lay mostly supine and extended, without male, female or subadult groupings within the cemetery. In Fig. 2, graves are shown as numbers illustrating

Fig. 1 Geographical location of Münsingen in the Canton of Bern (modified after Hodson 1968)

the horizontal spread from the earlier to the later phase. Further work on the chronology was conducted by the British archaeologist Frank R. Hodson (1968) with emphasis on the types of fibulae. The chronological phases for the Late Iron Age in Switzerland are defined as follows (Müller et al. 1999): La Tene A from 450 to 400bc (LTA), La Tene B from 400 to 260bc (LTB) and La Tene C from 260 to 150bc (LTC). The northern part of the site dates to the LTA period, and the last burials in the south date to the LTC period. The whole time span covers approximately 420 to 240 bc. The extraordinary abundance of grave goods and the continuity of the cemetery led to the assumption that the entire Münsingen population was of high social status. Additionally, the relatively long occupation time (from 420 to 240 bc) of the cemetery is exceptional (Müller et al. 2008).

In the past, the human remains and the archaeological findings from Münsingen were subject of many investigations (Alt et al. 2005; Kutterer and Alt 2008; Müller 1998; Scheeres et al. in press; Uerpmann 2005). Investigations also included biomolecular analysis to answer questions about genetic relations, but the analysed samples contained insufficient traces of DNA. Therefore, research on epigenetic characteristics and hereditary skull deformations was performed to assess possible biological relationships in the population (Kutterer and Alt 2008). While some skulls may appear to be deformed, even the anthropological measurements do not rule out the possibility that the deformation could be the result of taphonomical processes during burial time. The skull deformations as an indicator for genetic relationship therefore remain questionable.

The extensive archaeological material from the burial site of Münsingen also raised questions concerning migration and origin of the individuals. On the one hand, some subadults were buried with grave goods that were normally used for adult females. On the other hand, some burials contained incomplete jewellery sets or no grave goods at all (Sankot 1980). The position of all objects, especially fibulae, rings and bracelets, allowed a reconstruction of the attire of Iron Age

women. Furthermore, the position of weapons such as swords and lances in male graves suggested how they might have been carried (Wyss et al. 2002). In some graves, traces of wooden coffins and stone settings were found (Müller et al. 2008).

Stable isotopes

Several studies on Iron Age human bones have been conducted, e.g. in Croatia (Lightfoot et al. 2012), the Czech Republic (Le Huray and Schutkowski 2005), Germany (Oelze et al.

2012), Great Britain (Jay and Richards 2006; Stevens et al.

2013), Greece (Papathanasiou et al. 2013), Russia (Murphy et al. 2013) and Sweden (Howcroft et al. 2012). So far, hardly any isotope analyses on human bones have been carried out in Switzerland, with the exception of Tütken et al. (2008). A short review of stable isotope values from some Iron Age burial sites in central Europe is shown in Table 1.

The analysis of the carbon stable isotope ratios in bone collagen sheds light on the input of C3 or C4 plants in the diet (DeNiro and Epstein 1978). Due to different photosynthetic pathways, C3 and C4 plants exhibit different Ö13C values (Ambrose 1993; Hoefs 2009; Lee-Thorp et al. 1989). Stable carbon isotope ratios of C3 plants such as wheat and barley show values between -19 and -35 %o. 613C values ofC4 plants such as millet and amaranth are between -9 and -15 %o (Ambrose 1993). In each trophic level of the food chain (prey to predator collagen), the Ö13C (13C/12C) value is enriched by + 1 %, whereas the fractionation factor between plants and bone collagen is 5 % (Redfern et al. 2012).

Stable nitrogen isotopes Ö15N (15N/14N) in bone collagen reflect the intake of animal protein like meat and dairy products (Ambrose 1993; Stevens et al. 2010). The Ö15N value

Fig. 2 Grave numbers with illustration of horizontal spread in the ► greyscale (earlier phase = black; later phase = white), possible immigrated individuals are marked in green (modified after Hodson 1968)

increases towards the top of the food chain in an ecosystem; hence, nitrogen stable isotope ratios provide information about the trophic level. Due to biological fractioning, the approximate shift between trophic levels is about +3 to +5 % in bone collagen (Bocherens and Drucker 2003; Hedges et al. 2007). Terrestrial plants generally have 4 % lower ö N values than marine plants, and marine animals have higher ö15N values than terrestrial animals due to the trophic level effect with more trophic levels in marine than in terrestrial ecosystems. Therefore, nitrogen isotopes can not only be used to analyse the relative contribution of animal and plant food but also of terrestrial and marine resources (Schoeninger 1984).

A multiple isotopic approach with analysis of sulphur isotope ratios in addition to carbon and nitrogen provides more information about ancient populations' nutrition (Vika 2009). ö34S (34S/32S) in bone collagen is passed along the food chain with a small fractionation of approximately -1 %. The ö34S values in freshwater and terrestrial ecosystems range from -22 to +22% (Oelze et al. 2012; Privat et al. 2007). Terrestrial mammals have ö34S values lower than +10 %, whereas organisms in marine ecosystems have values around +20% (Nehlich et al. 2012; Richards et al. 2003). In addition, variations in sulphur isotope data could provide information about migration of individuals. They vary in different geographical regions and geological conditions (Vika 2009). Until now, there are some publications about ö34S in ancient bone collagen (Craig et al. 2006 Fornander et al. 2008; Hu et al. 2009; Kinaston et al. 2013 Nehlich et al. 2011; Nehlich et al. 2012; Oelze et al. 2012 Privat et al. 2007; Richards et al. 2003; Vika 2009).

For long bone cortex, a turnover rate of approximately 10 to 15 years is published (Hedges and Reynard 2007; Jay and Richards 2006), whereas the turnover rate for the skull is known to be approximately 50 years (Rummel et al. 2007). Therefore, the obtained signature reflects the diet during the individuals' last decades of life.

Stable isotope analyses (C, N, S) were applied to reconstruct diet, social stratification and migration of individuals (Ambrose and Norr 1993; Lösch et al. 2006). The aim of this study was to reconstruct special diet restrictions of individuals from Münsingen including sex- or age-related variability of diet. A further goal was a chronological analysis and a correlation of the results with archaeological findings. In order to obtain information about an individual's social status, not only the presence or absence of grave goods can be used as an indicator (Härke 2000). Different studies already assessed status-related diet within a population by linking stable isotope values to archaeological data such as grave goods, location of graves or burial types (Jay and Richards 2006; Kinaston et al. 2013; Le Bras-Goude et al. 2013; Le Huray and Schutkowski 2005; Linderholm et al. 2008).

Table 1 Isotope data from human bones in Iron Age Europe

Study Burial site Period n Stable isotope values (mean and SD) s13C [%»]v-PDB s15N [%o]air s34S [/o]v

This study Münsingen (CH) Late Iron Age 63 -19.5±0.7 8.8±0.5 1.0±2.2

Jay and Richards (2006) Wetwang Slack (UK) Late Iron Age 61 -20.5±0.3 9.6±0.5 -

Lightfoot et al. (2009) Yarnton (UK) Late Iron Age 31 -20.1 ±0.3 10.9±1.1 -

Lightfoot et al. (2012) Different sites in Croatia Late Iron Age 60 -19.0±0.8 9.3±0.9 -

Le Huray and Schutkowski (2005) Kutnä Hora-Karlov, Late Iron Age 87 -18.9±0.5 9.8±0.6 -

Radiovesice I and II (CZ)

Knipper et al. (2014) Glauberg (G) including Early Iron Age 24 —18.2± 1.3 9.5±1.8 -

the "princely seat"

Oelze et al. (2012) Magdalenenberg (G) including Early Iron Age 50 -19.7±0.4 9.6±0.8 3.5± 1.5 (n

the "princely seat"

Material and methods

From the original 220 abundantly equipped burials, the skulls of 77 individuals and some postcranial bones are still preserved today. For the statistical analysis, three different groups (LTA, LTB and LTC) were formed for the analysed individuals based on the relative chronology established by Stöckli (1975), Hodson (1998) and Jud (1998).

The remaining skeletal material from Münsingen is housed in the Archaeological Service of Bern, and five skulls are exhibited at the Natural History Museum in Bern, Switzerland. One individual is only represented by the mandible. Due to conservational reasons, samples of only 71 individuals were taken for stable isotope analyses. Bone material was obtained mostly from skulls and some long bones (online resource Table 2).

Morphologic-anthropological investigation

A morphologic-anthropological description of the bones was provided in a catalogue (Hug 1956). Due to methods that were developed in the last decades, the human remains were reinvestigated for this study. The individuals' sex and age-at-death were determined using current methods (Ascädi and Nemeskeri 1970; Ferembach et al. 1979; Herrmann et al.

Table 2 Definition of

the age classes Age class Yea's

Infants I 0-6

Infants II 7-12

Juvenile 13 -20

Adult 20-40

Mature 40-60

Senile 60+

1990; Rösing et al. 2007; Scheuer and Black 2000; Sjovold 1988; Szilvässy 1988). For statistical tests, individuals were assigned to different age classes (Table 2).

Stable isotope analysis

Bone samples were cleaned with distilled water and ground to powder (n = 71). The collagen extraction followed the Ambrose (1993) and Longin (1971) procedure at the Department of Physical Anthropology at the University of Bern, Switzerland.

Five hundred-milligram bone powder was treated with 1 M HCl to dissolve the bone mineral and then rinsed until neutral. To remove humic acids, the samples were treated with 0.125 NaOH and gelatinized in 0.001 M HCl at 90 °C for 17 h. Then, the samples were filtered and freeze-dried. The lyoph-ilized collagen was weighed in tin capsules (3x), and the mean ofthree measurements was calculated. Stable isotope ratios of carbon (13C/12C), nitrogen (15N/14N) and sulphur (34S/32S) were analysed by isotope ratio mass spectrometry (IRMS at Isolab GmbH, Schweitenkirchen, Germany). All data are presented in S-notation in per mil (%o) according to international standards for carbon (Vienna Pee Dee Belemnite, VPDB), nitrogen (Ambient Inhalable Reservoir, AIR) and sulphur (Canyon Diablo Troilite, CDT) (Fry 2006; Hoefs 2009; Schoeninger 1984). An internal standard was used for determination of the analytical error. It amounted to ±0.1 %o for S13C, ±0.2%% for S15N and ±0.3 %% for S34S.

The collagen quality was verified as per Ambrose (1990), Ambrose (1993) and DeNiro (1985). Collagen with less than 1 % in proportion to the dry weight and samples with a molar C/N relation beyond a 2.9-3.6 range were not taken into consideration. Furthermore, %C and %N values that strongly diverge from recent collagen values (C 43 % and N 15-16%) were not analysed.

Statistical tests

All statistical tests were performed with SPSS Statistics 20. The robust Ttest for independent groups (two parameters) and the one-way ANOVA (three or more parameters) were used to determine significant differences between groups. Additionally, the non-parametric Mann-Whitney U test (two parameters) and Kruskal-Wallis test (three or more parameters) for independent samples were used due to the small sample size as normality is not given for all groups (Fagerland 2012). The level of significance is indicated with superscript stars on thep values: p<0.05 (*);p<0.01 (**); and p< 0.001 (***).

Results

After applying the quality criteria, 63 of 71 collagen samples remained for the analysis of stable carbon, nitrogen and sulphur isotopes (27 males, 29 females, 7 infants). All data will be shown with individual numbers because some graves contained more than one individual. For corresponding grave numbers, see online resource Table 2.

All 534S values were evaluated for this study, except the samples that were excluded due to the aforementioned collagen quality criteria. Descriptive statistics for carbon, nitrogen and sulphur stable isotope ratios for all individuals (n=63) are shown in Table 3.

513C values range from -20.8 to -17.4%o (mean -19.5%0; standard deviation (SD) 0.7%o), those of 515N range from 7.6 to 10.2%0 (mean 8.8%0; SD 0.5) and 534S values range from -2.3 to 7.6%0 (mean 1.0%0; SD 2.2%0).

The one-way ANOVA showed significant differences between the 5 C (p=0.022*) and 5 N mean values (p= 0.005**) of males, females and infants but no significant difference for 534S mean values (p=0.198). The infant I and II age groups were excluded by testing only males and females. In this case, the T test for independent groups revealed significant differences between 513C and 5 15N mean values (p for 513C=0.007**, 515N=0.00 6**, 534S=0.686). Non-

parametric tests showed also significant differences between the sexes (Table 4).

No significant difference between the different age classes (infants I and II, juvenile, adult, mature, senile) can be observed (one-way ANOVA). Non-parametric Kruskal-Wallis test showed significant differences in the 515N values between the different age classes (p=0.030*).

Forty-three of 63 individuals could be assigned to a chronological group (Table 5). For the LTB period, no infants were available for analysis. One-way ANOVA revealed no significant differences, while the 513C values are significant different by using the non-parametric Kruskal-Wallis test for independent groups (Table 4).

The analysed samples were also subdivided into two groups according to the presence or absence of grave goods (online resource Table 2). Forty-seven individuals out of 63 were found with grave goods and 16 without (Jud 1998). The T test and the non-parametric Mann-Whitney U test for independent groups revealed no significant differences between these two groups (Table 4).

Discussion

Limitation of the study

It has to be mentioned that no animal bones from Münsingen or close by Iron Age burial sites were available for stable isotope analysis. The analysis of faunal remains can provide important information on the general status of the whole population, so human-faunal trophic level should be taken into consideration. Differences in the stable isotope values could be the result of various environmental factors and/or different methods of animal husbandry (Stevens and Hedges 2004; Ugan and Coltrain 2011). Therefore, a comparison of the diet of the Münsingen population with published data from other geographical regions is hardly possible. There are a few faunal remains from the Iron Age burial site of Engehalbinsel, but they are not dated yet. These remains were not available during the analysis of the Münsingen material, but they are

Table 3 Descriptive statistics for carbon, nitrogen and sulphur stable isotope ratios (n=63, mean, standard deviation, median, minimum, maximum)

s13C [%»]v-pdb s15N [%»]air s34S [%»]v-cdt

n Mean SD Median Min Max Mean SD Median Min Max Mean SD Median Min Max

Male 27 -19.7 0.6 -19.9 -20.8 -18.5 9.0 0.5 9.0 7.6 10.2 1.3 2.4 0.8 -2.3 7.6

Female 29 -19.2 0.7 -19.2 -20.5 -17.4 8.6 0.5 8.7 7.6 9.5 1.0 2.1 0.3 -1.2 6.4

Infants I and II 7 -19.6 0.6 -19.3 -20.5 -19.0 8.5 0.3 8.6 7.9 8.8 -0.4 1.4 -0.8 -1.7 1.6

Total 63 -19.5 0.7 -19.6 -20.8 -17.4 8.8 0.5 8.8 7.6 10.2 1.0 2.2 0.4 -2.3 7.6

SD standard deviation

Table 4 Results of statistical tests

Different groups n Variables T test or one-way ANOVA (p) Mann-Whitney U or Kruskal-Wallis test (p)

Male vs. female vs. infants 27; 29; 7 S13C 0.022* 0.035*

s15n 0.005** 0.003**

S34S 0.198 0.168

Male vs. female 27; 29 S13C 0.007** 0.011*

s15n 0.006** 0.006**

S34S 0.686 0.605

Male vs. infants 27; 7 S13C 0.554 0.617

s15n 0.012* 0.004**

S34S 0.090 0.081

Females vs. infants 29; 7 S13C 0.258 0.287

s15n 0.476 0.387

S34S 0.950 0.094

Age classes (infants I, infants II, juvenile, 1; 6; 3; 32; 12; 9 S13C 0.175 0.163

adult, mature, senile) s15n 0.083 0.030*

S34S 0.367 0.157

LTAvs. LTB vs. LTC 14; 21; 8 S13C 0.055 0.035*

s15n 0.809 0.877

S34S 0.292 0.251

With vs. without grave goods 47; 16 S13C 0.568 0.548

s15n 0.384 0.248

S34S 0.887 0.850

All individuals vs. armed males 54; 9 S13C 0.209 0.197

615N 0.014* 0.009**

S34S 0.291 0.326

Ttest for independent groups (two parameters) and one-way ANOVA (three or more parameters) were performed. Additionally, Mann-Whitney U test (two parameters) and non-parametric Kruskal-Wallis test (three or more parameters) for independent samples were used due to the small sample size *p<0.05, **p<0.01, ***p<0.001

subject of ongoing research and will be presented in future work.

Entire population—differences in sex and age

For a comparison of male and female data, the infant I and II age groups were excluded. The observed carbon isotope ratios of all individuals indicate that the subsistence bases in Münsingen were C3 plants such as wheat and barley. These cereals were not only used for solid food. In Hochdorf,

Table 5 Numbers of individuals assigned to the different time phases

Male Female Infants I and II Total

Time period LTA 4 6 4 14

LTB 11 10 0 21

LTC 2 6 0 8

No dating 10 7 3 20

Total 27 29 7 63

Germany, there is evidence of beer brewing during the early Iron Age (Stika 1996; Stika 2011). Palaeobotanical analysis showed that wheat and barley were the most common cereals in central Europe during the Iron Age. C4 plants were also found in the Iron Age Alpine region and southeastern France (Bouby et al. 2011; Jacomet and Jacquat 1999; Schmidl et al. 2007). However, the data in this study give no indication of a significant intake of C4 plants, although males in Münsingen show a more negative ö13C mean than females (Table ). ö 13C values more positive than —18%o lead to the suggestion of C4 plant consumption (Le Huray and Schutkowski 2005), as the presence of millet is known since at least the third millennium bc (Hunt et al. 2008; Motuzaite-Matuzeviciute et al. 2013). Lightfoot et al. (2012) suggest a minor consumption of millet in Iron Age Croatia (n=60). Le Huray and Schutkowski (2005) also published more positive ö C (mean —18.9±0.5 %o) for different Late Iron Age burial sites in the Czech Republic. They conclude that the more positive ö C values may reflect some contribution of C4 plants for at least some individuals. However, an increase of ö13C values could also

indicate a higher consumption of, e.g. seeds, fruits and roots (Cernusak et al. 2009). In Münsingen, the values of one female (A70) and possibly those of two other females (A102, A110) also point to an occasional consumption of C4 plants. The slightly depleted ö13C values of the males could also indicate a higher intake of (animal) products from boreal environments. Species that are endemic to forested habitats exhibit lower ö13C values than those from open land spaces (Bonafini etal. 2013; Drucker etal. 2008; Stevens etal. 2006). Even though the proportion of wild animal bones in settlements from this time and region is less than 2 % and therefore comparatively low (Schibler et al. 1999), it cannot be excluded that men spent more time in the forest and used its food resources more frequently. Eating these foods on the spot may also explain the largely absent wild animal bones in the settlement waste. Hunting or military excursions to neighbouring regions that lasted several days or weeks are a possible hypothesis. Likewise, the enriched ö13C values in females could be the result of them mostly staying in the settlement and subsisting on domesticated animal resources.

The ö15N values show differences between females and males, with males having significantly higher values than females (Table 4). This leads to the suggestion that there might have been gender restrictions in the access to animal proteins (meat and dairy products) and that males consumed more animal proteins. These differences in diet could be related to a gender-specific division of labour in which males were responsible for meat preparation. A more plausible explanation for the population of Münsingen is a higher social rank of male individuals that was accompanied by better access to animal protein. Even though there are statistically significant differences between males and females, it must be kept in mind that these differences are small (Fig. 3). This result is in line with past findings of animal bones only in male graves, even though there were also females with "high class" grave goods like the adult female A114 (Jud 1998).

The only senile female (A66) has a high ö15N value of 9.45 %o compared to the rest of the group as well. According to the illustrations of Wiedmer-Stern (1908),

10.5 10.0 9.5

1 90 2

8.0 7.5 7.0

□ J3 0.2

. . ITi+l -A oo

o ® * o< E>

A U □ n ° O

O female □ male & infants II

0 infants I

• mean females ■ mean males

1 mean infants

-19.0 613C(%o)

Fig. 3 Plot of S13C and S15N values for Münsingen human bone collagen samples with mean values and standard error bars (n=63)

this female can be dated to the LTA/LTB period, and no grave goods were found in this grave.

ö34S values indicate a strictly terrestrial diet with no intake of marine food. This is supported by the fact that no fish bones were recovered from this site (Jud 1998). It should be mentioned that it is not unusual to have no fish bones on a burial site due to poor preservation or excavation techniques used in the past. However, Dobney and Ervynck (2007) mention cultural or spiritual factors as a possible explanation for this phenomenon. In either case, access to marine food is naturally not expected for Münsingen. The stable isotope ratios do not provide evidence of an increased consumption of freshwater fish, even though a wide variability of the isotope values has to be considered (Katzenberg et al. 2012; Katzenberg 1999). It remains unclear why freshwater fish was apparently not used as an important resource even though the Aare River is nearby. Similarly, no exploitation of freshwater resources is suggested for the Iron Age burial site in Yarnton which is also close to a river (Lightfoot et al. 2009). It is assumed that marine fish was not often used as food resource in the British Iron Age (Dobney and Ervynck 2007). The burial site Wetwang Slack is nowadays located approximately 25 km from the coast, and the authors suggest a diet without marine foods (Jay and Richards 2006). Likewise, investigations of diet in Iron Age Croatia found no evidence of significant marine protein consumption in spite of the analysed burial sites being close to the coast (Lightfoot et al. 2012).

There are no significant differences between the age groups for ö13C and ö34S values. Lightfoot et al. (2009) investigated Iron Age individuals (n=31) from Yarnton, UK and found the highest ö15N values in infants (<3a). This result derives from a higher trophic level due to breastfeeding. Nursing babies consume mother's milk which is enriched with N (Bourbou et al. 2013; Burt 2013; Fuller et al. 2006; Katzenberg 2008; Katzenberg et al. 1996). In this study, only one child (A50) aged 3 to 5 years could be analysed for stable isotope ratios. Compared to other individuals, the ö15N value was relatively low (8.34%o). The infants in Münsingen show no breastfeeding signal. Due to the lack of infant I and the small number of infant II, the weaning time cannot be narrowed down. After excluding all infants, still no significant difference of ö N between the different age classes can be detected (one-way ANOVA; p=0.080). However, there is a tendency of senile individuals to be enriched with 15N by using the one-way ANOVA (p=0.083) and even a significant difference by testing with non-parametric Kruskal-Wallis test (p=0.030*). This might suggest that the oldest individuals had a higher proportion of animal protein in their diet. This tendency stands in contrast to results from Iron Age Yarnton where the opposite was observed (Lightfoot et al. 2009). Prowse et al. (2005) had similar results in their analysis of Imperial Roman human remains from the necropolis of Isola Sacra, Italy. Their results show a positive correlation between age and ö15N. The data of Prowse et al. (2005) indicate that

subadults consumed a more herbivorous diet. They suggest that maybe a suboptimal diet might have led to their early death. This could also be possible for Münsingen. However, it remains questionable if senile individuals lived longer because of an increased consumption of animal proteins or if older individuals had a higher social status in the community. For the comparison of age classes, it should be kept in mind that the determination of the age-at-death was based on morphological features on the skulls. Especially for adult and older individuals, this might have led to some uncertainties that could have influenced the statistical analysis. Manuring is also a possibility that has to be considered with regard to variations in stable nitrogen values between different burial sites (Bogaard et al. 2007). Human diets with a high component of manured grain lead to elevated nitrogen values and could therefore also be interpreted as a diet with a high amount of animal protein. This has to be considered for the Iron Age as there manuring practices were found in prehistory as well (Guttmann et al. 2006; Nielsen and Kristiansen 2014).

Mobility

The ö34S values of all infants (and juveniles) range between -2 and 2 %o. There is little fractionation of sulphur isotopes through food chains, and therefore, ö34S values of bone collagen reflect the local geological sulphate (Richards et al. 2001). Assuming that young individuals had few opportunities to travel, their ö S signal might best represent the local sulphur signal. Males and females with enriched ö34S could have lived at or near coastal areas at some point in their life (Fig. 4). Due to the so-called sea spray effect, the ö34S values might also reflect the proximity of the food source to the sea (Richards et al. 2003). Three males (A57, A62 and A65) and four females (A60, A70, A88 and A108) show enriched ö34S values above 4%o, and amigration to Münsingen could be possible for these individuals (Fig. 2, marked in green). Four of them (A57, A60, A62 and A70), two males and two females, were buried in the oldest part (LTA) and might belong to the "founder generation". The dating for two other individuals (A65 and A 88) is uncertain, and one

Fig. 4 Plot of s13C and s34S for Münsingen human bone collagen samples with mean values and standard error bars (n=63)

individual (A108) dates to the LTC period. One female aged 3050 years (A70) additionally shows an extraordinarily high Ö13C value (-17.4%%) and a relatively low Ö15N value (7.8%0). This female with a sulphur value of 4.4%o could either have had a different diet than the others or might have migrated to Münsingen from another region with more access to C4 plants. This woman was buried in the northern part (LTA to LTB) of the cemetery. Investigations of strontium and oxygen isotope ratios by Scheeres et al. (in press) also show minor mobility of the Münsingen population. For a better comparison, their data are used as individual numbers (grave numbers were used in the original publication). They analysed tooth enamel of 38 individuals for strontium isotope ratios and 34 individuals for oxygen isotope ratios. Their results indicate that two females from the LTA period (A43 and A60) immigrated to Münsingen. This is in accordance with the result for individual A60 in this study. Unfortunately, the possibly immigrated individuals A62, A65, A70, A88 and A108 in this study were not analysed by Scheeres et al. (in press). The authors suggest that five individuals (A43, A60, A67, A85 and A103) were not local due to the strontium and oxygen isotope values. The individuals A43, A67 and A103 could not be analysed in this study due to collagen quality criteria. Individual A85 shows no evidence of migration based on the stable sulphur value. Like what Scheeres et al. (in press) stated, this study could give an additional hint that the founder population in Münsingen mainly consisted of an existing local community to which both males and females immigrated from elsewhere. Whether the structure of the Münsingen population was patrilocal or matrilocal cannot be ascertained by the presented stable isotope values.

Chronology

Due to the clear horizontal spread of the Münsingen burials and the good documentation, 43 out of 63 individuals could be assigned to a chronological group. No significant differences of stable nitrogen and sulphur isotope values between three chronological periods of the Münsingen burials were found (Table 4). However, stable carbon isotope ratios show significant more positive values in later phases of the burial site compared to earlier phases (non-parametric Kruskal-Wallis test; p= 0.035*). This could indicate minor changes in vegetation and crops which is possible due to climate changes during the Iron Age in central Europe. Climate reconstructions from sediments of Lake Silvaplana in Switzerland indicate warmer trends in the Late Iron Age (Stewart etal. 2011). Palaeoglaciological analysis of fluctuations of the Great Aletsch glacier (Valais Alps) shows a minimum length of the glacier tongue between 200 bc and 50 ad for the Late Iron Age (Holzhauser et al. 2005). Due to postponed effect of climate on the glacier, a time lag of a few decades can be assumed. Warmer climate probably would have led to increased growth of C4 plants such as millet which prefer warmer ecosystems (Ehleringer et al. 1991; Satrapovâ et al. 2013). This

could be a possible hypothesis for the more positive ö13C in the LTC period. While there is no evidence for a significant C4 plant intake in Münsingen, a minor consumption of, e.g. millet in the later phases has to be considered.

Grave goods

The burials varied in their content of archaeological findings from those with many grave goods to those with none (online resource Table 2). Some grave goods such as weapons, meat and gold finger rings were only given to adult and older males. No significant differences between the individuals with and those without grave goods were obtained. Nevertheless, in 18 male burials, items of weaponry were found, particularly swords in 12 male burials but also lances and shields (Jud 1998). Weapons, especially swords, are usually considered to be prestige grave goods and a symbol for a higher status (Linderholm et al. 2008). Ten of the "armed" males from Münsingen were available for the stable isotope analysis, but A47 was excluded due to collagen quality criteria. The ö13C and ö34S values of the remaining nine males (A58, A72, A78, A80, A81, A84, A95, A100 and A117) show no significant differences in comparison to all other individuals. But the ö N values show significant differences with higher values in the males buried with weapons (Table 4). These results indicate increased access to animal protein for the "armed" males. Analysis of Iron Age populations in Bohemia also showed different dietary patterns with higher ö15N values for some male individuals buried with weapons (Le Huray and Schutkowski 2005). The ö34S values of these nine males are very heterogenic and vary between -2.0 and 2.7%o. None of them indicate a possible immigration to Münsingen.

Meat as a possible prestige grave good was probably given exclusively to males as it was only found within male graves (Jud 1998). Four individuals (A72, A75, A78 and A80) with meat as grave goods were available for stable isotope analysis (see online resource Table 2, marked with circles). The adult male A80 shows the highest ö15N value with 10.23 %0. This individual was buried with weapons and meat. The high ö15N value strongly suggests a diet with more animal protein than the other individuals. He might have played a special role in the society, and it is possible that he had privileges due to a high status. Oelze et al. (2012) published isotope values of 50 individuals from Early Iron Age Magdalenenberg, Germany. The Magdalenenberg tumulus contained a "princely burial" which was represented only by a long bone due to early grave robbing and some other adult male individuals which were characterised as high status "warriors". They also showed a different diet than the other individuals in the tumulus. Iron Age populations from the Czech Republic (Le Huray and Schutkowski 2005) and burial sites in Germany (Knipper et al. 2014) show evidence of a different diet of males buried with weapons, as well. These data in summary indicate a

higher social status for the Iron Age "warrior" burials assuming that the availability of meat or dairy products was probably restricted.

Furthermore, it has to be mentioned that isotopic variations in Europe are not only caused by cultural, biological and environmental factors but probably also correspond to regional differences in climate (Van Klinken and Hedges 2000). For this reason, comparisons of stable isotope values from different regions in Europe have to be carried out carefully.

Conclusion

The carbon isotope ratios indicate that the subsistence base ofall individuals in Münsingen were C3 plants. The ö13C and ö15N values show significant differences between the sexes. There might have been a gender restriction in the access to food, especially animal proteins. The data also indicate a tendency towards a different diet of adults and seniles, with the diet of the latter probably containing more animal protein. ö S values show no significant intake of marine and freshwater fish for most of the individuals. The results also indicate that the founder population of Münsingen consisted mainly of an existing local community to which a few individuals—two females and two males—immigrated. A trend in ö C values of the different chronological phases leads to the suggestion that a change in diet took place in the later phases. A possible explanation could be a climate change during the occupancy time of the cemetery (LTA to LTC) that caused a change in vegetation. No differences between the individuals with grave goods and those without could be observed. However, the data lead to the suggestion that males buried with weapons might have played a special role in the Iron Age society of Münsingen.

Acknowledgments We are very grateful for the helpful comments of the reviewers. We thank Andreas Rossmann for stable isotope measurements, Christine Cooper for editing, Marc Nussbaumer and the Archaeological Service of the Canton of Bern for support. We also thank Silke Schleiss for assistance in the laboratory, Matthias Dömötör for image editing and Domenic Rüttimann for helpful comments. This project was funded by the Swiss National Science Foundation (CR13I3_149589).

Open Access This article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution, and reproduction in any medium, provided the original author(s) and the source are credited.

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