86Sr range for archaeological skeletons: a case study from Neolithic Europe

Journal of

Archaeological SCIENCE Journal of Archaeological Science 31 (2004) 365–375 http://www.elsevier.com/locate/jas

Determining the ‘local’ 87Sr/86Sr range for archaeological skeletons: a case study from Neolithic Europe R. Alexander Bentley a,*, T. Douglas Price b, Elisabeth Stephan c a

AHRB Centre for the Evolutionary Analysis of Cultural Behavior, Institute of Archaeology, University College London, 31–34 Gordon Square, London WC1H 0PY, UK b Laboratory for Archaeological Chemistry, University of Wisconsin, 1180 Observatory Drive, Madison, WI 53706-1393, USA c Landesdenkmalamt Baden-Wu¨rttemberg, Archa¨ologische Denkmalpflege, Silberburgstr. 193, 70178 Stuttgart, Germany Received 19 March 2003; received in revised form 31 July 2003; accepted 2 September 2003

Abstract Measurement of strontium isotopes in archaeological skeletons is an effective technique for characterizing prehistoric mobility. However, interpretation of the results can be highly sensitive to small changes in the determined ‘local’ 87Sr/86Sr signature at an archaeological site. Because the local range is often defined as within 2 s.d. from the mean 87Sr/86Sr value in archaeological human bones, the susceptibility of bones to diagenesis may lead to significant overestimates in the number of ‘non-locals’ at a particular site. Tooth enamel, on the other hand, is highly resistant to postmortem biochemical alteration, and it is found that 87Sr/86Sr in archaeological enamel samples from animals of Neolithic Germany provide a useful alternative estimate for the local range.  2003 Elsevier Ltd. All rights reserved. Keywords: Strontium; Neolithic;

87

Sr/86Sr; Migration; Human mobility

1. Introduction: isotopic evidence from skeletons Over the last two decades, the measurement of strontium isotopes in archaeological skeletons has matured into an established method for characterizing prehistoric mobility (e.g., [6,10,11,16,32,33,37,42,46]. Strontium isotopes have revealed aspects of settlement and migration patterns of Neolithic Bell Beaker people in Europe [15,32,34], of historic South Africans [43], of the ‘Iceman’ [18], in Mesoamerica [35], and in the prehistoric US Southwest [12,33]. The theoretical basis, practical method and potential complications of this technique have been discussed in a number of publications (e.g. [8,10,20,21,32,36,42,46]). In principle, the method works quite simply. Different rocks are characterized by distinct ratios of two isotopes of strontium, 87Sr and 86Sr. As rocks weather into soils, the plants growing in those soils acquire the 87Sr/86Sr ratio. Animals that eat the plants incorporate strontium * Corresponding author. Tel.: +44-20-7679-4730; fax: +44-20-7383-2572. E-mail address: [email protected] (R.A. Bentley). 0305-4403/04/$ - see front matter  2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.jas.2003.09.003

(which substitutes for calcium in the mineral structure) into their skeleton, as do carnivores who eat those animals. Because Sr is a high-mass element, the difference between the two isotopes is relatively small, and there is negligible fractionation, i.e., change in the 87 Sr/86Sr ratio, as strontium passes from weathered rocks up the food chain into the human skeleton. Beard and Johnson [2] point out that even if there were a slight fractionation in 87Sr/86Sr on the way from rocks to skeletal tissue, it would be corrected for upon mass spectrometry by a routine normalization to the value of 86 Sr/88Sr, a natural constant conventionally assumed to be equal to 0.11940. Hence the 87Sr/86Sr ratio in skeletal tissues reflect all of the foods in the diet at the time of their formation or remodeling. 1.1. The problem: what is the local

87

Sr/86Sr range?

As with any archaeometric technique, with maturity and more widespread application come the complications. The purpose of this paper is to discuss the problem of determining the ‘local’ strontium isotope signature for a particular archaeological site. In several

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studies (e.g. [4,15,33]), it has been the practice to define a ‘local’ tooth value as within 2 s.d. of the average human bone value. Although this is seen as a conservative definition unlikely to make an incorrect non-local identification, it is still a subjective partitioning of the data rather than an objective representation of rigid isotopic ‘boundaries’ on the prehistoric landscape. In order to better define the ‘local’ range at a particular site, we confront three main questions [37]: (1) What does a ‘non-local’ or ‘local’ strontium isotope signature mean for the prehistoric individual, (2) how do we minimize the ‘noise’ caused by post-burial contamination, and (3) how do we control for the natural variation of strontium isotope signatures in rocks, water sources and plants? The first issue is that of what ‘local’ and ‘non-local’ imply for the prehistoric individual. Technically, an enamel 87Sr/86Sr value that is outside an analytically defined local range only implies that that person once ate foods which came largely from non-local sources. The strontium isotope signature in teeth and bone does not simply record a person’s migration from Place A to Place B, but rather a more complicated signature of multiple diet catchment areas that includes the places a person visited, as well as potentially non-local places where food was pastured or grown. For this reason we prefer to use the term ‘non-local’ rather than ‘immigrant’. This distinction can be seen as an asset rather than a liability of the technique, as it may be possible to identify individuals whose subsistence activities took place over a diverse range of territories. The second issue is diagenesis—the tendency for groundwater strontium to penetrate the skeleton after burial and overwhelm or even replace the in vivo strontium in its mineral portion. Diagenesis is practically inevitable in buried archaeological bones (e.g., [9,19,25,28–30,49]), with the rate of degradation apparently dependent on the porosity of the bone [40]. Diagenetic strontium can often be removed by proper sample cleaning such as with weak acid (e.g. [29,31,33,42,45]), but in some cases it cannot [19], especially if the original biological strontium has been completely replaced after burial [6,20,39]. Grupe et al. [15] and Grupe et al. [16] argue that this ‘contamination’ in any case would be local, since it is derived from the groundwater solution. An important question is whether ‘local’ contamination might reduce the original variation in the human bone 87Sr/86Sr values, which would narrow the local range as defined by the standard deviation of those values [21]. Fortunately, a large amount of circumstantial evidence suggests that tooth enamel retains an in vivo strontium isotopic signature, even in samples thousands or hundreds of thousands of years old. Tooth enamel contains larger mineral crystals and is much less porous than bone, and is highly resistant to

biochemical alteration with respect to 87Sr/86Sr (e.g., [6,8,17,19,20,36,44,48]. This means that meaningful patterns can be found by comparing the 87Sr/86Sr values of prehistoric human teeth with relevant archaeological evidence—such as sex and age of the skeleton, burial position and artifacts in the grave—even if the human bones are not well enough preserved to define a local range for the burial site. The third issue concerns the environmental heterogeneity of strontium isotope signatures, which vary in the different minerals of a single rock, in the leaves, stems and roots of a plant, or in water sources such as streams and precipitation [37,46]. Hence, while initial estimates of the local range may be derived from geological maps and indicators such as 87Sr/86Sr in stream waters, a more detailed mapping requires measurement of the different 87Sr/86Sr ratios in a variety of geologic materials, along with their Sr concentrations and weathering rates, in order to estimate the biological 87 Sr/86Sr ratio for a local area [2,20]. Fortunately, it is simpler and more direct to measure 87Sr/86Sr in local herbivore materials such as mouse bones or snail shells since, through a lifetime of feeding, herbivores obtain a remarkably consistent average 87Sr/86Sr ratio representative of their catchment area [7,37]. Modern herbivores will not often be useful, however, because they consume strontium from anthropogenic, non-geologic sources such as fertilizers and polluted rain, which are significant even (for example) in fairly remote uplands of France [38]. Considering all these issues, it appears that the best way to characterize the local strontium isotope signature at an archaeological site would be to measure the archaeological teeth of an animal species that lived locally [37]. This strategy minimizes the problems of environmental variability (as the animal acquires an averaged signature from the area), modern anthropogenic strontium, and diagenesis (to which tooth enamel is resistant). The remaining difficulty is that one may not know a priori which, if any, animals lived locally at a prehistoric site. Hence, there are two purposes for measuring strontium isotopes in tooth enamel from archaeological animals: to characterize the mobility of different species of interest, and to find the species the best represents the local signature of the site so that we can better interpret our results from animal and human skeletons. In the remainder of this paper, we present a case study concerning the importance of the local range determination. Revisiting the data from our previous studies of Neolithic Europe, we show how, for different human cemetery sites, the non-local signatures may or may not be separated from the local signatures, and how estimating the number of non-locals at a site can be highly sensitive to small changes in the local range determination. In a subsequent section, we describe our

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367

Fig. 1. Map of Neolithic sites mentioned in the text, along with the approximate extent of the Linearbandkeramik about 5300 BC. After Bentley et al. ([4]: Fig. 1).

measurements of archaeological animal tooth enamel from Vaihingen, a well-documented early Neolithic settlement, and we explore how our interpretations would change if animal teeth were used to define the local range, previously defined using the human bone values at this site. 2. An example of the importance of the local range: 87 Sr/86Sr in human skeletons from early Neolithic cemeteries in Germany We have recently measured strontium isotopes in human skeletons from the early Neolithic cemeteries of Flomborn, Schwetzingen and Dillingen in southwestern Germany [4,36], with locations shown in Fig. 1. The results have identified individuals with ‘local’ 87Sr/86Sr values, characteristic of the lowlands of the Upper Rhine Valley, as well as higher, ‘non-local’ 87Sr/86Sr values tending toward those of crystalline uplands within 50–100 km of these sites, including the Odenwald, Vosges and Black Forest [4,36]. Among skeletons with ‘upland,’ non-local signatures, females are common, and very few of the non-locals, male or female, were buried with a shoe-last adze, a characteristic early Neolithic artifact that was common with most of the males with local strontium isotope signatures [4]. If our interpretations are correct, these results intriguingly suggest that a socially distinct group of individuals, the majority of whom were female, settled with lowland agricultural communities after having lived a life that included

substantially more time in the uplands. One can imagine many possibilities—perhaps foragers married into Neolithic communities, or perhaps specialized stockherders, as a social group distinct from local cultivators, herded their livestock into the uplands ([4,5,50]:162). In any case, we rely on our definition of the local range to estimate the number of non-locals at each site (Table 1), which Price et al. [36] defined as the mean 87 Sr/86Sr in human bones plus or minus 2 s.d. at each site. How the local range is defined is a critical issue. If the range of human bone values has been compressed by diagenetic contamination, the estimates in Table 1 may reflect an overestimation of non-locals. Before using archaeological animal teeth to help determine the local range, we can first look more closely at (1) how sensitive the number of non-locals identified is to the way in which the local range is determined, and (2) the distribution of 87Sr/86Sr values in human bone at each site compared with the tooth enamel values, to see if modes exist that may correspond to local and non-local signatures. The latter allows us to consider whether the mode in the bone values may have been shifted by diagenesis. 2.1. The geologic setting The geologic setting of southwestern Germany and how it relates to the strontium isotope results has been described by Price et al. [36] and in further detail by Bentley et al. [5]. Basically, the lowlands of this area in southwestern Germany, as well as the Stromberg

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Table 1 Numbers of non-local humans at early Neolithic cemeteries of southwestern Germany, as identified by 87Sr/86Sr values in tooth enamel that fall outside 2 s.d. of the average human bone value at each site. After Price et al. [36], but with additional newer data from Schwetzingen [4] Site

Average 87Sr/86Sr in human bones

No. bones

Non-local teeth, male

Non-local teeth, female

Non-local teeth, ?

Total non-locals

Flomborn Vaihingen Dillingen Schwetzingen

0.709950.00017 0.709590.00022 0.708650.00012 0.709410.00036

6 25 7 7

2 3 6 4

4 2 5 5

1 9 0 2

73% 31% 65% 28%

of of of of

3 (67%) 11 (27%) 12 (50%) 18 (22%)

of of of of

4 (100%) 10 (20%) 5 (100%) 16 (31%)

of of of of

4 (25%) 24 (38%) 0 5 (40%)

Table 2 Sr isotope compositions in various materials from areas around Vaihingen. Bentley et al. ([5]: Table 1) provide a more complete version of this table Area

87

Sr/86Sr range n

Lowlands without loess

0.7075–0.7095

>40

Lowlands, loess areas 0.708–0.710 Plains, foothills 0.709–0.710 Uplands (Odenwald, Vosges, Black Forest) 0.7094–0.725

39 62 >130

External/anthropogenic

11

0.710–0.712

Mountains and Swabian Jura, are characterized by 87 Sr/86Sr ratios between about 0.708 and 0.710, based on measurements of rocks, streams and groundwater (Table 2). Consistent with this, the 87Sr/86Sr values in archaeological human bones from the lowland LBK sites of Dillingen to the east of Vaihingen and Flomborn and Schwetzingen to the west are all below 0.710. In contrast, the crystalline mountains in the region, including the Odenwald, Vosges and Black Forest, exhibit 87 Sr/86Sr above about 0.714; additional data from and modern shells and archaeological bones reiterate this difference between lowlands and uplands (Table 2). The upland–lowland difference in 87Sr/86Sr conveniently allows us to relate the strontium isotope signature in a Neolithic human tooth to how much of the diet the individual obtained from the uplands. Given hypothetical diets for foragers and farmers in Neolithic southwestern Germany [14], and the average Sr/Ca values in those foods [7], we can attempt to quantify the relative time spent in the uplands based on the 87Sr/86Sr values in tooth enamel ([5]: Tables 5 and 6). Of course, before we can begin to use such calculations reliably, the regional 87Sr/86Sr values must be well understood, which is difficult because (1) the geology of southwestern Germany is complex, (2) the archaeological human bones, though cleaned in weak acid, may still have contained diagentic strontium, and (3) the sampling of modern herbivores does not solve the problem because we do not know how much Sr from modern fertilizer and pollution has entered their diets. In order to properly map the Neolithic 87Sr/86Sr signatures of southwestern Germany, more data from

Material

Reference

Ground and river water, soils, LBK human bones, modern mice LBK and Bell Beaker human bones, modern snails and mice Stream water, modern snails Stream water, soil solutions, gneisses, granites, Triassic sandstones, LBK human bones Precipitation

[15,47] [5,15,37] [5,47] [1,5,38,47] [38]

pre-modern animals and people are needed. Recently, Schutkowski [41] reported an average 87Sr/86Sr ratio of about 0.7118 in tooth enamel from medieval miners of the Black Forest near Sulzberg. This is encouraging as, considering lowland values are around 0.709–0.710, the Sulzberg tooth value is close to that for local upland water (0.7138 [41]), and that for fish and animal snail shells (0.71110.0009 [5]) from near Titisee in the Black Forest. Building a database of these archaeological tooth enamel values from around the Upper Rhine valley is an ongoing project [22]. 2.2. Looking at the distributions of bone and tooth values We now revisit the 87Sr/86Sr data from human skeletons at Flomborn, Schwetzingen and Dillingen. We would expect that a histogram of the human bone 87 Sr/86Sr values from one site would exhibit a normally distributed mode that corresponds to the local range. Similarly, the tooth enamel values should also exhibit a mode for locals, but also values for non-locals. If the 87Sr/86Sr values in enamel are clustered in other modes, rather than continuously distributed, this supports the case for a real difference between non-locals and locals, as opposed to a continuum of diagenetic histories. The results from Flomborn (n=11 enamel and 7 bone samples) are particularly interesting because having been excavated at the turn of century [23], the skeletons were not contaminated with modern fertilizers while they were underground, although air pollution was

R.A. Bentley et al. / Journal of Archaeological Science 31 (2004) 365–375

369

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Sr/86Sr values in Neolithic human tooth enamel and bones from (a) Flomborn (b) Schwetzingen and (c) Dillingen.

significant in the nineteenth century. One would hope that there would be some modality to the distribution of enamel values—one mode corresponding to the local range, and at least one other for non-locals. Fig. 2a and Fig. 3 show that such modes may exist for Flomborn, with a mode (0.7095–0.7100) that coincides with most of the bone values, and another group of enamel values (0.7115–0.7125) well above the bone values. One cluster of four 87Sr/86Sr values in the tooth enamel samples corresponds very well with the bone values and hence the local range. The clusters correspond to the non-locals and locals that Price et al. [36] identified.

At Schwetzingen (n=39 enamel and 6 bone samples), excavated in 1989 [3], there is a large cluster of tooth enamel 87Sr/86Sr ratios within the local range defined by the bones (Fig. 2b), but part of that cluster extends above the range. Although contamination from modern fertilizers may have lowered the Schwetzingen bone 87 Sr/86Sr relative to the enamel values, the bone values are still not as low as the range for fertilizers used in the Upper Rhine region of 0.7070 and 0.7085 [27]. Also, the 87Sr/86Sr in a few modern snails and mice, which probably are eating plants grown partly on modern fertilizers, are lower than the prehistoric human bones at both Flomborn and Schwetzingen (Fig. 3).

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Fig. 3. Scatterplot of the 87Sr/86Sr values (jittered for visibility) in Neolithic human tooth enamel and bones from Flomborn, Schwetzingen, Dillingen and Augsburg, along with values from modern snails and mice (crosses=bones; circles=teeth; squares=snail shells).

At Dillingen (n=17 enamel and 7 bone samples), the human tooth enamel values have a mode that is normally distributed around a slightly different average 87Sr/86Sr ratio (0.709140.00079) than the bones (0.708670.00012), as shown in Fig. 2c. As at Schwetzingen, this offset may be due to a small diagenetic component in the bones. The number of nonlocals appears highly sensitive to the upper value of the local range. Fig. 3 shows that a substantial portion of the enamel values fall above the local range defined by the Dillingen bones, even though the enamel values seem to be clustered. The problem is that one cannot determine whether the cluster represents a single, local origin, or multiple origins with similar Sr isotope signatures. If one were to use the average 87Sr/86Sr2 s.d. in modern snail shells from Dillingen (0.70784–0.70892) to define the local range, eight of the sixteen individuals would be identified as non-locals—three less than identified in Table 1. The average 87Sr/86Sr in the Dillingen snails (0.708380.00027) is close to the average human bone value. This may be because the local range is correctly defined by the human bones, but it could also indicate that both the archaeological human bones and modern snails are permeated with strontium from modern sources. Compared to Flomborn and Schwetzingen, the results at Dillingen and Augsburg are much more sensitive to the way we define the local range. However, while there is clearly some uncertainty in the amount of immigration at Dillingen, it is fairly certain that there are immigrants in the sample. At least the two highest 87 Sr/86Sr values from the Dillingen teeth must be from immigrants. One Dillingen female (Grave 2) and one male (Grave 23) with 87Sr/86Sr above 0.710 are definitely

different from the rest. The nearest areas of high 87Sr/ Sr ratios are the granite mountains of the Bavarian Forest [15], about 150 km to the northeast. Support for the higher immigration rate at Dillingen comes from the patterns shown above between the Sr isotope signature and the sex, burial orientation and associated grave goods for each individual [4]. Also, a closer view of the Dillingen enamel samples suggests a mode of values below 0.709, which is essentially equal to the upper cutoff value defined by the bones (0.70891), and one mode above 0.709 (Fig. 3). Given the uncertainty whether the locals are represented by one or both of these modes, a very conservative assessment is that there are anywhere between two (12%) and eleven (65%) immigrants in the Dillingen sample. However, because of the patterns with burial criteria and the bimodal distribution in tooth enamel 87Sr/86Sr values, the higher immigration figures are more probable. 86

3. Tooth enamel from archaeological animals and the local signature: a case study at Vaihingen We now turn to the issue raised in the introduction: how can 87Sr/86Sr in the tooth enamel of archaeological animals help to refine the local range defined by human bone values at an archaeological site? As mentioned above, we do not know beforehand which animal is most likely to have lived locally at a prehistoric site. In the case of Neolithic Europe, we can only suspect that Neolithic cattle, sheep and goats are more likely to have been ranged away from the site. Deer may have lived locally, browsing on local crops, but also may have been hunted and brought in from a distance. Perhaps pigs or dogs are the most likely to have lived locally. Hence our

R.A. Bentley et al. / Journal of Archaeological Science 31 (2004) 365–375

approach in this study is to assume that the animal that lived the most locally will display the narrowest range of tooth-enamel 87Sr/86Sr values. Assuming that this animal is not in some way ‘sub-local,’ i.e., having been fed a diet from an even more restricted area than within a few km radius of the site, then we can use its range of tooth enamel values as a basis for the local 87Sr/86Sr signature. Our study has been conducted with skeletal remains from the early Neolithic village of Vaihingen, in the Neckar Valley near Stuttgart, excavated since 1994 by Ru¨diger Krause and the Landesdenkmalamt BadenWu¨rttemberg [24]. Vaihingen was settled in the Earliest Linearbandkeramik era (ca. 5400 BC). The village was later encircled by a flat-bottomed ditch that was filled in around 5200 BC. We measured strontium isotopes in human skeletons from Vaihingen, and identified significantly more non-locals with tooth 87Sr/86Sr values above the local range buried in the fill of the ditch, as compared with those individuals buried alongside longhouses within the settlement [5]. As was the case for Flomborn and Schwetzingen, the highest 87Sr/86Sr values from human teeth at Vaihingen suggest those ‘non-local’ individuals obtained more of their diet from uplands than did the ‘locals’, as the crystalline uplands of the region, including the Odenwald, Black Forest, and (up the Enz River from Vaihingen) the Red Sandstones (Buntsandstein), which are derived from the Black Forest, which all have higher 87Sr/86Sr values than the lowland calcareous formations near Vaihingen [5]. Characterizing these local values from around Vaihingen is also a goal of Knipper’s [22] ongoing research. A surprising result from Vaihingen was that a small pilot sample of archaeological faunal teeth (from a cow, caprine, dog and deer), which we expected to help represent the local strontium isotope signature, actually showed a fairly wide range of 87Sr/86Sr values [5]. Another exciting result from Vaihingen is that the four overall lowest tooth values from the site were from children ([5]: Fig 6, Table 2). The enamel in a child’s tooth is not fully mineralized upon his/her death and is thus more prone to postmortem biochemical alteration [26]. However, the 87Sr/86Sr of these children’s teeth being quite different from the range of 87Sr/86Sr in human bones ([5]: Fig. 3), which are also prone to diagenesis, suggests the difference is meaningful. Were these children fed a special diet? Bentley et al. [5] speculated that perhaps the young children with the lowest tooth 87Sr/86Sr values were raised on cow milk, because the 87Sr/86Sr value from a single cow tooth was actually below the Vaihingen local range (defined as 2 s.d. from the average human bone value). The preliminary strontium isotope results from domestic animals at Vaihingen prompted us to analyze tooth enamel from a larger sample of domestic animals from

371

the site. Discussed below, the results show fascinating differences between different domestic species and the humans. 4. Samples and procedure Tooth enamel samples from 33 domestic animals were measured, including 14 cattle, 8 caprines, 10 pigs and one dog. These samples came from excavated pits within the Vaihingen settlement, as well as from outside the ditch perimeter. With the exception of a few samples previously prepared and analyzed at the University of North Carolina [5], samples for this study were prepared at the Institute of Archaeology at the University College London. Using a carbon steel surgical blade, the pulp and dentin (having clear color and texture difference from enamel) were removed from a portion of each tooth, leaving only a sample of intact enamel. Because enamel forms in a complex manner, with the oldest enamel found at the crown and the youngest at the cervical margin as younger and younger bands of enamel form parallel to the cervical margin (see [13]: Fig. 2), an effort was made to obtain a relatively large sample of enamel, about 20–40 mg, in order to recover its average composition. Both bone and tooth enamel samples were prepared and analyzed by the same procedure described by Bentley et al. [5], with the thermal ionization mass spectrometry (TIMS) taking place at the Southampton Oceanography Centre (SOC). A small modification to the procedure, during the 7–8 h washing in 5% acetic acid, is that we now rinse the samples in MilliQ H2O after the first hour and then place them again in fresh 5% acetic acid for the remaining 7 h; this is intended to lower the likelihood that dissolved Sr in the first hour’s leach solution would re-mineralize back into the sample (cf., [19,32]). The purified samples were analyzed at SOC on a VG-MicroMass Sector 54 TIMS, with a 2 V 88Sr beam using a multi-dynamic peak jumping routine for 150 ratios and corrected relative to 86Sr/88Sr=0.1194 using an exponential mass fractionation correction. Internal precision (standard error) for 87Sr/86Sr with this protocol is typically 0.00001. For each TIMS run of 18 samples, two measurements of the NBS 987 standard (adopted 87Sr/86Sr value of 0.710245) were included. Over the period of time of these analyses (which includes runs by other SOC geochemists), NBS 987 was measured as 0.71024320 (2 s.d., n=55). 5. Results and discussion The results from the domestic animal teeth are presented in Table 3. There is a clear difference in 87Sr/86Sr values the different species, not so much in their

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Table 3 Sr isotope results from the tooth enamel of domestic animals at Vaihingen Laboratory no.

Species

Tooth

Vai Vai Vai Vai Vai Vai Vai Vai Vai Vai Vai Vai Vai Vai Vai Vai Vai Vai Vai Vai Vai Vai Vai Vai Vai Vai Vai Vai Vai Vai Vai Vai Vai

sheep/goat dog cow deer pig sheep/goat pig cow sheep/goat cow sheep cow cow sheep/goat pig cow cow pig cow sheep/goat pig cow pig cow pig pig sheep/goat cow pig pig sheep/goat cow cow

tooth tooth tooth tooth maxillary M1 mandible dP3 mandible M3 mandible M1/2 maxillary M3 maxillary M1/2 mandible dP4 maxillary M1/2 maxillary M3 maxillary M3 mandible molar fragment maxillary molar fragment mandible dP4 mandible incisor maxillary M1/2? mandible premolar maxillary M3 premolar/molar mandible M3 maxillary mandible canine maxillary M3 maxillary premolar maxillary M1? mandible premolar/molar maxillary molar maxillary/mandible M1/2 maxillary/mandible premolar/molar mandible M1/2

3844 3984 3645 3984 4322 4492 4521 4613 4614 4617 4619 4625 4669 4916 4942 4979 4981 4997 5000 5012 5015 5025 5038 5119 5145 5149 5157 5261 5295 5389 5395 5421 5524

Vai 5542

cow

Age

(Sub-)adult infantile adult  adult  infantile  adult adult    infantile   (sub-)adult adult

Level

Befund

Location

1–2

18

adult subadult (sub-)adult adult subadult-adult  (sub-)adult   

1–2 1–2 1–2 1–2 1 1–2 1–2 1–2 1–2 1–2 1–2 1–2 1–2 1–2 1–2 1–2 1–2 1–2 1–2 1–2 1–2 1–2 1–2 1–2 1–2 1–2 1–2

2 22 5 H–J 3 K–E 4 4 G–H–E 37 D–N 8 A–B 13 Y–W–Z–A 11 5 16 A–B 12 A–B–C 3A–B 11 B–C 5 C–D 1 I-J 2 A–B 6 B–C 14 A–B 1 D–B–C 10 A–B 9 A–B 7 A–B 2 A–B 3 A–B 17 D–E

300980 255950 255980 255980 210960 210960 210960 210970 210960 240960 210000 240990 240990 240970 180950 240000 180940 240000 180960 180950 180950 180950 180000 180970 180000 150950 150950 150910 150970



1–2

3 A–B

150970

87

Sr/86Sr

s.d.

Lab

0.70998 0.70939 0.70892 0.70911 0.70948 0.70938 0.70980 0.70906 0.70892 0.70920 0.70976 0.70918 0.70880 0.70966 0.70952 0.70939 0.70885 0.70964 0.70921 0.70972 0.70922 0.70910 0.70942 0.71003 0.70933 0.70933 0.70947 0.70916 0.70941 0.70947 0.70999 0.70958 0.71093

0.00070 0.00080 0.00120 0.00070 0.00001 0.00001 0.00001 0.00001 0.00001 0.00002 0.00001 0.00002 0.00001 0.00001 0.00001 0.00001 0.00002 0.00001 0.00001 0.00002 0.00001 0.00001 0.00001 0.00001 0.00002 0.00001 0.00001 0.00001 0.00001 0.00001 0.00001 0.00001 0.00001

UNC UNC UNC UNC SOC SOC SOC SOC SOC SOC SOC SOC SOC SOC SOC SOC SOC SOC SOC SOC SOC SOC SOC SOC SOC SOC SOC SOC SOC SOC SOC SOC SOC

0.70940

0.00001

SOC

The Isotope Geochemistry Labs are UNC=University of North Carolina Geology Department, and SOC=Southampton Oceanography Centre. (dP: deciduous premolar; P or M: permanent premolar or molar; M1/2: first or second molar.)

average values, but in the variation (Fig. 4). The average 87 Sr/86Sr value in enamel from cow teeth is 0.70934 0.00056, from caprine teeth is 0.709610.00035, and from pig teeth is 0.709460.00017. The standard deviation in the pig enamel values is thus less than half that of caprines and cattle. This suggests that pigs were kept more locally than cows, sheep or goats. The 87Sr/86Sr value (0.70939) from the tooth of a dog, probably also an animal kept locally, falls within the range of values from the pigs. As Fig. 4 shows, the pig teeth have a smaller variance in 87Sr/86Sr values than the human bones from the site, which average 0.709580.00023. If the pigs were not fed some restricted diet, this has three major implications: (1) the pigs’ diet came from a smaller (or more homogeneous) area than the humans, (2) pigs appear to be a good species to use to define the local range at Vaihingen and (3) although they may have been altered by some degree of diagenesis, the variance in 87Sr/86Sr values in

the human bones is still larger than that of the local pigs and does in fact, as Grupe et al. [16] contend, provide a conservative determination of the local range that is unlikely to misidentify locals as being non-local. Furthermore, the high variation in the human bone values relative to the pig enamel suggests that a meaningful amount of in vivo signature was measured in the human bones. Of course, if the pigs at Vaihingen were fed some restricted diet of foods grown from a single area, these conclusions would not be supported. We can only say that this seems unlikely given no evidence for fences or restricted pens at Vaihingen (R. Krause, personal communication 2003), and the likelihood that pigs were fed in the forest in the vicinity of the settlements. Pigs often feed on human garbage and waste and thus might consume a diet similar to the humans. Defined as within 2 s.d. of the mean 87Sr/86Sr in the archaeological human bones, the local range at

R.A. Bentley et al. / Journal of Archaeological Science 31 (2004) 365–375



373

9DLKLQJHQDQLPDOV DOO1HROLWKLFH[FHSWPRGHUQPLFHDQGVQDLOV





6U 6U







0 RGHUQ&RZ&DSULQH PLFH VQDLO 

3LJ'HHU +XPDQ+XPDQ+XPDQ 'RJ ERQHWRRWKVWRRWKG

Fig. 4. Scatterplot of the 87Sr/86Sr values (jittered for visibility) in Neolithic human tooth enamel (from settlement=‘s’ from ditch=‘d’) and bones from Vaihingen, along with values from the tooth enamel of excavated Neolithic animals.

Vaihingen is 0.70914–0.71004. Using this local range, Bentley et al. [5] found 14 non-locals out of the 46 individuals (30%), nine below the local range, five above it. Four (18%) of these non-locals came from the 22 settlement burials, and ten (42%) were from the 24 sampled individuals (tooth enamel) from the ditch. Bentley et al. [5] thus determined that there were significantly (P=0.10) more non-locals from the ditch (42%) than from within the settlement (18%) at Vaihingen. Now we may ask, what if we use the 87Sr/86Sr values from the pig teeth to determine the local range rather than the human bone values? Two s.d. of the mean 87 Sr/86Sr in the pig enamel samples gives a range of 0.70913–0.70979 (dotted lines in Fig. 4). Applying this range to the human enamel values ([5]: Table 2), there are no additional non-locals below the range, but we do add five more above it, for a total of 19 non-locals out of 46 individuals (41%), which is significantly higher than the number using the human bones for the local range. In addition, using the pig teeth to define a narrower local range makes the difference between the ditch and settlement more striking. Fourteen (58%) burials from the ditch are now non-locals, including six (25%) below the revised local range and eight (33%) above it. From the settlement, there are now five (23%) non-locals, three (14%) below the revised local range and two (9%) above it. Now a ditch/settlement difference is clear: of the ten human enamel 87Sr/86Sr values above the pigs’ range, eight are from ditch burials.

6. Conclusion The lesson we take from this is that determination of a rigid local range for an archaeological site is a complex issue, especially when relying upon archaeological human bones, modern herbivores or geological materials, all of which are likely to provide different estimates. Furthermore, as we saw for Dillingen and Schwetzingen, the number of non-locals identified can be extremely sensitive to even small changes in the local range estimate. Because of this sensitivity, the local 87Sr/86Sr range as determined from archaeological human bone values should be compared to an independent estimate of the local, biologically available range of 87Sr/86Sr values during the prehistoric occupation of the site. We believe the best second estimate of the local range is 2 s.d. from the mean 87Sr/86Sr in tooth enamel from prehistoric animals that lived locally. Because it will not often be known a priori which animals did live locally, it is best to analyze tooth enamel from several animal species and choose the one with the narrowest range. Having noted the difficulty in determining the local 87 Sr/86Sr range, we add one note of encouragement: it is quite possible to obtain significant, perhaps even more meaningful results, by looking at the human tooth enamel values in the absence of any estimate of a local range at all. As Bentley et al. [4] have reported, for example, the mean tooth enamel 87Sr/86Sr value at Dillingen is 0.709590.00097 for females and 0.708970.00052 for males, a difference which is 95%

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sure to be significant (one-tailed t-test). Perhaps even more important is the fact that the variance in the 87 Sr/86Sr values is higher for females, also 95% significant (F-test). A higher variance indicates that females were more often the non-locals than males. Similarly for Vaihingen, we can make a meaningful interpretation without defining the local range, as the variance in human enamel 87Sr/86Sr values from the ditch burials is significantly larger than those from the settlement (F-test P=0.04). Correlations between 87Sr/86Sr and artifacts can also present meaningful patterns whether or not a local range is defined. At both Dillingen and Flomborn the mean 87 Sr/86Sr value for individuals buried with a polished stone adze (‘shoe-last adze’) is lower than for those without one, a difference which is 87% significant at Dillingen and 94% significant at Flomborn (one-tailed t-tests). Because we know generally what the 87Sr/86Sr range is at each site, we can make the rather exciting conclusion that females and people buried without adzes were more likely to be non-locals at Dillingen and Flomborn [4]. Importantly, we make this conclusion with statistics and confidence in the chemical integrity of human tooth enamel, and without undue reliance on an over-precise definition of a local range.

Acknowledgements We thank Priv.-Doz. Dr Ru¨diger Krause (Landesdenkmalamt Baden-Wu¨rttemberg) for providing the samples from Vaihingen, for helpful comments on this manuscript, and for his ongoing assistance in this project. We also thank Dr Rex Taylor, Tina Hayes and Dr Matthew Cooper of the School of Ocean and Earth Science, Southampton Oceanography Centre, where the TIMS analyses were performed for this study. James Burton, as always, has been a source of inspiration and assistance.

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