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1.
The use of stable carbon isotopic analysis of bone apatite to reconstruct prehistoric diets is hindered by the possibility of diagenetic alteration of carbonate during burial. We examine apatite preservation in Classic Period Maya skeletal remains from Dos Pilas, Guatemala, using Fourier transform infrared spectroscopy (FTIR). We use weight % CO2evolved from apatite, FTIR carbonate/phosphate absorbance ratios, phosphate peak splitting crystallinity indices, fluoride peaks, and stable oxygen isotopic ratios to identify diagenetic change in apatite chemistry. Isotopically light carbon taken up from burial soil is adequately removed from most Dos Pilas bone by treatment with dilute acetic acid, but more severe alteration cannot be reversed by standard preparation methods. Infrared criteria identify recrystallized apatite in a subset of Dos Pilas burials, that is accompanied by isotopic exchange, and that no longer preserves biogenic δ13C. These results illustrate that comparatively recent bone may be diagenetically altered and demonstrate a need for systematic evaluation of mineral integrity in all archaeological bone prior to interpreting paleodiets with apatite δ13C.  相似文献   

2.
This study applies an intra-skeletal sampling strategy to examine post-mortem alteration of archaeological human bone from west Mexico, and to reconstruct ancient diet. Human bone from the Chupicuaro culture (Mexico, Preclassic period) constitutes an ideal material with which to examine subsistence strategies because the specific hydrothermal environment in which the population lived would have provided certain food components (hydrothermal waters and carbonates) with distinct signature in Ca, Mg, F, Li, Sr, Mn, V and U values. Four to ten samples were taken from the long bones of six skeletons. Bone trace element content (Ca, P, F, Mn, Mg, Na, Li, V, Zn, Rb, Sr, Ba, Y, La, Ce, Nd, Th, U) and bone alteration parameters (crystallinity, organic matter and secondary calcite content) were analysed at the intra-skeletal level. Stable isotopic signatures (bone δ13C and δ18Ocarbonate) and histological analyses were also performed on a single bone from each individual. Results indicate that all of the skeletons were affected by post-mortem mineralogical, structural and geochemical transformations. Biological bone δ13C values seem preserved for most of the individuals but an increase in crystallinity accompanies depletion in bone δ18O values. The combination of bone alteration parameters with bone elemental content shows that in this very specific context, a widespread dissolution-recrystallisation is unlikely. Of the hydrothermal tracers, Sr, F and Li were of particular interest because their retention in living tissues is related to the amount ingested. The intra-skeletal Li content does not reveal any pattern but Li depletion is not excluded. In contrast, Sr and F show a progressive intra-skeletal diagenetic enrichment likely due to gradual diffusion–adsorption processes. The bones with the lowest concentrations in these elements are assumed to yield the best representative ante-mortem values. The signal extracted from each skeleton, a very unusually high bone Sr, F and Li content, is interpreted as reflecting the consumption of the local hydrothermal products, which are also enriched in these elements.  相似文献   

3.
The calcium isotope ratios (δ44/42Ca) of bones from humans and fauna from three archaeological sites, Taforalt, Abu Hureyra, and Danebury, are evaluated in order to assess whether calcium isotope ratios of bones can be used to detect dairy consumption by adult humans. At each site the fauna δ44/42Ca is the same regardless of species, while the humans have lower δ44/42Ca than the local animals by 0.24–0.41‰ (site means). However we cannot ascribe this difference to dairy consumption, given this human–faunal difference also occurs in Epipalaeolithic and Mesolithic adult humans, where dairy consumption is unlikely. Rather, this difference appears to be a result of differences in metabolic processes or other aspects of diet between humans and fauna. Minimal isotopic change in sequential acid leaches of bone powders and consideration of the high calcium concentration in bone suggest that bone calcium isotope ratios are not substantially affected by diagenetic change.  相似文献   

4.
In this paper, we investigate the potential use of oxygen and strontium isotope ratios (δ18Op and 87Sr/86Sr) measured in archaeological fish enamel as provenance indicators. δ18Op and 87Sr/86Sr were measured in a suite of archaeological carp remains recovered from the Anatolian townsite of Sagalassos dated to the Early Byzantine period (AD 450–650) and compared to that of modern fish, river and lake waters from the Anatolian region. We used sequential leaches in weak acetic acid to remove diagenetic Sr from fossil tooth enamel, monitoring the effectiveness of this approach by measuring the Sr/Ca ratios of the leachates via an isotope dilution thermal ionization mass spectrometry method (ID-TIMS). δ18Op values mostly excluded a riverine origin. 87Sr/86Sr ratios of one fish overlapped with the 87Sr/86Sr signatures of two lakes in the Anatolian region, and at least one lake (Gölcük) could be removed as a candidate owing to a very distinctive 87Sr/86Sr signature not found in any of the fish remains. Most of the tooth samples analyzed could not be assigned a precise geographical origin since the 87Sr/86Sr ratios measured in enamel did not match that of any of the local lakes selected as potential origin. This result suggests that carp may have originated from lakes that have not yet been sampled, although this conclusion is not supported by other archaeological evidence. Alternatively, the lack of correspondence between lakes and fish Sr isotope ratios highlights several possible sources of uncertainties including spatial heterogeneity in 87Sr/86Sr ratio within a lake, the contribution of dietary strontium to the 87Sr/86Sr ratio of fish tooth enamel, and post-mortem alteration of the tooth Sr isotope signal during fossilization. In spite of the high precision of the strontium isotope analyses and the wide range of variation in the surface waters of the Anatolian lakes and rivers, this method may remain limited to distinguishing between lakes situated in regions of bedrock of very distinct age and geology until these sources of uncertainty are more fully investigated.  相似文献   

5.
Ritual tooth ablation was extensively practiced among Jomon (Japanese Neolithic) societies in their final phase (ca. 3000-2300 BP). This tradition includes two different tooth ablation patterns, type 4I and type 2C, referring to extraction of the mandibular incisors and canines, respectively. However, the reason for this difference is unclear. Previous carbon and nitrogen stable isotope analysis of human remains from the Inariyama shell mound revealed that type 4I individuals were more dependent on terrestrial resources and type 2C individuals on marine resources. To test this hypothesis, we performed strontium (Sr) isotope (87Sr/86Sr) analyses on the same skeletal remains and on modern plants around the site. Because Sr isotope ratios of plants differ according to the local geology and seawater has a consistent Sr isotope ratio, the Sr isotope ratios of tooth enamel can reveal both migration and diet. Comparing Sr isotope ratios in plants and seawater with those of tooth enamel, we identified four possible immigrants. Type 4I locals had significantly higher Sr isotope ratios than type 2C locals. The ratios of the type 4I and type 2C locals were close to those of terrestrial plants and seawater, respectively, suggesting that type 4I locals had incorporated much Sr from terrestrial resources and type 2C locals from marine resources. These results support the hypothesis that ritual tooth ablation reflects dietary differences throughout an individual’s life, and they suggest possible occupational differentiation among the Jomon people.  相似文献   

6.
We have explored laser depth profiling to obtain data sets for U-series as well as Sr analyses. Laser probing with an 81 μm spot size allows for the exploration of low uranium domains of up to 400 μm below the outer surface in tooth enamel. These low U domains will contain Sr isotope compositions of the individual, that are least affected by diagenetic Sr overprints. The small holes drilled for U surveying are not visible to the naked eye. Using larger spot sizes of around 233 μm, laser drilling can be used to obtain reliable U-series isotope data to a depth of approximately 1000 μm in enamel and around 1300 μm in bone. Furthermore, meaningful 87Sr/86Sr isotope data can also be obtained with this spot size. Using our sampling strategy, the overall damage to a human tooth is minute, as demonstrated on a Neanderthal tooth from Moula-Guercy. We expect that laser ablation depth profiling will become routine for gaining insights into the age of human fossils and the migrations of ancient humans.  相似文献   

7.
This study tests the precision and accuracy of laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) for measuring strontium isotope ratios (87Sr/86Sr) in fossil teeth from Swartkrans and Sterkfontein in South Africa, and explores the extent of diagenesis in these specimens. Compared to solution MC-ICP-MS or thermal ionization mass spectrometry (TIMS) methods, LA-MC-ICP-MS can be faster and less expensive, but has lower precision and accuracy. We found that 87Sr/86Sr ratios in fossil rodent teeth measured by LA-MC-ICP-MS were offset from solution values by a mean of 0.0005 ± 0.0010 (2σ). Because of the very wide spread of biologically available 87Sr/86Sr ratios (∼0.710 to ∼0.790) in the region, LA-MC-ICP-MS is more than sufficient for assessing the geographic origins of the fossil rodents. The concentration of strontium in modern and fossil enamel from the area is statistically indistinguishable, as is the range of 87Sr/86Sr ratios in modern rodents and fossil rodents from Swartkrans. Thus, there is little evidence of diagenetic Sr in the fossil enamel. In contrast, the fossil dentine may contain up to ∼50% diagenetic strontium, although many dentine 87Sr/86Sr ratios are still far removed from the background cave value of 0.729. We propose that LA-MC-ICP-MS will also be of use for investigating the geographic origins of other, non-rodent fossil teeth from the Sterkfontein and Swartkrans collections, and may prove of similar utility at other suitable sites.  相似文献   

8.
Distinct patterns can be discerned in the extensive ritual tooth ablation found among the human skeletal remains of the Late–Final Jomon period (ca. 3200–2800 cal BP) in Japan. Based on comparative observations of sex and grave patterns in the skeletal remains, two major patterns in ritual tooth ablation, termed type 4I and type 2C, have been assigned to locals and immigrants, respectively. In order to test this hypothesis, strontium (Sr) isotope (87Sr/86Sr) analyses were performed on human skeletal remains from the Yoshigo shell mound in Aichi Prefecture, central Japan. Plants in the surrounding area were also examined to illustrate the geographic 87Sr/86Sr distribution. The Sr isotopic variation in human tooth enamel (87Sr/86Sr = 0.70868–0.71028) was greater than that in human bones (87Sr/86Sr = 0.70871–0.70943). Individuals with higher Sr isotope ratios in their tooth enamel than seawater Sr values of 0.7092 can be identified as immigrants (36% of population). The presence of these isotopically identified immigrants between both type 2C and type 4I individuals does not support the previous hypothesis. The intra-population 87Sr/86Sr distribution of tooth enamel of type 2C individuals showed a significantly higher mean ratio than that of type 4I individuals, suggesting a higher proportion of immigrants among the former.  相似文献   

9.
As evidence concerning human mobility during the transition to agriculture in central Europe, we present the results of strontium isotope analysis of human skeletons from the Neolithic village of Vaihingen, Germany. We find significantly more ‘non‐local’87Sr/86Sr values from humans buried in a Neolithic ditch surrounding Vaihingen than from those buried within the settlement. These results fit with previous studies showing a correlation between burial circumstances and strontium isotope signatures from LBK cemeteries of southwestern Germany ( Price et al. 2001 ; Bentley et al. 2002 ). A pilot study of Neolithic animal teeth from Vaihingen suggests that either ‘local’87Sr/86Sr signatures were more variable than the analysed human bones suggest, or that these domestic animals themselves were mobile, perhaps ranged by mobile pastoralists.  相似文献   

10.
The site of Conchopata in the central Peruvian Andes was the secondary center in the heartland of the Wari Empire (AD 600–1000), and in this study we examine whether this urban locale was populated by locals, voluntary migrants from distant regions, and/or captives who were forcibly brought to Conchopata. We examine radiogenic strontium isotope ratios from 72 dental enamel and bone samples representing 31 formal burials and 18 human trophy heads to distinguish between locals and non-locals, and we examine skeletal and archaeological data to establish whether non-local persons were voluntary migrants or captives. We also describe a new, straightforward technique in the evaluation of radiogenic strontium isotope ratios to assist in detecting non-locals when large datasets are available.Results show that natal Conchopata inhabitants should exhibit radiogenic strontium isotope ratios that range from 87Sr/86Sr = 0.70548 to 87Sr/86Sr = 0.70610. Thus, among the 31 burials, 29 exhibit local values, suggesting that Conchopata was not a cosmopolitan center to which numerous foreigners migrated; rather, it was populated by local peoples, likely the descendants of the preceding Huarpa culture. The two individuals with non-local radiogenic strontium isotope ratios are an infant and a 17–22 years old female. The archaeological context suggests that the female may have been taken captive for subsequent sacrifice, as she was interred in front of the ritual D-shaped structure in which decapitated human heads (trophy heads) and sacrificed camelids were deposited. Among the 18 trophy heads sampled, 14 have non-local values, confirming previous studies of smaller samples that suggested that Wari warriors travelled to other locales and took captives—both adults and children—for subsequent transformation into trophy heads. Additional analyses of bone-tooth pairs from a subsample (12 burials and six trophy heads) shows that the burial group was much more sedentary (homogenous radiogenic strontium isotope ratios in bones and teeth) and the trophy head individuals were much more mobile (heterogenous radiogenic strontium isotope ratios in bones and teeth). Overall, the multiple lines of evidence support the notion that the Wari Empire occasionally used militaristic means, combined with elaborate ritualism, to subjugate other populations, a tactic that may have helped Wari establish and maintain control in particular regions in the Andes.  相似文献   

11.
Changes in the stable carbon and nitrogen isotope ratios of modern bone samples heated to a variety of times and temperatures were used to determine the effect of heating on isotope ratios and the retention of organic matter in charred bones. For organic extracts produced by slow demineralization in weak acid, δ13C values were unchanged, while δ15N values increased by up to 5‰ and were primarily determined by heating temperature. Changes in the electron spin resonance (ESR) g-value of whole bone and organic extracts were also measured. For organic extracts from charred bones, the g-value was well-correlated with δ15N and temperature, suggesting that g-values could be used to estimate the charring temperature and original δ15N values of charred bones. Thus, g-values from demineralized extracts could be very useful in forensic investigations where it would important to reconstruct the thermal history of burned bones. Isotope ratios and g-values of demineralized extracts from four prehistoric components at three sites that produced cremated human bone were used to test whether the same approach can be applied to archaeological materials. While carbon isotope ratios of the prehistoric samples were similar to those of uncharred specimens, nitrogen isotope ratios were increased and the g-value corrections for nitrogen isotope ratios were not effective.  相似文献   

12.
Archaeologists have generally avoided analyzing inorganic isotopes in bone because of its high porosity, large crystalline lattice spacing, and small crystallite size, making it particularly susceptible to diagenetic alteration. Because the inorganic isotopes are left unstudied, we lose a significant portion of information pertaining to an individual’s life history, such as migration, health, and ranging behavior. Tooth enamel, which does not have the same susceptibility to diagenesis as bone, can be used to extract this information but this means that taxa lacking teeth, such as birds, some species of fish, and some reptiles, are excluded. Here, we present a method that can be used to identify diagenetic alternation in bone. This is done by focusing on abnormal concentrations of vanadium and uranium. Neither element is readily bio-precipitated into hydroxyapatite due to ionic radius, vibrational frequency, atomic mass, and ionic charge. This makes them an ideal marker for diagenetically altered bone. Vanadium occurs in very low concentrations in modern bone, while archaeological bone shows clear evidence of normal, non-diagenetically altered values alongside high concentrations of vanadium in diagenetically altered bone. Uranium also is a measure of diagenetic alteration, as modern bone has concentrations below detectable limits (0.017 ppb), while some archaeological bone contains uranium above detectable limits. The biogeochemistry of these elements in soil and bone are discussed with implications for enamel studies.  相似文献   

13.
Multi-isotope fingerprints in the bioapatite of archaeological skeletons are mostly superior over single isotope analyses for provenance studies. Gaussian mixture model (GMM) clustering is a novel tool for a similarity search among multidimensional data sets and at the same time permits the evaluation of the structural importance of particular isotopic ratios in the data set. We applied three GMM clustering experiments on multi-isotope fingerprints—stable strontium (Sr), lead (Pb) and oxygen (O) isotopic ratios—established in 217 archaeological animal bones excavated along a specific transect across the European Alps. This reference region had been in use since prehistoric times by humans who crossed the Alps from north to south, and vice versa. The resulting clusters permit a spatial assignment of the specimens with a very high probability, in particular with regard to the geological complexity of the region. A combination of Sr with Pb stable isotopes led to an optimal differentiation between the southern and northern Alpine forelands that cannot be distinguished from each other by 87Sr/86Sr ratios alone, while the contribution of δ18O is not particularly high. The isotopic mapping and subsequent cluster analysis is suitable for the analysis of archaeological human finds and the reconstruction of the direction of transalpine mobility and trade.  相似文献   

14.
The value of strontium isotope analysis in identifying immigrants at numerous archaeological sites and regional areas has been demonstrated by several researchers, usually by comparing 87Sr/86Sr values of human tooth enamel and/or bone with the local strontium isotope signature determined by faunal and environmental samples. This paper examines the feasibility of using 87Sr/86Sr ratios to investigate residential mobility in the Nile Valley region, specifically at the New Kingdom period (∼1050–1400 BC) archaeological site of Tombos (ancient Nubia). Archaeological and textual information regarding this period indicates that immigrant Egyptians and local native Nubians were likely interacting at this site during a period of Egyptian colonial occupation. The results of this study suggest that non-local individuals may be distinguished from locals using 87Sr/86Sr values and that colonial agents in the Tombos population were probably both local native Nubians and immigrants.  相似文献   

15.
Spacing between stable isotope values in bones and teeth is a valuable tool for examining dietary influences and diagenesis. This study examines carbon and oxygen isotope values from collagen and hydroxyapatite (structural carbonate and phosphate) in archaeological human bones and teeth to derive species‐specific correlation equations and isotope spacing values. The δ13Ccollagen and δ13Cstructural carbonate in bone and dentin collagen show a strong correlation (R = 0.87, 0.90, respectively) with an average Δ13Ccarb‐coll spacing of 5.4‰. The consistency of this isotope spacing with other large mammals and in humans with both low and high protein intake (as indicated by enriched δ15N values) suggests a similar allocation of protein‐derived carbon and whole diet‐derived carbon to collagen and structural carbonates, respectively, as other terrestrial mammals regardless of absolute meat intake. The δ18Ostructural carbonate and δ18Ophosphate show the strongest correlation in enamel (R = 0.65), weaker correlations in dentin (R = 0.59) and bone (R = 0.35), with an average Δ18Ocarb‐phos of 7.8‰. This isotope spacing is slightly lower than previously reported for large mammals and limited available data for humans. The results potentially indicate species‐specific fractionations and differing access to body water and blood‐dissolved inorganic carbonates in the presence of collagen formation. The use of correlation between δ18Ostructural carbonate and δ18Ophosphate to determine diagenetic state is not recommended. The strength of this correlation observed in bones and teeth is variable and alternate indicators of diagenetic state (i.e. C:N ratios of collagen) provide more robust and independent evidence of isotope preservation despite presence/absence of a strong isotope correlation. Published 2012. This article is a U.S. Government work and is in the public domain in the USA.  相似文献   

16.
The principles behind the strontium isotopic system are an important tool for archaeologists tracing human migration and patterns of movement in prehistory. However, there are several scientific challenges of analytical nature, as well as those which relate to unknown parameters inherent to the interpretation of such data. One prerequisite is the knowledge of the range of strontium isotopic ratios that best characterize the bioavailable fractions of a particular area of interest. The study reported here attempts to establish a baseline for strontium isotope signatures valuable for Denmark (excluding the island of Bornholm) and particularly for the use in archaeological investigations. We present strontium isotope ratios of bones and teeth from modern mice contained in owl pellets, of snail shells, and of archaeological fauna samples. We compare these ratios with median strontium isotope signatures characterizing human enamel populations from archaeological sites within Denmark. The fauna samples reported here range from 87Sr/86Sr = 0.70717 to 0.71185 with an average of 0.70919, and human enamel defines a range from 87Sr/86Sr = 0.7086 to 0.7110 with an average of 0.7098. In both datasets, we observe a small difference between the baseline values for the western (Jutland) and eastern (Funen, Zealand, and the southern islands) parts of Denmark. We therefore propose two slightly different baseline ranges with a partial overlap for the isotopic signatures of bioavailable strontium fractions within Denmark, namely a range of 87Sr/86Sr = 0.7078–0.7098 for the western area and a range of 87Sr/86Sr = 0.7089–0.7108 for the eastern parts.  相似文献   

17.
A collection of 31 glass fragments, dated to the 3rd to 7th century AD and excavated in Veh Ardašīr, (modern Iraq), were analysed for their Sr and Nd isotopic compositions with the aim of deepening our knowledge on glass circulating within central Mesopotamia during Sasanian times and to highlight the merits of isotope ratios for the definition of the production scenery. Based on the elemental composition of the samples, two groups related to the exploitation of different plant ashes were previously distinguished, and also a change in the silica source in the course of the 4th century AD emerged. The determination of isotopic distributions of Sr and Nd offers a deeper insight. The 87Sr/86Sr isotope ratio, together with the Sr elemental concentration, confirms this use of different plant ashes, and permits one to distinguish distinct glass batches, although the isotopic Sr signature does not allow us to highlight evidences of different provenances for the samples of different composition. Moreover, the 143Nd/144Nd isotope ratio suggests the use of sands belonging to a common geological area, and also allows the identification of a set of samples that were possibly produced exploiting a further different sand source. As a whole, Sr and Nd isotope ratio values for the samples considered, i.e. 87Sr/86Sr = 0.70833 to 0.70916 and ?Nd = −8.69 to −4.98, differ from the published isotopic data on middle Eastern glass samples and can therefore define a characteristic Sr–Nd signature for plant-ash Sasanian glass excavated in Veh Ardašīr.  相似文献   

18.
This study explores the feasibility of using strontium isotope (87Sr/86Sr) analyses of enamel from domestic dogs (Canis familiaris) to investigate networks of exchange in the prehistoric Circum‐Caribbean. Dog teeth were obtained from burial and domestic contexts from two prehistoric sites (Anse à la Gourde and Morel) on Grande‐Terre, Guadeloupe (Lesser Antilles). Strontium isotope results were compared with local biosphere 87Sr/86Sr data at the scale of the site, island and archipelago. The isotope results indicate both local and nonlocal origins with three dogs (30%) identified as nonlocal (one from Anse à la Gourde and two from Morel). The variance in 87Sr/86Sr ratios of the nonlocal dog teeth is consistent with diverse multiple origins external to the island of Grande‐Terre but consistent with origins from other islands of the Lesser Antilles. The diverse origins of the nonlocal dog samples indicate that the prehistoric circulation of dogs occurred at multiple scales from regional to long distance. Significantly, the 87Sr/86Sr ratios of some of the dog teeth are comparable with values of nonlocal humans at Anse à la Gourde determined in previous studies. It is possible that these comparable 87Sr/86Sr ratios result from similar natal origins, for example if individuals were migrating to Guadeloupe with dogs. The results of this study contribute to an ongoing regional investigation of the economic, social and political roles of animals and animal remains and the multiscalar networks of prehistoric mobility and exchange in the Circum‐Caribbean region. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

19.
Human skeletal remains from the Neolithic sites BHS18 in the interior of the Sharjah Emirate and the Neolithic shell midden UAQ2 (Umm al‐Quwain) on the coast of the Persian Gulf (United Arab Emirates, UAE) were analysed for their isotope ratios of strontium (87Sr/86Sr) and oxygen (18O/16O). The results are not in agreement with earlier assumptions about a Neolithic nomadism between inland regions and the south‐eastern coast of the Persian Gulf. Existing evidence of nomadic movements of the people from BHS18 most possibly refers to transhumance within the mountains in the hinterland. The strontium isotope measurements on human skeletons from UAQ2 on the contrary indicate uninterrupted residence of this population on the coast. Nevertheless, evidence was found of individual mobility between inland regions and the coast.  相似文献   

20.
The strontium isotope ratio (87Sr/86Sr) is used in archaeological studies to identify major events of population movement in prehistory such as migration, conquest, and inter-marriage. This study shows that the strontium isotope method can be expanded to identify more subtle shifts in prehistoric human mobility. 87Sr/86Sr isotope ratios were analyzed in dental enamel from human and faunal specimens from the Late Neolithic and Copper Age on the Great Hungarian Plain. The archaeological record indicates that several aspects of life changed during the transition from the Late Neolithic to the Copper Age (ca. 4500 BC) in Hungary; evidence for increased interaction over a wide geographical area, less resource pooling and the use of secondary products has been used to support the idea that local populations became more mobile, perhaps due to the adoption of an agro-pastoral economy. Results from this study identify a change in the range of strontium isotope values from the Late Neolithic to the Copper Age from a very narrow range of values to a much broader range of values, which suggests that changes in how land and resources were utilized on the Great Hungarian Plain affected incorporation of strontium into the skeletal system. This study indicates that the strontium isotope ratio is a valuable tool for identifying more subtle changes in prehistoric behavior such as a shift to a more pastoral economy.  相似文献   

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