Early urbanization and mobility at Tell Brak, NE Syria: the evidence from femoral and tibial external shaft shape

HOMO - Journal of Comparative Human Biology 66 (2015) 101–117

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Early urbanization and mobility at Tell Brak, NE Syria: the evidence from femoral and tibial external shaft shape Arkadiusz Sołtysiak ∗ Department of Bioarchaeology, Institute of Archaeology, University of Warsaw, Krakowskie Przedmie´scie 26/28, 00-927 Warszawa, Poland

a r t i c l e

i n f o

Article history: Received 23 January 2014 Accepted 8 September 2014

a b s t r a c t Urbanization at Tell Brak began in the late 5th millennium BCE and the site reached its maximum size in the Late Chalcolithic (LC) 3, ca. 3900–3600 BCE. During that time, a large midden was formed at the edge of the early city, now known as Tell Majnuna. Rescue excavations at Tell Majnuna revealed several clusters of commingled human remains and a cemetery on the top. Several human skeletons dated to the LC 3 and Early Bronze Age (EBA) were found also at Tell Brak itself and it was possible to investigate differences in cross-sectional femoral and tibial shaft shapes between LC 3 and EBA to test the hypothesis that rapid and extensive urbanization in the LC 3 induced increase in mobility. External midshaft and subtrochanteric measurements of at least 152 femora and measurements of 55 tibiae at the nutrient foramen were taken to investigate the differences in the level of terrestrial mobility between four LC 3 and one EBA chronological subsets. Also the correlation was examined between shaft cross-sectional shapes and frequency of linear enamel hypoplasia (LEH) in canines, as a proxy indicator of population stress. Due to post-mortem damage, sex assessment was based only on the size of measured bones. In spite of the limited quality of the gathered data, significant differences in femoral midshaft shape in males were observed between the LC 3 and EBA subsets and the average shape index scores appeared to be correlated with the LEH frequencies. No such result was obtained for females, suggesting that only males were more mobile in the LC 3 and their mobility level was associated with general population stress. In contrast, in females the average shape of

∗ Corresponding author. Tel.: +48 225522837; fax: +48 225522801. E-mail address: [email protected] http://dx.doi.org/10.1016/j.jchb.2014.09.003 0018-442X/© 2014 Elsevier GmbH. All rights reserved.

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subtrochanteric femoral cross-section was more variable between temporal subsets. The patterns of temporal differences in tibial cross-section at the nutrient foramen were not conclusive due to the small sample size. Obtained results suggest that males in the LC 3, the period of rapid urbanization, were more mobile than in the EBA, when the population size was considerably smaller. This mobility may have been related to need of searching for alternative resources for the overpopulated early city. © 2014 Elsevier GmbH. All rights reserved.

Introduction Tell Brak is a major archaeological site in the Khabur drainage, located near Wadi Jaghjagh, some 30 km northeast of the modern town of Hassake, NE Syria (36◦ 40 00 N 41◦ 03 30 E). The main mound covers more than 60 ha and rises to ca. 40 m above the surrounding plain; it contains many strata of occupation from at least the Late Chalcolithic 2 (LC 2, ca. 4200–3900 BCE) to the Late Bronze Age (ca. 1500–1200 BCE). Tell Brak was excavated between 1937 and 1938 by Sir Max Mallowan (Mallowan, 1947) and then since 1976 by David and Joan Oates from Cambridge University, UK, recently under the field direction of Augusta McMahon (Oates et al., 1997, 2001). During the past dozen years, archaeological activities at Tell Brak focused chiefly on the Late Chalcolithic strata excavated in Area TW on the northern slope of the main mound and in Area T2 at a western satellite mound called Tell Temmi (Oates, 2005; Skuldbøl, 2009; Fig. 1). The discovery of large public buildings and a district of workshops has shown that by the beginning of the 4th millennium BCE, the site was a fully grown urban centre, with efficient central administration and advanced craft specialization (Oates et al., 2007). The presence of the so-called Eye Idol Temple, dated to ca. 3800–3600 BCE, suggests that the site was also an important cultic centre at that time (Oates and Oates, 1997). Systematic survey around the site has shown that the settled areas covered ca. 55 ha in the LC 2 and the site grew rapidly to more than 130 ha during the LC 3 (ca. 3900–3600 BCE) (Ur et al., 2007). This was almost twice the size of the Early Bronze Age (EBA) settlement when the site was the capital city of an important kingdom of Nagar, but the size of the settlement was only

Fig. 1. Map showing the location of excavated areas at Tell Brak. Courtesy of Augusta McMahon.

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Fig. 2. Map showing the location of excavated areas at Tell Majnuna. Courtesy of Augusta McMahon.

ca. 70 ha (Ur et al., 2011). This discovery has contested widely accepted models of early urbanization in ancient Mesopotamia. Previous interpretations argue that the first cities emerged ca. 3600 BCE in the southern alluvium of Mesopotamia as power centres administering growing local irrigation networks and that urbanism was much later implemented in the zone of rain-feeding agriculture of Northern Mesopotamia (cf. Algaze, 2008; Ur, 2010). This picture of growing social complexity has been complicated by the accidental discovery of large human and animal bone deposits at Tell Majnuna, another small satellite mound 700 m north of Tell Brak (Fig. 2; McMahon and Oates, 2007). Rescue excavations carried out between 2006 and 2008 revealed that this site was a huge midden dated exclusively to the LC 3 and containing at least two large and five smaller dense clusters of disarticulated or partially articulated human remains. At the top, also a regular cemetery with single pit burials was found (McMahon, 2008). In all, the contexts contained complete skeletons of 53 individuals and commingled remains of at least 175 individuals (minimum number of individuals [MNI] after the number of temporal bones ´ 2009). However, only a small part of the site has been and femora) (Sołtysiak and Chilinska-Drapella, excavated, so the total number must be much higher. In the LC strata at Tell Brak itself, more than 100 human skeletons were found, with most of them representing subadult individuals (Sołtysiak, 2009). The secondary deposits differed in sex and age-at-death profiles, although in all of them bones had been gnawed by carnivorous animals and many other taphonomic effects were observed (Karsgaard ´ and Sołtysiak, 2007; Sołtysiak, 2007, 2008; Sołtysiak and Chilinska-Drapella, 2009). Their absolute chronological spacing is not known, but the stratigraphic positions suggested that the earliest deposit was located in Area MTW, and it preceded by some decades the deposit in Area EM locus 6. Several small bone clusters were found above EM loc. 6, with EM loc. 25 and EMS loc. 6 the most numerous. Finally, the regular cemetery on the top of the site (Area EME) may be a century or two later than the earliest deposits at Tell Majnuna basing on pottery assemblages (McMahon et al., 2011). These four chronological subsets ranging for no more than three centuries are labelled here MTW, EM6, EM25 and TOP, respectively. The sample of human remains from Tell Majnuna is contemporary with the period of maximum settlement size of Tell Brak. No precise estimation of the number of city inhabitants is possible, but if the population density was between 100 and 150 persons/ha (Hassan, 1981), a reasonable minimum estimate of population size is between 13,000 and 20,000 individuals.

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Proper provisioning of such an enormous population must have been difficult and the cultivation of distant fields as well as the transportation of food from remote areas would have presented a major issue for the city dwellers (Sołtysiak, 2010), especially if the lack of donkeys as pack animals in that period is taken into account (Rossel et al., 2008; cf. Vila, 2006). Moreover, Tell Brak is located in the marginal dry farming zone (Ceccarelli et al., 2007), which makes agriculture to some extent unpredictable and subject to high inter-annual variability, in turn potentially increasing the need for mobility in search of alternative resources. It may, therefore, be hypothesized that the level of terrestrial mobility in the LC 3 population of Tell Brak, including the individuals buried at Tell Majnuna, was higher than in periods where the settlement occupied a much smaller area, taking into account the greater average distance to fields and pastures which were necessary to feed a larger population. Several skeletons roughly dated to the later EBA (ca. 2500–2100 BCE) were found at Tell Brak itself (Sołtysiak, 2009), so this hypothesis may be checked by comparison between the LC 3 and EBA samples from the same site. The relatively large number of individuals buried in the various deposits at Tell Majnuna also gives an opportunity to check whether the level of mobility was correlated with the population pressure. Archaeological survey methods offer too low a chronological resolution to observe changes in settlement size within the LC 3, but it is possible to use stress markers (such as linear enamel hypoplasia, LEH) as a proxy for population pressure in the four defined relative chronological subsets, assuming that the larger the population is in relation to its resources, the greater will be the risk of crop failure causing stress in that population. In a secondary deposit of commingled human remains, it was impossible to match long bones with teeth, so only similarity in general temporal trends in bone cross-sectional shape and LEH may be searched for as evidence of relationship between environmental stress and mobility. The cross-sectional geometry of the femur and tibia The most popular method of assessing the level of mobility (defined here as the average daily distance travelled with loads) in past human populations is based on the observation that bone functional adaptation to loads may be reflected in the cross-sectional properties of femoral and tibial shafts (cf. Frost, 2003; Meyer et al., 2011; Shaw and Stock, 2009). There are many studies showing that the robustness and shape of both bones at midshaft significantly differ between more and less physically active living people (Duncan et al., 2002; Heinonen et al., 2002; Macdonald et al., 2009; MacDougall et al., 1992; Shaw and Stock, 2009; Vainionpää et al., 2007) as well as between more mobile and more sedentary past human populations (Holt, 2003; Marchi, 2008; Marchi et al., 2006; Shackelford, 2007; Sparacello and Marchi, 2008; Sparacello et al., 2011; Trinkaus and Ruff, 1999) and that shape is a better indicator of mobility than robustness (Stock, 2006). However, the relationship between mobility and shaft cross-sectional properties is still not completely clear and there are many caveats in interpreting behaviour from bone shape parameters (cf. Ruff et al., 2006). First, the functional adaptability of bone can differ between the modelling (growth) phase in subadults and remodelling phase in adults, the former being characterized by higher potential plasticity (Bass et al., 2002; Frost, 1985; Goldman et al., 2009). This may affect the interpretation of bone geometry in populations where activity patterns of adults and subadults were different, but it may be safely assumed than in pre-industrial populations older children and adolescents were already involved in adult-like work (Pearson and Lieberman, 2004; Ruff, 2000). Thus, in spite of different susceptibility to loadings at different stages of ontogeny, it is still possible to reconstruct the general activity pattern using adult bone cross-sectional properties (Ruff et al., 2006). Another problem is related to some uncertain elements in the model explaining how loadings influence bone shape and robustness. Most authors accept the beam model adopted from engineering and assume that the more the bone area is distant from the cross-sectional centroid, the greater is the bending and torsional rigidity and strength in this direction (Bertram and Swartz, 1991). Strain and stress on bone during locomotion may be analysed in vivo using animal models and several studies have supported the beam model (cf. Robling et al., 2002), although there are also results suggesting that the strain distribution may be different than predicted from bone shape (Demes et al., 2001; Lieberman et al., 2004; Pearson and Lieberman, 2004). Moreover, strain direction may be variable depending on the locomotion mode (e.g., different in stepping and galloping horses) which makes any

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prediction more difficult. Research on animal models has also shown that recurrent short episodes of high loading affect bone shaft geometry more than prolonged but moderate loadings (Frost, 1997, 1999, 2003; Kerr et al., 1996; Milgrom et al., 2000; Robling et al., 2002), although constant moderate strain may also influence bone geometry to some extent (Fritton et al., 2000; McLeod et al., 1998). Human bipedal locomotion is unique and it is uncertain how far studies on animals may be applied to research on human bone shaft geometry. Only very limited in vivo studies on strains in human bone have been undertaken so far (Burr et al., 1996; Peterman et al., 2001), and the computer 3D models still produce unrealistic results (Polgar et al., 2003), so the actual mechanism of functional femoral and tibial shaft adaptation in humans still remains not completely clear (cf. Burr et al., 1996; Milgrom et al., 2000). Obviously, bones cannot be considered in isolation from muscles, as most loadings on bone are induced by muscle activity (Frost, 1997; Lu et al., 1997; Peterman et al., 2001). In lower limbs, the adductors and hamstrings should be considered and these groups of muscles most likely affect bone shape through bending induced at their insertions along the linea aspera at the posterior aspect of the femur and also in the posterior shaft of the tibia (Holt, 2003; Mittlmeier et al., 1994; Morrison, 1970). The positions of these muscular attachments are concordant with the maximum strain, usually oriented in the antero-posterior plane both in walking and in running (Peterman et al., 2001). Femoral and tibial shaft geometry not only reflects terrestrial mobility, but may be influenced also by topography (Ruff, 1999) and by climate (Stock, 2006; Stock and Pfeiffer, 2004), as well as general body proportions (Ruff, 2000; Ruff et al., 2006; Shaw and Stock, 2011; Weaver, 2003), variability in muscle attachment areas (Duda et al., 1996), growth pattern (Shaw and Stock, 2011) and osteogenic hormone secretion (Devlin et al., 2005). Some authors point also to possible general genetic (Ruff et al., 2006) and dietary factors (Stock, 2002). It is then necessary to take into account these variables in studies on mobility in past human populations (Ruff, 2008). The most detailed insight into cross-sectional properties of bone shafts is provided by CT scans (Jungers and Minns, 1979), which are sometimes replaced by less costly external moulds supplemented by bipolar radiographs to estimate the dimensions of the medullary cavity (Ruff, 2002; Shackelford, 2007). External antero-posterior (AP) and mesio-lateral (ML) dimensions are the least precise (Ruff, 2002) but also the easiest to obtain and may be considered as an approximate substitute for CT scans in research on bone shape and robustness (Bridges et al., 2000; Stock and Pfeiffer, 2004; Stock and Shaw, 2007; Wescott, 2006). Among several observed cross-sectional parameters, total area (TA) and bone shape expressed as the ratio of AP to ML (Ix /Iy ) or maximum and minimum second moments of area (Imax /Imin ), may be roughly approximated by the use of standard external measurements, AP and ML diameters at midshaft and in subtrochanteric region of femur as well as maximum and minimum diameters of tibia at the nutrient foramen (Jungers and Minns, 1979; Stock and Shaw, 2007; Wescott, 2006). Fortunately, both diameters are considered most useful in reconstructing behaviour from cross-sectional geometry (Demes, 2007; Lovejoy et al., 1976; Ruff, 2008). Mobility in the LC 3 and EBA populations of Tell Brak The ancient inhabitants of Tell Brak were agriculturalists operating in the marginal area of the dry farming zone called the Fertile Crescent by modern scholars. Both in the LC and in the EBA, the main crops were wheat and barley, although the proportions of these two cereals may have, to some extent, varied in certain periods. Also some legumes were planted, primarily lentils (Charles and Bogaard, 2001; Hald, 2008; Hald and Charles, 2007). Plant-derived food was supplemented by dairy products and meat from domesticated animals, chiefly caprines, followed by cattle, and occasionally pigs. Hunting and fishing, if practised at all, were marginal in both periods (Clutton-Brock et al., 2001; Dobney et al., 2003; Weber, 2007). It may then be assumed that there is no difference in the subsistence strategy between the two compared periods, except some possible improvements in agricultural technology, such as the introduction of the plough with seeder in the later 4th millennium BCE (Moorey, 1994). The topography of the neighbourhood of Tell Brak did not change substantially through the 4th and 3rd millennia BCE, although the central mound gradually grew in that time. However, there is one factor which could have affected the level of human mobility: the introduction of the donkey as a pack animal in the later 4th millennium BCE (Greenfield et al., 2012; Rossel et al., 2008; Vila, 2006).

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Due to the lack of navigable rivers in the area, the LC population must have relied on human porters, while the EBA people used not only donkeys, but also more efficient kunga, hybrids of donkey and wild onagers, which were witnessed by contemporary texts as the famous breed of Tell Brak and attested also in the archaeological record (Oates et al., 2008). In both periods, a fraction of local population was involved in activities other than agriculture, such as crafts, administration, etc. It is not possible to estimate the proportion of city dwellers who were not farmers, and it may be only speculated that they were more frequent in the EBA when transportation of food from more distant places may have provided the capital city of the kingdom with proper alimentation. Moreover, Tell Brak during that time was surrounded by several relatively large villages which could be the place of residence of farmers. On the other hand, Tell Brak in the LC 3 was surrounded by several square kilometres of space with virtually no villages and also far distant trade of food was unrealistic, so it is likely that more farmers resided in the city itself (Ur et al., 2011; Wright et al., 2006–2007). All factors discussed above are, however, related chiefly to the size of the settlement, which in the EBA was approximately half of that in the LC 3 (Ur et al., 2007, 2011). This implied also a difference in the area required for feeding the local population. This change in the reach of the exploited terrain should affect the level of terrestrial mobility, which can be expected to be considerably lower in the EBA population. The model Several authors have observed a gradual increase with time in femoral midshaft circularity and a decrease in robustness, especially in the Upper Palaeolithic, but in many cases also in times of transition from hunting and gathering to agriculture (Holt, 2003; Maggiano et al., 2008; Ruff, 1987; Shackelford, 2007; Sparacello and Marchi, 2008). A greater sexual dimorphism in the cross-sectional characters in foragers compared to that of farmers was interpreted as a reflection of high mobility in male hunters contrasted with the more stationary activities of female gatherers, as opposed to the sedentary life of both sexes after the adoption of agriculture (Ruff, 1987, 2000, 2008). In the specific case of Tell Brak, both compared chronological subsets represent farmers and the difference between them should be related to population size and transportation means and not to the subsistence strategy. Some textual and iconographical evidence from Mesopotamia show that both males and females may have acted as porters (Molleson and Hodgson, 2000), so there should be a difference in mobility between the LC 3 and EBA chronological subsets, but no evident sexual dimorphism in bone shape in either period is expected. If a population approaches the maximum carrying capacity in a local ecosystem, and therefore is more subject to environmental stress (also due to higher risk of infectious diseases in overcrowded place), simultaneously the search for alternative resources can increase mobility. As a result, a correlation may be expected at the population level between the frequency of skeletal stress markers and the cross-sectional characteristics of femora and tibiae. In the present study, the average shaft shapes will be compared with the mean incidence of linear enamel hypoplasia, which is considered to be a reliable non-specific stress marker (Hillson, 1996; Wright and Yoder, 2003). There are therefore three predictions which will be tested in the present paper: (1) the level of terrestrial mobility as measured by the cross-sectional shape of femoral and tibial shafts should be significantly greater in the LC 3 than in the EBA; (2) this difference should be related to agricultural activities, which are less attributable to a specific sex than are hunting and gathering, so it is expected to be observed both in males and in females; (3) the variability in terrestrial mobility among the LC 3 chronological subsets may have been related to more strenuous agricultural activity in distant or worse quality fields and to the search for alternative resources during episodes of overpopulation; in that case, the coincidence between mobility and the level of environmental stress may be expected. Material and methods Human remains are usually not well preserved in the arid areas of the Near East, chiefly due to the marked annual variation in temperature and humidity (Bollongino and Vigne, 2008). Most skeletons from Tell Brak dated to the EBA were buried in simple pit graves in a domestic context, while a few were found in secondary multiple burials (Sołtysiak, 2009). Most epiphyses of long bones were absent

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or highly fragmented and the sex and age-at-death assessment were problematic in most cases due to the poor recovery rate of pelves and skulls. For that reason, mainly long bone shafts were available for study. The state of preservation of skeletons in the LC 3 multiple deposits at Tell Majnuna was considerably better, but also in that case long bones often lacked epiphyses due to gnawing by animals ´ 2009). Only in a few cases was it possible to (Sołtysiak, 2008, 2010; Sołtysiak and Chilinska-Drapella, fit pelves with lower limb long bones, so again it was usually not possible to assess sex and age-atdeath using pelvic morphology. Skeletons in the cemetery at the top of the site were complete and articulated, but the short distance to the surface made them more vulnerable to erosion of trabecular bone. Only a few adult skeletons dated to the LC 3 were found at Tell Brak itself and at Tell Temmi, all of the skeletons were even more fragmented than the EBA skeletons (Sołtysiak, 2009). The EBA and LC 3 samples are not homogenous nor representative of the local population, and age and sex bias is evident especially in some deposits at Tell Majnuna, e.g. with more older children and more females in EM6 than elsewhere and with more males in MTW (McMahon et al., 2011). However, the archaeological context suggests that all or most individuals belonged to the lower social classes and no elite graves have been found so far at Tell Brak, so in spite of all the differences and biases, the samples still may be used to estimate the level of terrestrial mobility. Also the EBA skeletons were found chiefly in pit graves or secondary deposits without rich grave goods. All the human remains from Tell Brak and its satellite mounds were studied in the dig house at Tell Brak during the autumn survey seasons 2004–2006 and spring excavation seasons 2007–2009. It was not possible to transport them outside of Syria and the fieldwork time was short, so no CT scans nor moulds were taken and only the external shaft diameters have been measured. Measurements and their interpretation Only bones with no evident erosion of shafts were selected for the analysis. Femoral shafts were measured in the subtrochanteric region, 30–40 mm below the lesser trochanter at the most lateral expansion of the shaft (Buikstra and Ubelaker, 1994, measurements 64 and 65; Martin and Saller, 1957, measurements M10 and M9), and at the approximate midshaft where the linea aspera exhibited greatest development (Buikstra and Ubelaker, 1994, measurements 66 and 67; Martin and Saller, 1957, measurements M6 and M7). Fragmentary shafts (usually with epiphyses gnawed out) were oriented to anatomical planes using the position of the linea aspera. Tibial shafts were measured at the level of the nutrient foramen (Buikstra and Ubelaker, 1994, measurements 72 and 73; Martin and Saller, 1957, measurements M8a and M9a). All measurements were taken with a sliding caliper, to the nearest 0.5 mm. Due to time constraints during the fieldwork, it was not possible to repeat measurements and estimate the intraobserver error. Both right and left bones from secondary commingled deposits were measured, as there is no significant directional asymmetry in the lower limbs (Auerbach and Ruff, 2004). In articulated skeletons, only the better preserved side was selected. Most bones were separated and, as only a small part of the site was excavated, it may be assumed that the contralateral counterparts of most bones were not retrieved. For that reason, the statistical analyses were done for all single right and left bones except those for which likely counterparts were identified. The criteria for identifying probable counterparts (separately for each deposit) were: (1) a difference in antero-posterior and mesio-lateral diameters of 1 mm or less; (2) morphological similarity, especially in expression of the linea aspera, gluteal tuberosity and lateral fossa; (3) and a similar degree of degenerative joint disease, if observed. If two bones were identified as probably belonging to the same individual, the less complete one was rejected. If both were complete, the left one was selected for further analysis. In total, when such procedure was applied, 152 femoral midshaft measurements, 106 femoral subtrochanteric measurements and 55 tibial measurements were used in the present study. For the femora, antero-posterior and mesio-lateral measurements were taken, and may be used as measures of variations from circularity analogous to AP and ML second moments of area (Ix and Iy ) (Jungers and Minns, 1979). In tibiae, maximum and minimum diameters were measured, because, due to the high fragmentation rate, it was not possible to fix the proper anatomical position of the bone. These measurements correspond to maximum and minimum second moment of area (Imax and Imin ) (Macdonald et al., 2009). Only adult bones were measured, where epiphyses were completely fused. If no epiphysis could be observed due to post-mortem damage, the roughness of

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the linea aspera in the femora and the popliteal line in the tibiae were used as indicators of adult ageat-death (Scheuer and Black, 2000; see also Galtés et al., 2006). Individuals with smooth linea aspera were not taken into account, even if some of them might be females and not sub-adults. For each of the three measured cross-sections, the shape indices were calculated using AP and ML diameters for the femur and minimum and maximum diameters at the nutrient foramen for the tibia. Femoral midshaft shape was estimated using the AP/ML ratio, while subtrochanteric shape was estimated using ML/AP ratio. In all three cases, the size index was calculated as ML+AP (Wescott, 2006). The last variable is expected to be correlated with body size and—in consequence—with sex, so without reliable sex assessment and with no possibility to control for body size by using such measurements as femoral head diameter or bi-iliac breadth (Ruff, 1995; Shaw and Stock, 2009; Wescott, 2006), the size index in the present study may be used only for a rough sex discrimination. To make the dataset uniform, no other sex assessment methods were applied, even if they were available for complete skeletons retrieved from the regular cemetery at the top of Tell Majnuna and from various locations at Tell Brak. Otherwise, the shape indices are size-independent (Pearson et al., 2006) and may be interpreted as proxy indicators of terrestrial mobility, assuming that the higher the loads subject to bending strain, the greater deviation from circularity (Duncan et al., 2002; Shaw and Stock, 2009). Taking into account the morphology of femora and tibiae and the location of major muscle insertions, the higher level of mobility should especially increase AP/ML indices in femoral midshaft and proximal tibia (Burr et al., 1996). Linear enamel hypoplasia (LEH) was chosen as the non-specific stress marker correlated with the general health and nutritional status in a population (Hillson, 1996) and its frequency should increase with a fall of available resources per capita, thus reflecting an increase in the population size or a decrease in the carrying capacity limits. The incidence of LEH in defined chronological subsets was observed on upper canines, which are more susceptible to this condition than other teeth (Hillson, 1996). For the present study, the frequency of crania with at least one palpable hypoplastic line in at least one upper canine was calculated (Schultz, 1988). Although the frequency of LEH may differ between sexes, no reliable sex assessment was possible in most crania found at Tell Majnuna, so only the general LEH frequencies for whole subsets were counted.

Statistical analysis Any sex assessment using the pelvis or skull was possible in less than half the articulated skeletons and in none of the disarticulated bones which dominated in the LC 3 subsets. For that reason, the analysis of the degree of sexual dimorphism was possible only in an indirect way. The whole sample was divided into two subsamples including small (ML+AP of a given bone cross-section below the average) and large individuals (ML+AP above the average) and the differences between these subsamples were interpreted as approximate estimates of the differences between sexes. For femoral midshaft, the division between small and large bones was set at 54.75 mm, for femoral subtrochanteric region at 57.75 mm and for proximal tibia at 55.75 mm. These values were similar to average differences between males and females in a reference sample of human remains from various North Mesopotamian sites with available sex assessment based on pubic morphology (Sołtysiak, 2010: Table 22). Femoral and tibial cross-sectional size is a relatively good indicator of sex in North Mesopotamian populations, with discriminant effectiveness of 80–85% (Sołtysiak, 2010: Table 22), so it may be assumed that the subsample of small bones included less than 20% males and the subsample of large bones included more than 80% males. Although there was some evident bias towards males or females in some assemblages of human bones at Tell Majnuna, the overall sex ratio in all combined contexts was close to 1:1 (Sołtysiak, 2010). After checking the normality of all distributions, the differences between chronological subsets for small and large bones and the differences between small and large subsamples in a given subset were tested with the one-way ANOVA and LSD as post-hoc tests, as well as the Student’s t-test. In the case of the tibiae, the sample size was relatively small, and only the general difference between the LC 3 and EBA subsets was checked. Spearman rank correlation coefficients were calculated for the frequency of linear enamel hypoplasia and for both femoral shape indices. All statistics were calculated using Statistica, version 9.0 (StatSoft Inc., 2010).

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Results Neither shape nor size indices differ significantly from a normal distribution, as assessed using the Kolmogorov–Smirnov test (all p > 0.20). Shape indices are expected to conform to a log-normal distribution, but actually the deviation from a normal distribution is small and does not affect parametric tests in any of the three cases, so for the sake of clarity they were not log-transformed in the present analysis (Table 1). Measured bones were divided into two subsamples, separately for each of the three cross-sectional areas, using mean size indices. Assuming an equal distribution of sexes in the whole sample, the subsample of small bones (AP+ML below the mean) is expected to contain more than 80% bones belonging to female individuals and the subsample of large bones (AP+ML above the mean) is expected to represent more than 80% male skeletal elements. The subsamples of small and large bones are thus used as proxies for females and males respectively. The results of the one-way ANOVA and t-test for the small and large bone subsamples are presented in Tables 2–4. Differences in tibiae between LC 3 and EBA subsets are not statistically significant, which can be expected taking into account the small sample sizes in the compared subsets. The shape of the subtrochanteric region is relatively stable across all subsets for the large bones and variable for the small bones, with the most significant difference between the EM6 and EBA subsets. In contrast, the shape of the femoral midshaft is stable for the small bones and variable for the large bones, with the most significant difference between the MTW and EBA subsets. In spite of the small sample size in some cases, all three early chronological subsets (including bones from the secondary deposits at Tell Majnuna) exhibit significant differences in the femoral midshaft shape between the small and large bones (Table 2, Fig. 3a). In most subsets, the variance is higher for the large bones, but only in the most numerous MTW subset is the difference in variance between the large and small bones statistically significant (F = 2.19, p < 0.05). For the large bones, the comparison of the average femoral midhaft shape index and the frequency of linear enamel hypoplasia exhibited a significant Spearman rank correlation (rs = 0.90, p < 0.05, see Fig. 4). For the small bones, no such effect was observed (rs = 0.32, NS). The LEH frequencies differ significantly among the five chronological subsets, with 2 = 11.1, p < 0.03. The variability pattern for the subtrochanteric femur differs from that observed for the femoral Table 1 Basic statistics for size and shape indices in the whole sample from Tell Brak and Tell Majnuna. Cross-section

n

Size (AP+ML)

Femur, subtrochanteric region 106 Femur, midshaft 152 Tibia at the nutrient foramen 55

Shape (AP/ML or ML/AP)

Min. Max. Mean SD

Sk

Ku

Min. Max. Mean SD

Sk

Ku

47.5 44.5 47.0

0.12 0.02 0.09

0.02 -0.32 -0.27

1.11 0.85 1.33

-0.09 0.74 0.69

-0.02 0.63 0.35

70.0 68.0 66.0

57.8 54.7 55.6

4.42 4.70 4.33

1.64 1.49 2.03

1.35 1.07 1.60

0.10 0.12 0.15

SD, standard deviation; Sk, skewness; Ku, kurtosis. Table 2 Differences in femoral midshaft shape index between chronological subsets, separately for large and small bone subsamples. Chronological subset

Large

Small

n

Mean

SD

n

Mean

SD

MTW EM6 EM25 TOP LC3—Tell Brak EBA

30 14 12 10 2 7

1.11 1.13 1.19 1.07 1.16 1.02

0.13 0.08 0.15 0.13 0.21 0.06

28 25 4 5 3 12

1.01 1.03 1.03 1.02 1.01 1.03

0.09 0.09 0.08 0.07 0.04 0.11

ANOVA results

F = 1.98, p < 0.10 LSD: MTW vs TOP, p < 0.05 LSD: MTW vs EBA, p < 0.01

F = 0.20, NS

Percent frequencies of linear enamel hypoplasia in chronological subsets.

t

p

3.65 3.47 1.99 0.83 1.37 −0.19

<0.001 <0.002 <0.07 NS NS NS

Hypoplasia n 35 26 12 19 – 9

% 43 73 83 58 – 33

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Table 3 Differences in femoral subtrochanteric shape index between chronological subsets, separately for large and small bone subsamples. Chronological subset

MTW EM6 EM25 TOP LC3—Tell Brak EBA

Small

Large n

Mean

SD

21 8 8 7 3 7

1.35 1.32 1.36 1.38 1.42 1.33

0.12 0.07 0.09 0.07 0.10 0.09

ANOVA results

F = 0.56, NS

n 17 14 5 4 1 7

t Mean

SD

1.32 1.41 1.32 1.39 1.28 1.29

0.09 0.08 0.12 0.09 – 0.09

−0.81 2.34 0.54 −0.30 – 0.78

p

NS 0.03 NS NS – NS

F = 2.48, p < 0.05 LSD: EM6 vs EM25, p < 0.02 LSD: EM6 vs EBA, p < 0.01

Table 4 Differences in tibial shape index between chronological subsets, separately for large and small bone subsamples. Chronological subset

MTW EM6 EM25 TOP LC3—Tell Brak LC3—all subsets EBA LC3 vs EBA

Large

Small

n

Mean

SD

11 3 4 1 1 20 5

1.60 1.57 1.65 1.55 1.81 1.61 1.48

0.18 0.13 0.15 – – 0.16 0.09

t = 1.77, p < 0.10

n 8 7 3 4 1 23 7

Mean

SD

1.60 1.61 1.54 1.74 1.35 1.61 1.59

0.16 0.08 0.04 0.21 – 0.15 0.15

t

p

−0.01 −0.57 1.23 – – 0.11 −1.37

NS NS NS – – NS NS

t = 0.35, NS

midshaft. In this case, a significant difference between the large and small bone subsamples occurs only in the EM6 subset and a higher variability among subsets is observed for the small bones (Table 3, Fig. 3b). No significant correlation between the subtrochanteric shape index and the LEH frequency was observed either in the small or the large bone subsamples. The individual correlation between the femoral subtrochanteric and the midshaft shape indices is negative and statistically significant (Pearson’s r = −0.48, p < 0.005, n = 73). For tibiae at the nutrient foramen—just like for the femoral midshaft—the difference between the LC 3 and EBA samples is greater for the large bones than for the small bones, but the sample size is very small and the t-test value for the large bones is not significant at the 0.05 level (Table 4). Discussion In spite of all the methodological problems related to the salvage character of the project and to the lack of reliable sex assessments and body mass estimates, some interesting patterns of crosssectional shape variability have been observed in the sample of femora and tibiae from Tell Brak and Tell Majnuna. Of course, they must be regarded as preliminary findings, as the statistical significance of some differences should not be overestimated in such a biased dataset. Differences in mobility between the LC 3 and EBA Previous studies have shown the association between the level of terrestrial mobility and the midshaft shape of femur and tibia. Thus, if the LC 3 population of Tell Brak was more mobile than the EBA inhabitants of the site—as predicted from the settlement size, available technology and presence or absence of pack animals—higher average values of femoral midshaft and tibial shape indices should be observed in the earlier chronological subsets. This prediction has been partially

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1.20

AP/ML index at midshaft

1.18 1.16 1.14 1.12 1.10 L

1.08

S

1.06 1.04 1.02 1.00 MTW

EM6

EM25

TOP

EBA

Chronology

ML/AP subtrochanteric index

1.42 1.40 1.38 1.36 L

1.34

S 1.32 1.30 1.28 MTW

EM6

EM25

TOP

EBA

Chronology Fig. 3. Differences in average femoral shape indices between the five chronological subsets, separately for large (L) and small (S) bones.

confirmed in the present study, although only the femoral midshaft shape in the large bone subsample differed significantly between the LC 3 and EBA chronological subsets, and the index of tibial shape at the nutrient foramen in the large bone subsample—much less numerous than the number of measured femoral midshafts—is close to the conventional significance level. On the other hand, there is no such difference in the small bone subsample and in particular the femoral midshaft shape seems to be surprisingly constant through all the examined chronological subsets. Moreover, in all LC 3 chronological subsets, the level of sexual dimorphism, measured as the average difference between small and large bone subsamples, is high and statistically significant in all three deposits of commingled human remains, yet very low in the EBA chronological subset. If then, the first prediction about the difference in mobility between the LC 3 and EBA subsets seems to be confirmed at least by the pattern of femoral midshaft shapes, the second prediction about the equal mobility levels of males and females in the agricultural population appears to be false. The temporal trend in the sexual dimorphism of femoral midshaft shape, although assessed through

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proxies, resembles the pattern observed in studies on foragers and on transition from hunting to agriculture, where the increase in cross-sectional circularity was parallel to the decrease in sexual dimorphism of the femoral midshaft shape. The obtained results are, to some degree, similar also to the pattern of sexual dimorphism observed in Early Medieval populations of Western Europe (Pomeroy and Zakrzewski, 2009). It seems then likely that mostly males in both compared periods were involved in agricultural activities affecting terrestrial mobility, while the mobility of females was not influenced by the need to operate in more or less distant arable fields or to gather alternative food items. It is also likely that household activities attributed to females remained constant from LC 3 to EBA and the loads of males were at least partially reduced by the use of pack animals. Analogous difference between sexes has been found also in Maya Indians, another agricultural population lacking any transportation means other than human porters (Wanner et al., 2007). The correlation of the femoral subtrochanteric shape with terrestrial mobility has not been studied frequently and this cross-sectional area seems to be a worse predictor of mobility than the midshaft femur (Wescott, 2005). It may be related chiefly to a much more complicated pattern of strains induced by the muscles attached to the proximal femur (Polgar et al., 2003: Fig. 2). In the present study, however, the subtrochanteric shape index is also higher, on average, in the LC 3 than in the EBA subset, although only the difference between the EM6 and EBA in the small bone subsample is statistically significant. Stress and mobility Among the three studied cross-sectional areas, a clear correlation between the cross-sectional shape and the level of environmental stress measured by the frequency of LEH in upper canines may be observed in the femoral midshaft in the large bone subsample (Fig. 4). This is also the cross-sectional trait which is thought to be a reliable predictor of terrestrial mobility and which most effectively differentiates between the LC 3 and EBA chronological subsets in the large bone subsample. Such a correlation was expected between the cross-sectional shape, influenced by the level of mobility and the frequency of LEH, the latter possibly reflecting the relationship between the population size and the carrying capacity level. However, the low quality of available data enables only a very cautious interpretation of the obtained results. First of all, the chronology of human bone deposits at Tell Majnuna is based only on relative stratigraphy and—taking into account the variability in the degree of disarticulation—later secondary deposits of completely disarticulated elements, such as EM6, may have contained bones from primary contexts which predated the MTW 1.5

Standardized AP/ML index & LEH frequency

FMS LEH

1.0 0.5 0.0 -0.5 -1.0 -1.5 MTW

EM6

EM25

TOP

EBA

Chronology Fig. 4. Standardized average femoral midshaft shape index (FMS) in the large bone subsample versus standardized LEH frequency in the five chronological subsets.

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deposits with some articulations preserved, even if the latter were found in earlier strata. Of course, it would not affect the overall correlation, but only the temporal trend shown in Fig. 4. The second problem is the heterogeneity of all the temporal subsets and the differences in sex and age-at-death profiles observed at Tell Majnuna. In MTW, males were more frequent, while EM6 contained more ´ 2009 for details). The subset remains of females and subadults (see Sołtysiak and Chilinska-Drapella, EM25 included human remains from several smaller clusters dispersed in many strata preceding the cemetery on top and later than EM6. This heterogeneity may affect results in many unpredictable ways. However, bearing in mind all these caveats, the overall pattern may be cautiously interpreted as evidence of the gradual relative overpopulation and increased terrestrial mobility during the formation of the midden at Tell Majnuna and then some degree of relaxation towards the end of the LC 3, when the top of the midden was used as a regular cemetery. However, in this period, in general, the levels of mobility and environmental stress were greater than in the EBA. Even if the evidence is not very strong, the results enable some insights into the living conditions in a rapidly growing early urban centre and suggest that the process of urbanization reduced the quality of life of inhabitants of Tell Brak, at least of those who were finally buried at Tell Majnuna. The results of the present research are consistent with botanical evidence which shows higher reliance on barley which is more stress resistant than wheat and exploitation of secondary resources such as grass pea (Hald, 2008). Two patterns of functional adaptation in femur One of intriguing results of the present research is the difference in patterns of femoral midshaft and subtrochanteric shape indices. For femoral midshafts, the average shape is similar in all chronological subsets for the small bones, but significantly variable for the large bones, while the femoral subtrochanteric region exhibits higher variability in the sample of all chronological subsets for the small bones (Fig. 3). This difference is paralleled by significant although moderate individual correlation between these shape indices. Three possible factors may underlie this difference in patterns: the anatomy of the pelvic girdle, sex-specific growth trajectories or gender-specific physical activities. Sexual dimorphism in the morphology of the pelvic girdle is related to the compromise between bipedality and gestation in females (Arsuaga and Carretero, 1994). Although most marked in the area of the pubic symphysis, it affects the whole os coxae and also the proximal femur which follows the position of the acetabulum. Differences in the pelvic shape are also paralleled by the difference in ligament and muscle position and activity, and especially the gluteal muscles exhibit some inter-sex difference (Hart et al., 2007; Zazulak et al., 2005). Thus, the different patterns in the cross-sectional shape of the subtrochanteric region between males and females may be to some extent related to the overall difference in the pelvic girdle anatomy. In contrast, the femoral midshaft should be less affected by this factor (Ruff, 2008). Another possible factor is the difference in growth trajectories between males and females (Devlin et al., 2005). Females enter the pubertal growth spurt earlier and the period of accelerated growth is relatively shorter than in males (Bogin, 1999). In effect, the time when femoral shape may be most easily modelled according to the quantity and quality of physical activity (including terrestrial mobility) is earlier and shorter in females than in males. Also the pattern of periosteal and endocortical bone formation differs between the sexes (Bass, 2003). Moreover, the shape of the subtrochanteric region in the femur changes quickly in earlier childhood, but stabilizes after the 5th year of life (Wescott, 2006a), while the linea aspera develops until the completion of femoral growth and even later (Scheuer and Black, 2000). The variability between the temporal subsets in the shape of subtrochanteric region in females may then correspond to different mobility patterns in childhood as opposed to the adult patterns of mobility reflected by the femoral midshaft shape. Last but not least, the difference in patterns of femoral midshaft and subtrochanteric shape indices may reflect gender-specific physical activities which involve loads from hips to femur (Bridges et al., 2000). Little is known about the social organisation of the LC 3 city at Tell Brak, but the analogies from other Mespotamian sites may suggest that there were specific activities attributed to females, such as cereal grinding and food preparation in general (Englund, 1991; Molleson, 1994). They are more stationary than typical male activities such as herding or warfare, and possibly they involved more variable use of the glutei and other muscles attaching to the proximal femur. It is likely that

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these observed patterns are affected by many factors and, in particular, the forces shaping the subtrochanteric region seem to be complex. The limited data discussed in the present paper do not permit a more reliable explanation and more in vivo research is necessary to reveal the causes of the differences between subtrochanteric and midshaft shape variabilities. However, it already seems quite clear that the subtrochanteric shape is not related to terrestrial mobility in such a straightforward way as is the femoral midshaft shape (Ruff, 2008; Wescott, 2005). General discussion The present study, although based on incomplete and biased data, produced some positive results. Femoral midshaft shape in large individuals (i.e. males), as expected, appeared to be a better indicator of terrestrial mobility than femoral subtrochanteric shape, revealing the expected significant differences between the LC 3 and EBA chronological subsets, as well as reflecting the pattern of population pressure assessed by the frequency of linear enamel hypoplasia. The shape of the tibia at the nutrient foramen seems to follow a similar pattern to the femoral midshaft shape, but the small sample size in this case makes the temporal differences statistically insignificant. The most striking result was the high degree of sexual dimorphism in femoral subtrochanteric and midshaft shapes in the LC 3 temporal subsample, which was not expected in a sedentary agricultural population. 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