prehistoric migration at nebira, south coast of papua new guinea: new insights into interaction...

Journal of Anthropological Archaeology 30 (2011) 344–358

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Journal of Anthropological Archaeology

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Prehistoric migration at Nebira, South Coast of Papua New Guinea: Newinsights into interaction using isotope and trace element concentration analyses

Ben Shaw a,⇑, Hallie Buckley a, Glenn Summerhayes b, Claudine Stirling c,d, Malcolm Reid c,d

a Department of Anatomy and Structural Biology, University of Otago, PO Box 913, Dunedin 9054, New Zealandb Department of Anthropology, Gender and Sociology, University of Otago, PO Box 56, Dunedin 9054, New Zealandc Department of Chemistry, University of Otago, PO Box 56, Dunedin 9054, New Zealandd Centre for Trace Element Analysis, University of Otago, PO Box 56, Dunedin 9054, New Zealand

a r t i c l e i n f o a b s t r a c t

Article history:Received 14 July 2010Revision received 20 May 2011Available online 12 June 2011

Keywords:StrontiumOxygenBariumMobilityAustronesiaBioarchaeology

0278-4165/$ - see front matter � 2011 Elsevier Inc. Adoi:10.1016/j.jaa.2011.05.004

⇑ Corresponding author.E-mail address: [email protected] (B

Migration is a commonly used explanation for cultural change in world prehistory, and is also a centraltheme in the prehistory of the Pacific Islands. However it is rarely subject to direct archaeologicalresearch. This paper applies strontium and oxygen radiogenic/stable isotope (87Sr/86Sr, d18O), and traceelement concentration (Ba/Sr) analyses to 27 individuals buried at the archaeological site of Nebira(ca.720–300 BP), located inland on the South Coast of Papua New Guinea. The analyses seek to identifynon-local individuals within the population and provide a more in-depth understanding about the socialidentity of the possible migrants in this community.

The strontium isotope data indicates that five individuals were non-local to Nebira, having possiblycome from a coastal location. Correlation with biological data, such as age and sex, also indicates thatthe pattern of migration at Nebira was not sex or age specific. The results support the archaeological find-ings that suggest the inhabitants from Nebira were in contact with coastal communities during a periodin prehistory of increased cultural interaction. However, despite the considerable isotopic variation iden-tified in the Nebira sample, it is also demonstrated that more research is needed to identify the possibleorigins of these non-local individuals.

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Introduction

The migration and mobility of people in prehistory influencedboth the cultural development and biology within and betweencommunities (Adams et al., 1978; Anthony, 1990; Shaw, 1975). Re-cently, studies of migration using radiogenic and stable isotopes, aswell as trace element concentration analyses, have proven verypowerful in Europe and the Americas for understanding the move-ment of people during crucial periods of change in prehistory(Bentley et al., 2002; Evans et al., 2006b; Knudson and Price,2007; Montgomery et al., 2005; Price et al., 2004; Slovak et al.,2009; Turner et al., 2009). The incorporation of these isotope andtrace element concentration analyses into broader archaeologicalresearch programmes to investigate prehistoric migration hasgained momentum in recent years (Bentley et al., 2007a,b). Thishas been facilitated by improvements in analytical and interpretivetechniques, primarily by increasing instrument sensitivity used tomeasure isotopic composition. Advances in the methods of defin-ing local population isotopic variation and the increasing abilityto detect and control diagenetic contamination in skeletal and den-

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. Shaw).

tal tissues have also contributed to the improvements of the anal-yses (Bentley et al., 2004; Price et al., 2002).

These studies have provided more subtle details about the rela-tionships and interactions between local and migrant individualsin a prehistoric population. This has primarily been achieved byidentifying variations in the chemical signatures from skeletaland dental tissue to determine non-local influences in a skeletalassemblage (Bentley et al., 2003, 2008; Knudson, 2008, 2009; Priceet al., 2006b, 2004; Tafuri et al., 2006). Biocultural informationsuch as age, sex, burial position and the distribution of burial goodsin a cemetery may also offer detailed insights into the social struc-ture of a prehistoric community. Biocultural information may alsobe used to help determine whether identified non-local individualswere treated differently to the local population (Knudson andStojanowski, 2008; Knudson et al., 2004). Social phenomenon suchas marriage patterns (Bentley et al., 2005), warfare (Knudson et al.,2009), kinship (Bentley et al., 2008; Tafuri et al., 2006) and culturecontact (Bentley et al., 2003; Price et al., 2006b) have also beenassessed using this approach.

The diversity of culture and human biology in the Pacific Islandsprovides a useful and unique context for assessing the influence ofmigration on prehistoric cultural development, trade systems andchanges in interaction patterns, both spatially and temporally.

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Migration and trade interactions were evidently necessary for sur-vival in this complex and often isolated island environment(Anderson, 2001; Summerhayes, 2007). Over the past 50 years orso, archaeological and anthropological research in the Pacific hasprovided a solid foundation for understanding prehistoric tradeand interaction across a wide range of cultural and environmentalsettings. This has been achieved through the study of material cul-ture (Allen, 1977a, 2000; Ambrose and Green, 1972; Best, 1987;Green and Kirch, 1997; Kirch, 1990; Summerhayes, 2000), linguis-tics (Pawley, 2007; Pawley and Green, 1974) and DNA analyses(Allen et al., 2001; Friedlander et al., 2005; Larson et al., 2007;Matisoo-Smith, 2007; Matisoo-Smith and Robins, 2004). Com-bined, these techniques can provide a wealth of evidence for pre-historic interaction on a regional and population level. However,the application of radiogenic and stable isotope analyses to prehis-toric human remains has the resolution to identify individualnon-locals within a skeletal sample and the potential to assessthe impact of movement and interaction on the population.

Recent research using radiogenic/stable isotope and trace ele-ment concentration analyses to investigate migration patterns ofprehistoric populations in Vanuatu (Bentley et al., 2007b) and theBismarck Archipelago, northeast of Papua New Guinea (Shawet al., 2009, 2010) has provided new insights into questions of col-onization and trade relations during the Lapita period of Pacific Is-land prehistory (Table 1). At the Lapita-associated cemetery site ofTeouma in Vanuatu, the isotopic and trace element evidencesuggested there was a difference in burial treatment between theidentified local and non-local individuals. Four non-local

Table 1Comparative radiogenic/stable isotope data (human and pig) from other sites in the Paciindividual measured values are: 87Sr/86Sr = 0.000014 (±2 SE), d18O = 0.1 (±1 SE) and Log(Ba

Site (date) Island group/province Reference

Teouma (3100–2900 BP) Vanuatu Bentley et al. (2007b)Watom (2750–2400 BP) New Britain Shaw et al. (2010)Anir islands (3200–2700 BP) New Ireland Shaw et al. (2009)Lifafaesing (2500–1020 BP) New Ireland Shaw et al. (2010)

Fig. 1. The South Coast of Papua New Guinea showing location of Nebira. Adapted from Breader is referred to the web version of this article.)

immigrants were identified at Teouma who may represent someof the first colonists to arrive in the archipelago (Bentley et al.,2007b). In the Bismarck Archipelago, isotopic evidence from the la-ter Lapita burial site (Reber-Rakival) on Watom Island suggeststhat these communities were more mobile during this period inprehistory than previously suggested by the archaeological record.Strontium isotopes measured in the teeth of Lapita-associated pigs(an important ritual and trade item in ethnographic and modernMelanesian societies) were identified as coming to Watom fromseveral potentially different local and perhaps distant origins.The movement of pigs in this population suggests that they werean important trade item during this period of prehistory as well(Shaw et al., 2010).

This paper applies radiogenic and stable isotope (87Sr/86Sr, d18O)analyses and trace element concentration (Ba/Sr) analysis to dentaltissue from human skeletal remains interred at the archaeologicalsite of Nebira (ca. 720–300 BP), located inland on the South Coastof Papua New Guinea, from herein referred to as the South Coast(Fig. 1). The purpose of the analysis is to isotopically characterisethe Nebira population and identify any ‘non-local’ individuals in-terred at the site. In this context non-local refers to an individualthat has an isotopic signature that is different from the individualsthat are considered to represent the local population. The mostparsimonious explanation for the difference in the isotopic signa-ture is that the individual migrated, or immigrated, from elsewhereand assimilated into the community prior to their death. Isotopebased methods of identifying migration have not been used inmainland Papua New Guinea before. This is largely because the

fic Islands. Mean values for pig samples are in brackets. Typical analytical errors for/Sr) = 0.0004 (±1 SE). In all samples, oxygen isotope standard used was V-SMOW.

Samples Isotope and trace element mean values

Human Pig 87Sr/86Sr d18O Log(Ba/Sr)

17 0 0.70776 24.7 �1.8815 6 0.70768 (0.70795) 23.9 (24) �1.73 (�1.39)

5 5 0.70673 (0.7066) – –5 0 0.70899 24.5 �1.69

ulmer (1978). (For interpretation of the references to colour in this figure legend, the

346 B. Shaw et al. / Journal of Anthropological Archaeology 30 (2011) 344–358

geochemistry is not well understood in terms of characterising re-gional isotopic variation, but also the number of archaeologicalskeletal assemblages is limited. Therefore issues surrounding theestimation of local isotopic variation within a sampled populationwill need to be addressed. Nonetheless, if non-local individuals areable to be identified at Nebira it will add further insight into pos-sible interaction with other communities in the region.

Shellfish refuse in archaeological deposits at Nebira indicatethat the people living there were in contact with at least somecommunities on the coast. The inland location of Nebira, and thepresence of these coastal resources, led Allen (1972: p. 122) toput forth the ‘outstation’ hypothesis which argues that Nebiraserved as a hub of reciprocal trade between coastal and inlandcommunities, exchanging coastal resources (shellfish, fish) for in-land resources (presumably vegetables and animals). Although thishypothesis was developed based on the earlier occupation of thesite, the presence of shellfish (albeit smaller quantities) in the lay-ers contemporary with, and immediately above the burials sug-gests the basic premise of this hypothesis can also be applied tothe later occupation at Nebira as well. Several of the shellfish spe-cies were also used as artefacts associated with the burials. Thispaper will therefore also investigate whether people were them-selves moving, as well as the material culture previously identifiedin the archaeological record (Bulmer, 1978). The correlation of theisotope and trace element concentration data with biological (age,sex and trauma) and archaeological (burial context) informationwill also be investigated to address the social context for migrationat the Nebira site.

Archaeology of the South Coast – a brief background

The chronology of human occupation in New Guinea (NorthernSahul) extends back some 50,000 years with the introduction of anapparent mobile hunter/gatherer society (Fairbairn et al., 2006;Summerhayes et al., 2010; O’Connell and Allen, 2004; O’Connorand Chappell, 2003). However, despite the long chronology ofoccupation in New Guinea, archaeological research on the SouthCoast indicates that intensive occupation did not occur until ca.2000 BP (Allen et al., 2011), or perhaps slightly earlier (Bulmer,1999; McNiven et al., 2006; Negishi and Ono, 2009), with the wide-spread introduction of a ceramic manufacturing (Early Papuan Pot-tery) group of people (Summerhayes and Allen, 2007) (Table 2).

Beginning around 1200 BP along the South Coast, there was awidespread and rapid change in settlement patterns and ceramicdesign, termed by some as the ‘ceramic hiccup’, whereby a second-ary migration of people were thought to have come from theislands to the east in the Milne Bay province (Allen, 1977a; Irwin,1985; Rhoads, 1982) (Table 2). However, re-analysis of thearchaeological data suggests these changes were more likely tohave occurred as a result of local social re-organisation, rather thanthrough large scale external influence (Irwin, 1991; Summerhayesand Allen, 2007). Nonetheless, it was during and after this period inprehistory when localised and specialised maritime tradenetworks are thought to have developed along the South Coast.This is recognised archaeologically by the increased presence of

Table 2The South Coast prehistoric sequence.

Period Approximate date range

Pre-ceramic ?–2000 BPColonization >2000–1600 BPRegional isolation 1600–1000 BPPottery transformation 1200–800 BPInteraction, specialisation and exchange 800–200 BPBeginning of Hiri trade ca. 500 BP

non-local style pottery at sites in the region (Allen, 1977a). Largescale maritime trade is thought to have begun around 500 BP(16th century AD) with the establishment of the Hiri trade, wherelarge quantities of pottery vessels from along the South Coast weretraded for valuable items and food resources, primarily wood andsago (Metroxylon sagu), with the communities further west in theGulf Province (Allen, 1977b, 1982; Bulmer, 1979; Rhoads, 1982).The Hiri trade persisted until the mid-1900s and has been the sub-ject of many anthropological and archaeological studies (Harding,1994; Oram, 1982; Rhoads, 1982).

Geology of the South Coast

The majority of the South Coast is made up of two geologicalstructural regions – The Aure Trough and the South-east PapuaVolcanic Province (Löffler, 1977). The Aure Trough is some16,000 m deep which has filled up with sediment over geologicaltime and has subsequently undergone multiple uplift events thatmixed many of the underlying sedimentary layers (Bain, 1973).The division between these two regions lies close to the moderncity of Port Moresby, resulting in a highly complex geology of theland surrounding the site of Nebira. The geology can be broadlycategorised as Miocene (ca. 23–5.3 mya) and Pliocene (ca. 5.3–2.6 mya) aged deposits of relatively coarse grained greywackesandstones derived from volcanic rock, basaltic lavas with depositsof siltstone, shale, conglomerate, chert and uplifted limestone out-crops along the coast (Fig. 2).

Previous geochemical research of the volcanic belts in PapuaNew Guinea provide an indirect proxy for the radiogenic strontiumisotopic values that would be expected in the geological environ-ment along the South Coast (Hegner and Smith, 1992; Page andJohnson, 1974; Smith and Compston, 1982). The Southern VolcanicBelt runs intermittently down the Owen Stanley Range and alongthe South Coast near Port Moresby, mixing with various submarinebasalts and sedimentary rock of different geological ages. Stron-tium isotopic ratios obtained from six samples along this volcanicbelt range from 0.70364 to 0.70491 (Hegner and Smith, 1992;Smith and Compston, 1982), which are similar to strontium isoto-pic values obtained from the highland regions and other parts ofeastern Papua New Guinea (Page and Johnson, 1974). However,deposits of marine-derived rock and sediments such as limestonefound along the South Coast typically yields strontium isotope val-ues similar to seawater (ca. 0.7092) (Burke et al., 1982; Veizer,1989).

As a result of this geological mixing, the strontium signature forthe area in the vicinity of Nebira is likely to be similar to, or slightlymore elevated than the values obtained for the Southern VolcanicBelt. Without mapping strontium isotope values directly from theunderlying geology, and perhaps the plants near Nebira it is diffi-cult to assess the level of localised isotopic variation in the area.It may therefore not be possible to ascertain the origins of anynon-local individuals identified in skeletal assemblages from Pa-pua New Guinea without detailed isotopic mapping. Even then thistask may remain impossible to achieve with any certainty giventhe complexity of the regional geology.

The archaeological context of Nebira

Nebira is situated on a steep double peaked hill (180 m high),ca. 11 km inland from the coast near the modern city of PortMoresby (Fig. 1). The majority of sites in the region are locatedon the coast, or are situated on offshore islands close to the coast(Bulmer, 1969, 1978; Summerhayes and Allen, 2007; Vanderwal,1973). The exception to this pattern is the inland site of Nebira(Summerhayes and Allen, 2007). The inland plain where Nebirais situated provided ample food resources with easy access to the

Fig. 2. The generalised geology of Papua New Guinea. The archaeological site of Nebira is located behind the labelled city of Port Moresby. Adapted from Löffler (1977).


fertile land for gardening, a range of animals to hunt including wal-laby (Macropus agilis), pig (Sus scrofa), bandicoot (Peroryctesbroadbenti) and cuscus (Phalanger orientalis), with the nearby Lal-oki River supplying a permanent freshwater source (Bulmer,1978, 1979).

Despite access to inland resources, the presence of coastal re-sources were noted with reasonable quantities of whole shells(>20 hard and soft shore species), fish and turtle bone indicatingthat shellfish and fish were transported to Nebira intact and pro-cessed on-site (Allen, 1972; Bulmer, 1978). Reciprocal trade linksfrom Nebira to coastal sites is more difficult to determine but itis assumed that some animal remains found in coastal sites wouldhave come from inland sources. Nonetheless, interaction withcoastal communities would have involved a relatively lengthy trekacross the inland plains and coastal hill systems, or an even longerboat trip as the river reaches the sea some 32 km to the northwest(Bulmer, 1978).

Excavation on the hill saddle of the Nebira site in 1968–1969 re-vealed evidence of extensive prehistoric occupation, as well as theinhumations of ca. 45 individuals (Bulmer, 1978). A detailed anal-ysis of age, sex and burial position of the individuals from Nebira ispresented in Pietrusewsky (1976). The interment of several indi-viduals in a grave at the same time (simultaneous burial) suggests

these individuals may have been related, possibly reflecting famil-ial relationships (Bulmer, 1978) (see Table 3 and Fig. 3). The closeproximity, or clustering, of other interments to each other (groupburial) may also indicate familial relationships (Bulmer, 1978).However, in many cases this grouping was a result of the bonesbeing pushed to the side when the grave was re-used at a laterdate. These groupings may therefore simply reflect intensive recy-cling of the space used as a burial ground rather than familial rela-tionships (Bulmer, 1978; Pietrusewsky, 1976).

The burials at Nebira have been divided into an early and latephase based on their relative positions in the sub-stratum (Bulmer,1978). Early burials were dug into the sterile sandstone sediment,whereas the late phase burials were cut into the cultural strati-graphic layers above the sterile deposits and are also disturbedby later use of the burial ground as a living area (Fig. 3). A customthat was particularly noted by Bulmer (1978) in the Nebira burialswas the apparent practice of leaving the grave open until decom-position had commenced. This activity was argued by Bulmer(1978) to be reflected in the disarticulation of the mandible fromthe skull and of the phalanges. Indirect evidence is also argued toreflect this practice with probable ‘grave houses’ being built overthe grave, which Bulmer (1978) suggests may have been used toprotect the body from outside taphonomic influences during

Table 3Teeth samples and details of the burials included in the radiogenic/stable isotope and trace element concentration analysis from the Nebira site. Age: Young = 20–29.9, Mid = 30–39.9, Old = 40 + Tooth: Mand. = Mandible, Max. = Maxilla, M1 = First molar. Burial type: Single = individual buried by themselves, Sim. (Simultaneous) = individuals buriedtogether. Group = a cluster of individuals buried separately but close together that may be associated with each other. Numbers in parentheses indicate which individuals (burialnumber) are associated with each sampled individual. Bolded numbers within parentheses indicate the individual was sampled for analysis. Age and sex data from Pietrusewsky(1976). Trauma data from Scott and Buckley (2010).

Burial Period Age Sex Burial treatment Burial goods Cranial trauma Tooth sampled

1 Late Young Male Single Yes No R mand. M12 Late Mid Male Single Yes Yes L max. M13 Late Young Female Single Yes No R mand. M16 Late Mid Male Single Yes No L max. M18 Late Mid Male Group (4, 5, 7) Yes No L mand. M19 Late Mid Female Sim. (10, 12) Yes Yes R max. M1

10 Late Young Male Sim. (9, 12) Yes Yes L mand. M111 Early Mid Male Single Yes No L mand. M112 Late Young Female Sim. (9, 10) No No R max. M116 Late Mid Male Sim. (17) No No R max. M117 Late Young Female Sim. (16) No No L max. M119 Late Adult Male Single Yes No L max. M120 Early Mid Male Group (21) No No R max. M122 Late Young Female Single Yes No R max. M124 Late Young Male Sim. (25) Yes No L max. M127 Late Mid Female Group (31, 32) Yes No L max. M130 Late Mid Male Group (44) Yes Yes L max. M131 Late Young Female Sim. (27, 32) No No L max. M132 Late Mid Male Sim. (31), Group (27) No No L mand. M134 Late Mid Male Single No No R mand. M135 Early Young Male Group (40) No No L mand. M137 Late Subadult ? Single Yes No R mand. M138 Early Mid Female Group (26, 23) Yes No R max. M140 Early Young Male Group (35) No No L max. M142 Late Subadult ? Group (43) No No R mand. M143 Late Mid Female Group (42) No Yes R mand. M144 Late Young Female Group (30) No No R mand. M1

Fig. 3. Distribution and sex of early and late burials at the Nebira site. Key: (M) = male, (F) = female, (sa) = subadult, (?) = unknown sex, ? = unknown burial number. Adaptedfrom Bulmer (1978).


decomposition. Natural decomposition may also have caused dis-articulation of bones and cannot be ruled out as a cause. The re-moval of bones post-mortem was also noted with the lefthumerus, ulna and radius removed from burial 11.

The majority of individuals were buried on their back (supine)with only a few lying on their side. Burials from both early (78%)and late (43%) phases had burial goods associated with themincluding various shell ornaments, bone ornaments, pottery and

Fig. 4. Selection of bone, tooth and shell artefacts associated with the burials at Nebira. From Bulmer (1978).


a range of other shell and stone artefacts (Fig. 4). There is some var-iation in the orientation of the graves, although they are largelyorientated with the head toward the west and southwest (Bulmer,1978; Fig. 3). Collectively, the burial customs of the people living atthe Nebira site indicate there may be some differentiation withinthe burial ground based on burial goods and burial type.

Radiocarbon determinations date initial occupation at the baseof the Nebira hill to around 1760 BP (Allen, 1972). However, theNebira hill saddle was not used as an occupation area and burialground until ca. 720–300 BP (Bulmer, 1978; Pietrusewsky, 1976).The burials therefore date to a period when there was a largepopulation increase in the area, the introduction of new ceramic

traditions and the establishment of large scale, complex trade sys-tems in the region, which may indicate the beginning of the Hiritrade (Table 2). Although there is some temporal variation in thedates for the Nebira burials (ca. 400 years), it has been suggestedthat the chronological period in which most of the burials weredeposited was over a relatively short period of time (Bulmer,1978). It is possible that there is as much as 400 years differencebetween early and late burials, though this remains untested.

A possible explanation for the hilltop settlement of Nebira wasfor defensive purposes (Bulmer, 1978, 1979). Bulmer (1979) arguesthat the Nebira settlement was relocated from the base of the hillto the saddle area around the time of increased population


pressure in the area as a possible response to land warfare. Recentresearch on the skeletal evidence of trauma in the Nebira individ-uals by Scott and Buckley (2010) found that nine of the 28 sampledindividuals from Nebira had evidence of skeletal trauma. Six of theskeletons (five men and one woman) had healed cranial fracturesconsistent with sharp-force and blunt-force trauma. Scott andBuckley (2010) note that the level of trauma in the Nebira skeletalsample is relatively high compared with other skeletal studies oftrauma worldwide and suggest that it may reflect tribal warfarein the area during the hilltop occupation of Nebira.

Radiogenic/stable isotope and trace element concentration analyses

Strontium isotopesThe application of 87Sr/86Sr isotopes in archaeological research

to determine migration has been used for over 20 years (Ericson,1985, 1989). It is based on the premise that strontium from thegeological environment is ingested via food and water and retainedmainly in the skeletal and dental tissues. When measured in toothenamel, the isotopic signature will reflect the food and water in-gested during the timing of its formation during childhood. There-fore the isotopic signature in tooth enamel also provides apermanent record of the individual’s environment, and conse-quently their geographic location during this childhood period.The principles and further details of radiogenic/stable strontiumisotope analysis as an indicator of prehistoric migration have beendescribed in detail elsewhere and will not be reiterated here (Bent-ley, 2006; Price et al., 2002).

The application of strontium isotopes to determine migration isdependent on the ability to distinguish between local and poten-tially non-local individuals (Bentley et al., 2004). In many cases,the strontium isotope variation in the underlying geology has beenused to characterise the local area or catchment where the archae-ological site is situated (Ezzo et al., 1997; Grupe et al., 1997). Shawet al. (2009) have provided a summary of the strontium isotopevariation in the Pacific Island groups of the region, illustrated inFig. 5. In areas like New Guinea which contain a complex mixtureof geological substrates with no definable boundaries (see Fig. 2)

Fig. 5. Strontium isotope variation in geological samples in Papua New Guinea and isla

this technique may be less effective at suitably characterising a lo-cal signature.

The use of domesticated animals as a local proxy for identifyinghuman migration somewhat revolutionised the process of estimat-ing local human strontium variation. This method is based on thepremise that animal domesticates live in close proximity to theassociated human population, reflecting the natural isotope varia-tion near the prehistoric settlement (Bentley et al., 2004). How-ever, in a Pacific Island context it has been demonstrated thatusing pigs as a local proxy for the human population is not appro-priate (Shaw et al., 2009, 2010). Pacific Island pigs are knownarchaeologically to have been a valuable trade item in prehistoricexchange systems. Consequently, there was a high level of mobilityin the life span of these specific domesticates, reflected in greatervariability in their isotopic signatures.

While other animals (such as wallabies, rats or dog) would alsobe useful for estimating a local range in New Guinea, no animalteeth were available for isotopic analysis. Instead, calculating atwo standard deviation cut off point from the sample mean ofthe human population may provide a more reliable first order esti-mate of the isotopic variation in the local population. The two stan-dard deviation method has been applied widely in archaeologicalresearch elsewhere (Evans et al., 2006a; Price et al., 2002; Slovaket al., 2009; Turner et al., 2009). However, it is recognised thatusing a two standard deviation range will not define the local iso-topic variation with absolute certainty. Therefore the mean of thesample will also be presented in an attempt to estimate the localsignature.

Oxygen isotopesOxygen isotopes (d18O) have been used in archaeological re-

search to assess seasonal activity patterns (Balasse, 2003; Balasseet al., 2002; Kennett and Voorhies, 1996) and migration in prehis-toric populations (Evans et al., 2006a,b; Knudson et al., 2009). Theuse of oxygen isotopes to determine prehistoric migration isdependent on the ability to identify variation in the precipitationwithin the study region. The oxygen composition of water isdependent on geography and climate and decreases with relativelylower temperatures, increasing distance from the sea, and

nd groups composed of or derived from continental rock. From Shaw et al. (2009).


increasing elevation of an individual’s place of residence (Bryantet al., 1996; Kohn et al., 1996; Longinelli, 1973, 1984; Sponheimerand Lee-Thorp, 1999).

In a Pacific Island context the d18O (‰ V-SMOW) of precipita-tion is largely consistent (�6 ± 2‰) throughout the Western Is-lands as a result of the prevailing Trade Winds in the region(Bowen and Revenaugh, 2003; Bowen and Wilkinson, 2002).Therefore, within the island of New Guinea the main contributingfactor to oxygen isotope variation is distance from the sea and alti-tude. This is particularly relevant for Nebira as those individualsthat resided inland most probably obtained water draining fromthe nearby Astrolabe range (ca. 800 m a.s.l). On the other hand,non-local individuals may have obtained water from anothersource. Oxygen isotope values obtained from human and pig teethfrom island environments in the Bismarck Archipelago and Vanua-tu where the elevation is considerably less than mainland PapuaNew Guinea averaged between 23.9 and 24.7 (see Table 1). Itwould therefore be expected that water draining from the higherOwen Stanley Range near Nebira would yield lower values thanthose obtained in an island environment.

Yet, the geographic division between coastal and inland settle-ment is complicated by the fact that individuals living elsewheremay have also been drinking water flowing from the same sourceas individuals living inland, on the coast and at higher altitudes.Furthermore, oxygen isotopes can vary considerably within a pop-ulation, and within a single individual, due to differences in phys-iology and localised water sources (Kohn et al., 1996). This makesidentifying local and non-local individuals in a Pacific Island envi-ronment based on oxygen isotopic data alone very difficult. Oxygenisotope data therefore needs to be interpreted with caution.

Unlike strontium isotopes, a two standard deviation cut off isnot used to estimate the ‘local’ range in a sample population dueto the unknown degree of natural oxygen isotope variation in a sin-gle localised environment. Instead, a clustered group of individualswith similar values can be used cautiously to determine the localpopulation, as was applied with the Lapita skeletal sample fromTeouma in Vanuatu (Bentley et al., 2007b). This method will beused in this paper to assess whether the oxygen isotopes are vari-able enough to identify non-local individuals on the mainland ofPapua New Guinea. A considerable amount of further researchneeds to be conducted to compile a detailed map of oxygen isotopevariation in New Guinea to better understand the degree of local-ised variation if this technique is to be used in future archaeologi-cal research.

Barium and strontium trace elementsBarium and strontium trace element concentrations (Ba/Sr) in

human bone and tooth enamel have been used in previous archae-ological research as a method for estimating the marine vs. terres-trial component in a prehistoric diet (Arnay-de-la-Rosa et al., 2009;Burton and Price, 1990, 1999; Horwood, 1988). Both of the elemen-tal concentrations are measured relative to calcium and are there-fore representative of the calcium component of the diet (Burtonand Price, 1990, 2000). Generally, as seawater has Ba/Sr valuesmuch lower than most terrestrial environments (by as much asthree orders of magnitude) fish and other creatures living in sea-water will also have lower Ba/Sr signatures than most terrestrialfoods (Burton and Price, 1990). A low Ba/Sr signature in tooth en-amel may then, parsimoniously, be suggestive of a marine baseddiet. However, it is also likely to represent a change in trophic levelso Ba/Sr cannot be used as a quantitative measure of seafood in thediet (Burton, 2008).

In a Pacific Island context, seafood would be a major contributorto a higher strontium concentration (Horwood, 1988; Leach et al.,2003). Strontium ingested from a high seafood diet can contributeto the 87Sr/86Sr composition and potentially mask the geological

strontium signature used to infer migration. Therefore, the Ba/Srtrace element concentration ratio is used in this study to assessthe possible influence of marine foods in the individual’s diet priorto the interpretation of migration using the strontium isotopicdata. The Ba/Sr elemental composition is used only as an estimatedindicator of dietary input because while seafood is a major influ-ence on a low Ba/Sr signature, it is acknowledged that several die-tary inputs may result in a similar signature. Consequently, a twostandard deviation range is also presented for this data only asan indicator of variation in the Nebira sample, rather than as anestimate of a local range.

Plants such as Pandanus fruits (Pandanus spp.), Cordyline root(Cordyline spp.), banana (Musa spp.) stems, yam (Dioscorea spp.)and a wide range of other tubers grown on limestone derived soilsmay also contribute to an increase in strontium ingestion. Lime-stone and uplifted reef deposits are common in areas adjacent tothe New Guinea coastline (Löffler, 1977). Barium is commonly low-er in limestone than in terrestrial derived rock, and when com-bined with high strontium levels results in a lower Ba/Sr ratio(Faure and Powell, 1972). In contrast, volcanic derived and conti-nental rock formations typical in New Guinea are generally en-riched in barium (Page and Johnson, 1974; Smith and Compston,1982). If seafood was not an important component of anindividual’s diet then the strontium isotope signature from thesame individuals may be used as a geological, and therefore as ageographical signature, rather than a possible by-product of havingelevated strontium from a large marine dietary component(Bentley et al., 2007b; Burton and Price, 1990).

Diagenesis

The change in chemical composition of skeletal and dental tissueafter its interment in the ground is an issue that needs to be con-trolled before any meaningful interpretation can be made usingchemical analyses. Although the process and methods of controllingdiagenetic alteration have been outlined by others (Budd et al.,2000; Koch et al., 1997) the steps taken to control diagenesis inthe Nebira sample first need to be outlined. It is well known thatbone is more susceptible to post-mortem chemical alteration thanteeth, even after relatively short periods of time (Bentley, 2006; Priceet al., 1992). The exclusive use of dental enamel in this study avoidsthe issues of diagenesis that are inherent with the use of bone.

Enamel is made up of ca. 97% inorganic material that lack bothcellular components and blood supply (Hillson, 1990). The primarymineral in enamel is hydroxyapatite, a naturally occurring crystal-line calcium apatite containing high amounts of carbonates andphosphates (Hillson, 1990). Hydroxyapatite is densely packedwithin the enamel and is arranged in a non-porous rod likearrangement to withstand the forces of chewing (Hillson, 1996).The bundled rod structure of enamel and the large inorganic com-ponent renders it extremely resistant to mechanical erosion, and topost-mortem contamination (Hoppe et al., 2003). Surface abrasionand chemical leaching, as described below, was also undertakenbefore analysis to remove surface contaminants adhering to theenamel from the burial environment. In addition, the reasonablepreservation of the dental remains suggests that post-mortemalteration had not significantly affected the integrity of the dentaltissue.

Methods

All individuals with first permanent molars were included inthe sample for radiogenic/stable isotope and trace element concen-tration analyses. The first molar was chosen because the enamel ofthis tooth begins development in utero and finishes around


2.5 years of age, and is therefore more likely to represent an indi-vidual’s place of birth (Hillson, 1990; White and Folkens, 2005).Any subsequent change in residence should be able to be detectedthrough the different geological signature compared with localindividuals (Bentley, 2006). Migration could have occurred priorto this age (presumably assisted by the individuals parent or care-giver) and would be undetectable, however, the selection of a toothwhich develops relatively early in childhood limits the impact ofthis unavoidable issue. This sampling strategy has been used inprevious research for these reasons (Ezzo and Price, 2002; Priceet al., 2006a).

A tooth was only sampled if provenance to a specific burial wascertain. Only first molars that had completed crown developmentwere used to avoid issues such as diagenesis with the burial envi-ronment due to incomplete tooth mineralisation (Budd et al.,2000). This sampling strategy ensured the inclusion of individualsof different ages (at time of death) and the representation of bothsexes. In total, 27 first molars were available for the radiogenic/sta-ble isotope and trace element concentration analyses (Table 3;males = 15, female = 10, subadult = 2). The Nebira sample thereforerepresents the largest Pacific Island sample to be analysed isotopi-cally for migration to date (see Table 1 for comparison).

Procedure

The teeth samples were mechanically prepared and analysedfor strontium isotopic composition and the Ba/Sr elemental ratioin the Centre for Trace Element Analysis at the University of Otago.Oxygen isotopes were analysed in the iso-analytical laboratory inCheshire, England. Whole teeth were cleaned under tap water witha toothbrush to remove any superficial dirt or staining and dried atroom temperature before mechanical preparation. All teeth se-lected for isotopic analysis were recorded and photographed be-fore removing the enamel. Teeth were mechanically preparedand the enamel sampled using the method described in Shawet al. (2010). Enamel samples weighing between 45 and 100 mgwere obtained. Because oxygen isotope analysis requires an intactenamel sample whereas strontium isotope and Ba/Sr analysis re-quires enamel to be dissolved, the enamel sample from each toothwas divided into two for the separate analyses.

Strontium isotope analysisEach enamel sample was weighed into a PFA vial prior to disso-

lution with quartz-distilled 3 N HNO3. Strontium was extractedfrom the sample matrix using a two-stage ion exchange separationprotocol using Eichrom

�Sr-SPEC resin and a modified version of

the established method by Pin and Bassin (1992). After elution,the strontium fraction was stored in 0.25 N HNO3 in preparationfor mass spectrometric analysis. The 87Sr/86Sr isotopic compositionwas determined by Multiple-Collector Inductively Coupled PlasmaMass Spectrometry (MC-ICPMS) using a Nu Plasma-HR MC-ICPMSinstrument (Nu Instruments Ltd., UK).

The strontium isotopic standard (NIST SRM 987 Sr) was ana-lysed repeatedly throughout the course of the measurement ses-sion to assess the veracity of the analyses. Twenty-fivemeasurements of this standard yielded an average 87Sr/86Sr valueof 0.710286 ± 0.000013 (1r), in very good agreement with the ac-cepted value of 0.71034 ± 0.00013 (1r) (Moore et al., 1982). Fur-thermore, repeat measurements (N = 5) of an in-house Tridacnacarbonate standard (sourced from the Australian National Univer-sity) gave rise to an average 87Sr/86Sr value of 0.70920 ± 0.000006(1r), in excellent agreement with the composition determinedfor present day open-ocean water of 0.7092 (Burke et al., 1982;Veizer, 1989). Duplicate analyses were also performed on threesamples which ranged between ±0.000013 and 0.000027 (2 SE).

Total procedural blanks for the chemical separation process were60.05 ng which is negligible.

Ba/Sr analysisPreparation of Ba/Sr samples required the same leaching and

dissolving steps as strontium isotope analysis. No further chemicalpreparation was performed on the trace element samples otherthan dilution to suit the analytical range of the instrument. TheBa/Sr trace element concentration was determined by QuadrupoleInductively Coupled Plasma Mass Spectrometry (Q-ICP-MS). Sam-ples were introduced in 0.05 N HNO3. Replicate measurements ofone enamel sample were acquired throughout the sample analysissession in order to assess instrumental drift during the analysissession and the reproducibility of the sample analyses, producingan average Ba/Sr value of 0.015 ± 0.0004 (2 SD). Because the Ba/Sr ratios of a marine dominated diet is lower than that of a terres-trial dominated diet by a few orders of magnitude all Ba/Sr valueswere transformed into a logarithm form.

Oxygen isotope analysisSample preparation of tooth enamel for d18O followed an estab-

lished pre-treatment procedure presented by Koch et al. (1997)using NaOCl and acetic acid. Tooth enamel was ground to a roughpowder using a pestle and mortar and transferred into acid cleanedglass vials. The samples were soaked in 2% NaOCL (sodium hypo-chlorite) for 24 h, rinsed in Milli-Q water and soaked in 0.1 M ace-tic acid for another 24 h to remove organic and secondarydiagenetic carbonates in the tooth enamel. Pre-treatment resultedin the enamel samples typically weighing between 20 and 50 mg.Oxygen isotopes were measured in the carbonate component ofthe tooth enamel, relative to V-PDB, using Continuous Flow IsotopeRatio Mass Spectrometry (CF-IR-MS). During sample analysis, re-peated analyses of the calcium carbonate international referencestandards NBS-18 (N = 2) and NBS-19 (N = 2) yielded mean valuesof �23.18 ± 0.1‰ (1 SD) and �2.2 ± 0.02‰ (1 SD) respectively.The d18O data was converted from V-PDB to V-SMOW using theequation d18OVSMOW = (1.03091 � d18OV-PDB) + 30.91 presented inCoplen (1983: p. 237). This conversion allows the results presentedin this paper to be comparable with previous migration-based iso-topic studies in the Pacific Islands (Bentley et al., 2007b).

Results

The results of the 87Sr/86Sr, Log(Ba/Sr) and d18O analyses arepresented in Table 4 for the Nebira tooth samples.

The Nebira samples (N = 27) had a mean value of 0.70630 for87Sr/86Sr, 23.5 for d18OVSMOW and �1.33 for Log(Ba/Sr). The twostandard deviation range was 0.70799–0.70460 for 87Sr/86Sr,24.6–22.4 for d18OVSMOW and �1.67 to �0.98 for Log(Ba/Sr). Burials6 and 22 fell outside the two standard deviation range for stron-tium isotopes when calculated using all samples (Fig. 6, greybox). Burials 9 and 35 exhibited the most extreme oxygen isotopevalues in the sample, higher and lower than the remaining Nebirasamples respectively (Fig. 7).

Two groups cluster together with the strontium isotope data(Fig. 6). The majority of the Nebira individuals (N = 22) groupedaround a mean strontium isotope value of 0.70593, a meanLog(Ba/Sr) value of �1.36 and a mean d18OVSMOW of 23.5. However,five individuals were grouped separately from the other 22, includ-ing two men (B34 and B6), two women (B22 and B3) and a suba-dult with a fully developed permanent first molar (B42). Thesefive individuals yielded a mean strontium isotope value of0.70792. The mean Log(Ba/Sr) value of the five individuals was alsoslightly higher than the rest (�1.17), falling toward valuesobtained for a mixed diet of marine/terrestrial foods.

Table 487Sr/86Sr, d18O and Log(Ba/Sr) data from the burials at Nebira. Typical analytical errorsfor individual measured values are: 87Sr/86Sr = 0.000014 (±2 SE), d18O = 0.1 (±1 SE)and Log(Ba/Sr) = 0.0004 (±1 SE).

Burial 87Sr/86Sr d18OV-PDB(‰) d18OVSMOW Ba/Sr Log(Ba/Sr)

1 0.70572 �6.9 23.8 0.024 �1.622 0.70557 �7.7 23.0 0.023 �1.643 0.70775 �6.5 24.2 0.065 �1.196 0.70826 �7.5 23.1 0.072 �1.148 0.70588 �6.8 23.9 0.050 �1.309 0.70625 �5.6 25.1 0.077 �1.11

10 0.70583 �7.1 23.6 0.062 �1.2111 0.70583 �7.2 23.5 0.054 �1.2712 0.70577 �6.9 23.9 0.035 �1.4616 0.70597 �6.7 24.1 0.057 �1.2417 0.70555 �7.1 23.6 0.067 �1.1719 0.70596 �7.4 23.3 0.065 �1.1920 0.70601 �7.1 23.6 0.050 �1.3022 0.70830 �7.3 23.3 0.052 �1.2824 0.70563 �7.5 23.2 0.049 �1.3127 0.70664 �7.4 23.3 0.036 �1.4430 0.70656 �6.9 23.8 0.046 �1.3431 0.70619 �6.5 24.2 0.035 �1.4632 0.70592 �7.1 23.6 0.045 �1.3534 0.70786 �7.1 23.6 0.049 �1.3135 0.70584 �8.3 22.3 0.021 �1.6837 0.70548 �7.9 22.8 0.044 �1.3638 0.70623 �7.6 23.1 0.025 �1.6040 0.70572 �7.8 22.9 0.044 �1.3642 0.70744 �7.6 23.1 0.112 �0.9543 0.70579 �7.4 23.3 0.041 �1.3944 0.70606 �7.7 23.0 0.069 �1.16


87Sr/86Sr local range for the Nebira site

The clear division between the majority of the individuals(N = 22) and the five outliers in the strontium isotope values re-quired some consideration before calculating the two standarddeviation local ranges for Nebira. Based on the clear separation be-tween the two groups, the five outliers were excluded from the cal-culation of the two standard deviation range (Black box in Figs. 6and 7). The two standard deviation range for the Nebira sampleexcluding the five outliers was 0.70653–0.70533 for 87Sr/86Srwhich resulted in a further two individuals (B27 and B30) fallingoutside this range.

Fig. 6. 87Sr/86Sr vs. Log(Ba/Sr) for the Nebira tooth enamel samples. The value for seawa(Log Ba/Sr) in a coastal environment is shown for comparison, data from Burton and Pricfrom the mean for 87Sr/86Sr vs. Log(Ba/Sr) of all samples. The black box indicates 2 SD fromwithin the samples symbol. Key: d = male, N = female, j = sub adult. Outliers are labell

Discussion

Non-local individuals and potential origins

Based on the radiogenic/stable isotope and trace element con-centration data there appear to be two major groups of individualsclustering around 87Sr/86Sr values of ca. 0.7060 and ca. 0.7080respectively. It is likely that the larger group of individuals cluster-ing around 0.7060 are local to the site because Nebira is situated onEocene and Oligocene gabbro (Allen, 1972, see Fig. 2), which typi-cally yields similar strontium isotope values to those observed inthe larger group (Smith and Compston, 1982). Therefore, it is morelikely that the group of five individuals (B3, B6, B22, B34 and B42)came from somewhere other than the immediate vicinity of Nebi-ra. Based on the elevated strontium isotope values of these mi-grants, it is possible these individuals came from a locationcloser to the coast than Nebira.

Origin of the five non-local individuals

It is also possible that the elevated strontium isotope values ofthese five individuals may have resulted from consuming a highmarine diet. When considering the trace element concentrationdata, these five individuals have Log(Ba/Sr) values similar to the lo-cal majority from Nebira, falling within the range of a generallymixed terrestrial/marine diet. These values suggest that the cal-cium component of their diet and/or differences in the trophic cy-cle in their respective environment did not significantly contributeto the observed elevated strontium isotope values. The highestLog(Ba/Sr) value came from the non-local subadult (B42). Withthe exception of this individual, there was no discernable differ-ence in the Log(Ba/Sr) values between the local and non-localindividuals.

Wild and cultivated plants consumed along the South Coast inprehistory will have absorbed nutrients and trace elements fromthe underlying geology. Animals such as pig and wallaby will havealso been exploited but would not contribute as significantly to theoverall strontium content in the diet. With the similarity in thetrace element data between the local and non-local individuals, itis possible that plants consumed by the non-local individuals mayhave been enriched in strontium from the sea and/or limestonedeposits influencing the isotopic values without impacting greatly

ter (87Sr/86Sr) and the mean ± 2 SD for a predominantly marine and terrestrial diete (1990). The area in between represents a mixed diet. The grey box indicates 2 SD

the mean excluding the five outliers discussed in the text. Measurement errors falled.

Fig. 7. 87Sr/86Sr vs. d18OVSMOW for the Nebira burial tooth enamel samples showing average seawater value for comparison. The grey box indicates 2 SD from the mean for87Sr/86Sr vs. d18OVSMOW of all samples. The black box indicates 2 SD from the mean excluding the five outliers discussed in text. Measurement errors fall within the samplessymbol. Key: d = male, N = female, j = sub adult. Outliers are labelled.


on the concentration data. However, it is likely that a number ofinfluencing factors would have contributed to the pattern observedin the data between the local and non-local individuals.

From the chemical analyses it is proposed that five non-localindividuals were immigrants who came from a coastal origin oran origin closer to the coast than the site of Nebira. Strontium fromsea spray (ca. 0.7092) entering soils on the coast would result in anelevated strontium isotope signature when ingested by individualsconsuming seafood, plants grown on coastal soils and animalsraised in a coastal environment. Uplifted limestone outcrops alongthe coast (Löffler, 1977) may have also contributed to an elevatedstrontium isotope signature, as strontium isotopic values in lime-stone are also close to, or identical to 0.7092 (Faure and Powell,1972). However, the strontium isotope signatures in the non-localgroup of five individuals is still lower than values expected fromindividuals living on a limestone dominated environment, as illus-trated in Shaw et al. (2010). It therefore appears that these individ-uals did not come from an environment completely dominated bymarine limestone but perhaps from an environment where lime-stone comprised a large proportion of the localised geology.

It has also been found that biologically available strontium inthe Pacific Islands exhibits a mixing system within tooth enamel,producing an averaging effect between multiple strontium sources(Shaw et al., 2009, 2010). Based on this premise, an environmentcomposed of a mix of limestone (ca. 0.7092) and terrestrial derivedsedimentary deposits (ca. 0.704–0.705) would be more likely toproduce the intermediate strontium isotope values observed inthe group of five non-local individuals from Nebira. At this stage,an island origin for these individuals cannot be ruled out basedon the current data.

Other notable individuals

Two individuals (B35 and B9) had oxygen isotope values lowerand higher than the majority of the sample respectively and re-quire further consideration. The two standard deviation range forthe Nebira sample was 24.7–22.3‰ with a range of 2.4‰, whichis larger than that observed for the variation in precipitation acrossthe entire Western Pacific Island region (Bowen and Wilkinson,2002). Individuals falling outside either end of this range may haveobtained their drinking water from a source further away or closerto sea level than the local majority. It is possible that B35 and B9came from two separate locations, or at least one of theseindividuals was non-local to Nebira. However, as stated earlier,

the oxygen isotope data is equivocal without the analysis of furthersamples and detailed isotope mapping of the South Coast.

The exclusion of the five outlying individuals from the calcula-tion of the two standard deviation local range for strontium iso-topes resulted in a further two individuals considered aspotential non-local individuals, those of B27 and B30. It is possiblethese two individuals were not born at Nebira. Although it is alsounlikely they originated from the coast, as a coastal signaturewould be elevated more toward that of seawater (ca. 0.7092).The oxygen isotope values of these two individuals are the sameas the local majority indicating they may have obtained drinkingwater from a similar catchment or source as the Nebira locals. Itis tempting to suggest that these two individuals may be non-localto Nebira but this conclusion would be largely unsubstantiatedwithout the analysis of more samples.

Problems with defining ‘local’ and ‘non-local’ individuals at Nebira

The strontium isotopes measured in the Nebira sample indicatethat five individuals (18%) within the sample may have beennon-local to the site (Figs. 6 and 7). There is some variation inthe oxygen isotope data within the Nebira sample but was notlarge enough to rule out natural variation within the individualand the population. Therefore, the oxygen isotope data cannot beconsidered to specifically reflect migration at Nebira without theanalysis of additional samples.

The application of isotope analyses to the Nebira skeletalassemblage raises several important considerations for the isotopicidentification of non-local individuals in a Pacific Island environ-ment. The most pressing issue is the difficulty of characterisingthe local strontium and oxygen isotope values due to the complexgeological makeup of mainland New Guinea. The geology and geo-morphology along the South Coast is a complex mosaic of conti-nental rock and uplifted limestone that extends discontinuouslyinto the Owen Stanley Range behind Nebira (Löffler, 1977; seeFig. 2). While groups of individuals can be clearly identified usingstrontium isotopes, the division between these same individualsusing oxygen isotopes is less clear. To better understand the levelof biologically available radiogenic/stable isotopic variation in theenvironment surrounding Nebira, further human and animal teethsamples need to be analysed which will provide an average for allthe combined strontium isotopic sources. The analysis of soil andplant samples along the coast would also be an informative, butextensive exercise.


The question of ‘what is defined as local?’ must then be ad-dressed. Again, the analysis of more teeth samples may clarify thisissue to some degree, particularly from archaeological sites in thevicinity of Nebira. Interestingly, there was more strontium isotopevariation in the local and non-local individuals identified at Nebirathan in the geological substrates sampled throughout Papua NewGuinea and Island Melanesia (see Fig. 5). The range of strontiumisotope values in the Nebira sample is encouraging as it illustratesthat more variation exists in biologically available strontium in Pa-pua New Guinea than the geological data indicates.

The identified variation may therefore be related to movementof people from different geological/geographical regions, ratherthan localised natural variation. The isotopic variation in the Nebi-ra population provides an opportunity to begin to define distinctisotopic regions on the New Guinea mainland with the hope ofidentifying non-local individuals, and perhaps their origins. Ulti-mately, it remains unclear as to whether non-local individualsidentified at Nebira came from nearby or potentially distant ori-gins. Yet identifying non-local individuals at an archaeological siteis still informative when addressing questions of interaction. How-ever, the possibility of identifying non-local origins would havevery important implications for understanding more specific socialinteraction and cultural development in future applications.

Addressing the ‘outstation’ hypothesis

The isotopic data presented in this paper suggest that five indi-viduals moved, or migrated, to Nebira from a potentially coastallocation sometime after late childhood and were eventually in-terred at the site. Unfortunately at this stage, despite the clear divi-sion in the strontium isotope dataset the origin of these individualsis difficult to pinpoint given the limited understanding of isotopicvariation along the South Coast. It would be interesting to attemptto source the origins of the non-local individuals and any tradedmaterial culture in future research to determine if they both camefrom a similar area. Nonetheless, movement to Nebira from thecoast supports the basic premise of the ‘outstation’ hypothesisput forth by Allen (1972) who, along with Bulmer (1978), sug-gested that Nebira acted as a reciprocal trading post between in-land and coastal communities.

However, the ‘Outstation’ hypothesis is a simplistic model anddoes not explain the need for these individuals to migrate beyondthe basic requirement to transport exchange goods to Nebira.Other incentives for migration include marriage, famine and war-fare among countless others. Unfortunately given the small num-ber of comparable skeletal remains from sites along the SouthCoast, these possibilities will remain untested in the foreseeablefuture. The scenario presented here does suggest that there wasa ‘biological transfer’ occurring at the site of Nebira as the migra-tion of people would facilitate the genetic mixing of culturalgroups along the South Coast. The presence of immigrants in theNebira cemetery from a coastal location suggests that the peopleliving at Nebira were associated to some extent with other com-munities in the region.

Social identity of the non-local individuals

When the isotopic evidence for migration is correlated with thebiological and burial treatment data within the burial ground, sev-eral points can be inferred about the social identity and nature ofinteraction of the five non-local immigrant individuals interred atthe Nebira site. Firstly, all five individuals identified as non-localto Nebira are late period burials. This is not unexpected as migra-tion would have been common during this period of high mobility,as identified through the increase in non-local pottery during occu-pation at the site. However, the burial data indicates that the

majority of the sampled individuals were late period burials(N = 22/27) so no meaningful association between migration andburial period can be made.

Secondly, as mentioned above, a number of interments con-tained multiple individuals (simultaneous burials) or were buriedin close proximity to other individuals (group burials) which hasbeen suggested to indicate familial relationships (Bulmer, 1978;Pietrusewsky, 1976) (Fig. 3). The group of five individuals identi-fied from strontium isotopes as having immigrated from the coastare almost all single burials, with four clearly interred in this way(B3, B6, B22 and B34). This group comprises of two young femalesand two middle aged males. It is interesting that both males andfemales of differing age at death were non-local to the site, indicat-ing that the pattern of immigration was not specific to sex or age.The only possible exception to this pattern is the non-local suba-dult (B42) who was interred in proximity to burial 43, a local mid-dle aged woman. Bulmer (1978) noted that the grave cut of burial43 cut into burial 42 and was a later addition to the burial ground.Taking this into consideration, there is no significant correlationregarding burial type between group/simultaneous internments,or single interments (P-value = 1, two tailed Fisher’s exact test).

Thirdly, grave goods were present with both local (n = 12/22)and non-local (n = 3/5) burials. The type of grave goods presentin each of the graves was variable, with some graves more richlyadorned than others. A necklace of human hand phalanges froman unknown individual/s was placed around the neck of B9, theonly noted case of human remains used as a burial good, makingthis female distinctive in burial treatment compared to others atNebira. However, there is no significant association between thepresence of grave goods and migration in the Nebira sample (P-va-lue = 1, two tailed Fisher’s exact test).

Lastly, further insight may be gained on the possible violentinteractions between Nebira and other communities using the re-cent trauma data provided by Scott and Buckley (2010). Of the sixindividuals identified as having healed cranial trauma consistentwith violence, all were also sampled for isotope and trace ele-ment concentration analysis (B2, B9, B10, B24, B30 and B43).None of these individuals were considered non-local based onthe data presented in this paper. One identified non-local individ-ual (B34) had a fractured second metacarpal on the left footwhich had evidence of remodelling. A fractured metacarpal iscommonly identified in prehistoric populations and does not haveany direct correlation with inter-personal violence. However, therepresentation of cranial trauma in local individuals only isintriguing; with the presence of healed trauma indicating that itwas not the cause of death in these individuals (Scott andBuckley, 2010). The correlation may be suggestive of relativelylocalised violence between communities but is also equally aslikely to be attributed to generally high levels of inter-personalviolence in the region at this time.

Conclusions

Nebira was occupied during and after the period of large scalecolonization along the South Coast of Papua New Guinea by anintrusive group of people, with the uphill part of the site beingused as a burial ground between ca.720–300 BP. The archaeologicalevidence indicates that during the time the burial ground wasused, complex trade and communication networks were estab-lished throughout the South Coast with settlements acting as hubsof interaction, of which Nebira was likely one of them. Allen (1972)suggested that, at least during the early period of occupation, theinland location of Nebira was of an economic advantage throughreciprocal trade with coastal communities, the so-called ‘outsta-tion’ hypothesis.


The isotope and trace element concentration data reported inthis paper support the basic premise of the ‘Outstation’ hypothesisby providing evidence for a group of five individuals migrating toNebira, argued as coming from a coastal location. However thehypothesis does not fully explain the need to migrate, which cur-rently remains unidentified. The analyses also highlighted a num-ber of issues surrounding the application of isotopic techniques ina Pacific Island–Papua New Guinea context. While these issues lim-it the information potential regarding understanding prehistoricmigration, it more importantly identifies areas that require re-search in the future. Current isotopic based archaeological researchis now being undertaken in other areas of the Pacific Islands to ad-dress the issues identified in this paper.

The non-local individuals were from late period burials withinthe Nebira cemetery, suggesting that migration was common laterin prehistory, possibly during and after the development of largescale trade and exchange networks along the South Coast. Further-more, the mortuary context of the burials indicates that the non-local burials were all single interments, with the possible excep-tion of B42 whose burial context may be disturbed. No obviousfamilial connections between local and non-local individuals wereidentified in the Nebira sample. Although a pattern appears to beemerging with the majority of single burials belonging to non-localindividuals, this cannot be substantiated based on the current data.

The identification of non-local individuals in the Nebira skeletalassemblage is only the first step in understanding the social devel-opment of this prehistoric population. More importantly is theinterpretation of migration as a social process. As such, combiningbiological and archaeological data has allowed a much more de-tailed understanding of the social context associated with prehis-toric migration in the Nebira population. The isotope and traceelement concentration analysis of samples from other prehistoricpopulations along the South Coast will greatly contribute to the re-sults obtained in this paper, and may allow for further interpreta-tion of these results in future research.

Acknowledgments

The authors wish to thank Herman Mandui and the Papua NewGuinea National Museum and Art Gallery for giving permission toundertaken the analyses presented in this paper. Thank you toDavid Barr for running the trace element concentration analysisfor the teeth samples. We thank the Australian National Universityfor kindly providing the Tridacna standard. We gratefully acknowl-edge the Community Trust of Otago for financial support to theCentre for Trace Element Analysis. Thanks also go to Tanja (TJ)Harding, Sean P. Connaughton and Rebecca Kinaston for readingprevious drafts of this paper and providing valuable feedback.

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