Late Stone Age subsistence in the Tilemsi Valley, Mali: Stable isotope analysis of human and animal remains from the site of Karkarichinkat Nord (KN05) and Karkarichinkat Sud (KS05)

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Journal of Anthropological Archaeology 27 (2008) 82–92 www.elsevier.com/locate/jaa

Late Stone Age subsistence in the Tilemsi Valley, Mali: Stable isotope analysis of human and animal remains from the site of Karkarichinkat Nord (KN05) and Karkarichinkat Sud (KS05) Brian Finucane

a,*

, Kate Manning b, Mouktarde Toure´

c

a

c

Yale University, 730 Whitney Avenue, Apt. 3a, New Haven, CT 06511, USA b Institute of Archaeology, Oxford University, United Kingdom Direction Regionale de la Jeunesse des Sports, Arts et Culture, Region de Gao, Republique du Mali Received 11 August 2007; revision received 10 October 2007 Available online 3 December 2007

Abstract The pathways leading to the adoption of cereal cultivation and pastoralism in West Africa are poorly understood. In order to elucidate the transition to food production during the Late Stone Age in Mali’s Tilemsi Valley samples of ancient and modern human and animal remains were selected for carbon and oxygen isotope analysis. Our results indicate the inhabitants of Karkarichinkat Nord (KN05) consumed considerable quantities (85%) of carbon derived from C4 plants, either directly in the form of C4 grasses such as wild Panicum sp. and possibly domestic Pennisetum sp. or indirectly through the consumption of C4 grazers such as Bos sp. and Ovis sp.  2007 Elsevier Inc. All rights reserved. Keywords: Bioarchaeology; Stable isotopes; Agriculture; Pastoralism; Neolithic; Sahara; Millet; Cattle

Introduction The transition to food production represents one of the most significant economic shifts in human prehistory. Although we are able to discern the broad outlines of this process in some of the primary centers of domestication such as the Fertile Crescent, China, Mexico, and the Central Andes, less is known about the adoption of agriculture and pastoralism in secondary centers such as sub-Saharan West Africa. Both the absolute and relative timing of the transition to sedentism, the adoption of animal husbandry and the transition to cereal cultivation in this region remain poorly understood (but see Haour, 2003 for a review of the Neolithic in Niger). In order to elucidate the transition to food production at the Late Stone Age (LSA) site of Karkarichinkat Nord (KN05) in Mali’s Tilemsi Valley, stable isotope analysis of archaeological human and animal *

Corresponding author. E-mail address: brian.fi[email protected] (B. Finucane).

0278-4165/$ - see front matter  2007 Elsevier Inc. All rights reserved. doi:10.1016/j.jaa.2007.10.001

remains from the site was undertaken. Whereas analysis of archaeological faunal and floral remains provides a measure of the presence of resources, analysis of the stable isotope composition of an animal’s tissue can provide a measure of the prevalence of these resources in an animal’s diet. Although there have been a number of studies of australopith and early Homo dietary ecology utilizing biogeochemical techniques (see Lee-Thorp and Sponheimer, 2006 for a review), our research represents the first application of stable isotope analysis to the investigation of the diet of prehistoric Homo sapiens in West Africa. Environmental context The Lower Tilemsi Valley is one of several palaeochannels extending north from the Niger River. Although current conditions are principally Saharan, the valley did at one time host an extensive river and tributary network, stretching from the Tanezrouft in the north, to the Niger in the south.

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In the last 30 years, extensive research has been undertaken into the climatic and floral history of the Sahara, demonstrating a distinct humid phase in Africa’s later prehistory, beginning around 12,000 BP (Maley, 1977, 1980, 1982; Le´zine and Cassanova, 1989; Le´zine, 1991; Marchant and Hooghiemstra, 2004; Hillaire-Marcel et al., 1983; PetitMaire and Riser, 1981). Several optimal episodes occurred during this period, notably between 9400 and 7700 BP, and again from 7200 to 4500 BP. During the second of these humid phases, conditions were significantly more erratic, with periods of aridity at 6400 and 5500 BP. Between 5000 and 4000 BP, conditions rapidly deteriorated, with a distinct dry episode around 4200/4000 BP, marking the end of the Holocene humid phase and the onset of current arid conditions. Today, the Tilemsi Valley is a semi-arid grassland which supports a few scattered acacia trees but where annual rainfall is below the minimum required for dry agriculture. However, archaeological and palaeobotanical evidence indicates that conditions during the later Holocene were more comparable to those of the Middle Niger today, where dry agriculture reaches its northern extent, and irrigated croplands are prevalent. The initial palaeobotanical analysis from KN05, undertaken by Dr. Ruth Pelling, has identified fragments of Vitex sp., Panicum sp., Zizyphys sp., and several indeterminate fragments of Leguminosae. These species are more representative of a Sahelian or Sudano-Sahelian environment than of a Saharan one. The faunal remains from KN include aquatic mammals, deep and shallow water fish species, domestic livestock, and wild bovids. The remains of Lates niloticus measuring 1 m, recovered at KN05 attest to the fact that the Tilemsi contained a permanent deep water channel. Today, this sort of mixed faunal assemblages is only found south of the Middle Niger. The origins and development of agriculture and pastoralism in sub-Saharan West Africa Evidence at the site of Nabta Playa E-75-6 indicates domestic cattle were present in the eastern Sahara by 8000 BP. From here, domestic cattle appear to have spread westwards, across the Sahara, and southwards, along the Nile valley. Cattle are present at Gabrong and Baradigiue´ in the Tibesti where remains have been dated to 7455 ± 180 BP (Gautier, 1984; Barich, 1987), and at Adrar Bous in the Te´ne´re desert of Niger, where they have been dated to 6000 BP. After 4000 BP, the deterioration of conditions in the Sahara, prompted the movement of cattle into sub-Saharan West Africa (Clark, 1976; Munson, 1976, 1980; Casey, 1998). Shaw (1977) notes that any movement of pastoral populations prior to this time would have been restricted by the disease vectors of Sahelian West Africa and was only alleviated by a southward displacement of the tsetse barrier 3700 BP. The earliest evidence for agriculture in West Africa appears much later than that for pastoralism. The earliest

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direct evidence comes from the Sahara–Sahel margins. At Karkarichinkat, de Wet (Smith, 1984, p. 89; Smith, 1992, p. 74) identified domesticated pearl millet (Pennisetum glaucum) impressions on pottery, which Smith stylistically dates to the end of the 3rd millennium BP. At Dhar Tichitt, in southwestern Mauritania, impressions of domesticated pearl millet have been firmly dated to at least 3800 BP (Amblard, 1984, 1995; Amblard and Perne`s, 1989). More recently domesticated millet grains have been dated to 3490 ± 50 BP (1878–1744 cal BC) at Birimi in northern Ghana (D’Andrea et al., 2005). Based on the distribution of its wild progenitors, Harlan (1971, 1992) locates the center of millet domestication in the Western Sahara. However, the earliest remains of domesticated millet have been found in western India. At the sites of Koethe, Gujarat, Babor Kot, and Surkotada domesticated millet has been dated to the end of the 5th millennium BP (Tostain, 1998; Fuller, 2003). The archaeologically evidence for the center of millet domestication therefore still awaits discovery in the vast unstudied areas of Western Sahara.

Archaeological context The sites of Karkarichinkat Nord (KN05) and Sud (KS05) are located 80–85 km north of Gao, in Eastern Mali (Fig. 1). They were first recorded by Mauny (1952) who visited the lower Tilemsi Valley in 1952. Two decades later Andrew Smith excavated five test pits, which yielded evidence of an agro-pastoral economy dating to the end of the 5th millennium BP (1974a,b, 2005). At KN05 Smith uncovered evidence for intensive occupation, including pottery, domestic livestock, and fish. Smith also identified domesticated pearl millet (P. glaucum) impressions on ceramics, which he associates with the earliest levels of occupation. However, these samples appear to have been collected only from the surface. They do not provide conclusive support for the notion that a fully developed agricultural economy existed during the site’s initial occupation, nor do these impressions establish the prevalence of millet in the diet of the site’s inhabitants. Although Gaussen and Gaussen (1988) undertook an extensive surface survey and described three broadly contemporaneous cultural facies, their results lack chronological resolution. In order to expand upon Smith’s preliminary findings in 2005 a team from the University of Oxford, working in collaboration with the Direction National du Patrimoine Culturelle, began excavations at KN05. A total of eight 2 · 2 m trenches were excavated, of which three reached basal deposits at 2.40 m. An additional eight trenches were located over eroding human burials (Fig. 2). A series of 10 AMS dates were obtained from the main excavation area, dating the occupation of the site to between 2206 and 2620 cal BC (Table 1). A further AMS date of 2479– 2292 cal BC (OxA-16976) was obtained from trench 4, on a piece of charcoal directly below skeleton 1, indicating

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Fig. 1. Map of Mali indicating location of Karkarichinkat Nord and Sud.

the main phase of occupation and the eroding surface skeletons were contemporaneous (Fig. 3). Domestic livestock, notably cattle, as well as sheep, goat, and fish were found in abundance throughout the sequence. However despite intensive palaeobotanical sampling, evidence for the exploitation of grains, either domestic or wild, is very limited. A single grain of millet (Pennisetum sp.), which has been identified as possible domestic, was retrieved from the upper 0.50 m of deposit. Clearly, a sample size of one cannot be used conclusively to infer domestication. Nonetheless, grinding equipment was found in relative abundance (N = 18) and suggests that cereals did play a role in the diet of the Karkarichinkat inhabitants. Whether these grasses were domesticated has yet to be established. The abundance of domestic livestock at the site is consistent with a pastoralist economy. Of particular note is a burial feature containing a fully articulated cow with a set of post holes surrounding the grave pit found cut into the primary occupation levels in trench 1-B/C. The remains of disarticulated cattle bone, often charred and with cut marks, are indicative of dietary consumption. In contrast the purposeful inhumation of a complete cow suggests that cattle also played a role in the belief systems of KN05’s earliest inhabitants. Numerous cow figurines were also found at KN05, attesting to a recognition of the lactating function of cattle. Several rim sherds of pottery (N = 6) were also found with spouts, which may support the idea that milk, or milk products were part of the KN05 diet.

Interestingly, sheep and goat disappear from the sequence at 2.0 m, despite the continuance of cattle, whilst the number of fish remains significantly increases. The initial observations from the faunal analysis therefore suggest that in the earliest levels of occupation, cattle and fish were important resources. Soon after occupation was established, sheep and goat are introduced into the economy, and may indicate a shift towards more sedentary occupation. Similarly, grinding equipment is absent from the lower 0.70 m of deposit, and is generally more abundant on the surface, which may also be representative of increased sedentism and a shift towards a more diverse diet. Over two kilograms of fish bones were recovered from KN05, almost half of which came from a single pit (078) cut into the primary occupation layer of Trench 1-A. The taxa represent in this osteological assemblage include Clariidae, Synodontis, Tilapiini, L. niloticus, Bagriidae, Gymanrchus, Polypterus, Protopterus, and Mormyridaei. The catfish Clariidae and Synodontis alone account for over 75% of the assemblage. These remains provide strong evidence that fish constituted an important component of human diet at the site during prehistory. Stable isotope background The study of paleodiet through stable isotope analysis proceeds from the experimental observation that the isotopic composition of animal tissues generally reflects that of

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Fig. 2. Site plan of Karkarichinkat Nord (KN05).

Table 1 Radiocarbon determinations from KN05 Lab code

Date BP

Error 1r

Material

Context

OxA-16895 OxA-16896 OxA-16897 OxA-16919 OxA-16920 OxA-16973 OxA-16974 OxA-16975 OxA-16976 OxA-16898 OxA-16977

3894 3882 3856 4011 3922 3988 3853 3877 3913 3889 3986

32 32 32 33 33 32 32 33 33 32 31

Charcoal Euphorbiaceae sp. Charcoal Pennisetum sp. Charcoal Leguminosae sp./Vitis sp. Charcoal Charcoal Sterculia sp. Combretaceae sp. Charcoal

Context Context Context Context Context Context Context Context Context Context Context

the diet they consume. Such analyses utilize the variation in the ratios of the stable isotopes of carbon and nitrogen within ecosystems to measure the relative contribution of different resources to the diets of humans and other animals (DeNiro and Epstein, 1978, 1981). As some foods, such as maize and millet, have distinctive isotopic signatures, it is often possible to identify the consumers of these resources.

(032) (050) (081) (031) (037) (166) (077) (077) (147) (085) (087)

at at at at at at at at at at at

0.60 m 1.30 m 1.60 m 0.40 m 1.0 m 2.40 m 0.40 m 0.50 m 0.10 m (skeleton 1) 4.0 m 4.40 m

The stable isotope ratios of carbon (13C and 12C) and those of nitrogen (15N and 14N) are expressed in per mil (&) as d values: d ¼ ½ðRsample =Rstandard Þ  1  1000 where R = 13C/12C for the measurement of carbon and 15 N/14N for the measurement of nitrogen. The standards to which samples are compared are the limestone Vienna

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Fig. 3. Probability density distributions of calibrated radiocarbon measurements from KN05.

PeeDee Belemnite (VPDB) and atmospheric nitrogen (AIR) for carbon and nitrogen respectively. Most materials, including plant and animal tissues have less 13C than the VPDB, and their d13C values are typically negative. Carbon enters terrestrial food webs through the uptake of atmospheric CO2 by autotrophs. The fundamental variation in the ratios of stable carbon isotopes in these food webs stems from differences in the photosynthetic pathways of plants, categorized as C3, C4, and CAM. The overwhelming majority of plants utilize the Calvin Cycle (C3) pathway and have an average d13C value of 26.5& (O’Leary, 1988). The d13C values of plants relying upon the C4 pathway, mainly tropical grasses, are on average 12.5& (O’Leary, 1988; Van der Merwe and Tshauner, 1999). Plants utilizing a third pathway, Crassulacean acid metabolism (CAM), combine aspects of both C3 and C4 plants. The tissues of CAM plants have d13C values ranging from 11& when CO2 is absorbed at night, to 28& when CO2 is taken up during the day. The carbon isotope signature of animal proteins, such as collagen in bone and keratin in hair and nails, predominantly reflect the protein component of diet, as amino acids are preferentially routed from diet to be incorporated into body tissue (Ambrose and Norr, 1993; Tieszen and Fagre, 1993; Lee-Thorp et al., 1989). The proteins of animals are enriched in 13C relative to their diets by 4&. Considerable variability is observed in d13C values of fauna in marine and freshwater ecosystems as well as the consumers of such protein. Much of this variation stems from differences in the concentration of dissolved inorganic carbonates and thus the d13C values of aquatic plants within the ecosystem.

In general marine fish tend to be enriched in d13C, with isotopic values resembling those of C4 plants whereas the isotopic values of freshwater fish cover the spectrum from C3like to C4-like (Norr, 1995; White et al., 1993). In contrast the carbon isotope composition of the second major class of material analyzed in paleodietary studies, carbonates, more accurately represents whole diet including carbohydrates, lipids, and protein (Ambrose and Norr, 1993; Tieszen and Fagre, 1993; Schwarcz, 2000). Most of the mass of osseous remains is mineral, apatite and hydroxyapatite, 70% in bone and tooth dentin and 98% in enamel. The approximate formula of this compound is Ca10(PO4)6(OH)2. Structural carbonate occurs when –CO3 replaces –PO4 in the apatite crystals. This carbonate is derived from blood bicarbonate generated by the mitochondria during cellular metabolism and is on average enriched in 13C by 9.5–12& relative to diet (Ambrose and Norr, 1993; DeNiro and Epstein, 1978; Lee-Thorp et al., 1989; Passey et al., 2005). Dental enamel provides a higher fidelity record of paleodiet than bone apatite as enamel is denser, has larger crystals and is virtually devoid of organic matter (LeGeros, 1991; Elliot, 1994). Enamel is deposited during a discrete period early in an animal’s life and is not subject to later reworking. Analysis of known fossil grazers and browsers substantiate the reliability of enamel carbonate as a record of paleodiet (Lee-Thorp and van der Merwe, 1987; Cerling et al., 1997). The carbonate in the bioapatite of wild large herbivores is enriched by 14.6& relative to diet, whereas the carbonate of small animals used in feeding experiments is enriched by 9& relative to diet (Lee-Thorp et al., 1989; Tieszen and Fagre, 1993; Passey et al., 2005). Swine, the best digestive proxy available for humans, exhibit enrichment of carbonate by 10.2& relative to diet (Hare et al., 1991; Howland et al., 2003). Variation in isotopic spacing between diet and the carbonates of bone and tooth enamel is attributed primarily to differences in digestive physiology. The production of methane, CH4, by bacteria in the digestive tract results in the loss of isotopically light carbon and a concomitant enrichment of the remaining CO2 which enters the bloodstream and is later incorporated in the structural carbonates of bone and enamel. The greater methane production in the digestive tracts of ruminants is invoked to explain the enrichment of their bone and enamel carbonates vis-a`-vis rodents (Hedges, 2003; Passey et al., 2005). Using a linear mixing model, the percentage of C4 derived nutrients in an animal’s diet can be calculated using the following formula, adapted from Schwarcz et al. (1985): %C4 ¼ ðdcarb  d3 Þ=ðd4  d3 Þ  100 where dcarb is the measured value of the carbonate sample, d3 = 16 (the value of carbonate of pure C3 consumer) and d4 = 2 (the value of carbonate of pure C4 consumer). The oxygen isotope composition of carbonate in tooth enamel reflects the composition of the animal’s body water and is affected by diet, climate, and physiology (Longinelli,

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1984; Luz et al., 1984; Bocherens et al., 1996; Kohn, 1996). Body water is derived from atmospheric O2, the oxygen chemically bound in foods, and liquid water. As O2 in the atmosphere is relatively constant (Dole et al., 1954; Kroopnick and Craig, 1972), the primary sources of variation in body water composition are liquid water which is climatically sensitive (Dangaard, 1964) and to a lesser extent oxygen in food. Liquid water is ingested by herbivores and omnivores not only from surface water but also in roots, stems and leaves of plants. Although the isotopic composition of water contained within roots and stems is similar to meteroric water, leaf water is generally enriched in 18O (Gonfiantini et al., 1965; Epstein et al., 1977; Sternberg, 1989; Yakir, 1992). In addition to free water, plant and animal tissue also contains chemically bound oxygen with plants being enriched in 18O relative to animal tissues. The dietary patterning of animal oxygen isotope composition is complex with browsers and mixed feeders showing 18 O enrichment relative to grazers in some environments (Kohn et al., 1996) and the opposite trend being observed in other environments (Bocherens et al., 1996). Sponheimer and Lee-Thorp (1999b) have suggested that this discrepancy may reflect the relative contribution of surface water to an herbivore’s total water consumption. Although browsers and mixed feeders may obtain most of their water from the 18O enriched water in plant leaves, if they drink surface water on a daily basis their body water composition may not differ significantly from grazers which are obligate drinkers. In general faunivores and many primates are depleted in 18O relative to herbivores (Sponheimer and Lee-Thorp, 1999b). Methods and materials The skeletal remains of at least 11 humans were recovered from nine contexts at the sites of Karkarichinkat Sud (KS05) and Karkarichinkat Nord (KN05) (Figs. 1 and 2). The human skeletal remains from KN05 were exposed by deflation and were highly fragmented and degraded due to bioturbation, four wheel drive vehicles and exfoliation from wind and sun. Due to the disturbance of the remains, the determination of the grave orientation was not always possible, though in several cases skeletons appeared to be interred in supine positions with both arms and legs extended in E–W orientation. Poor protein preservation precluded direct radiocarbon measurements of human remains. In contrast the skeleton excavated at KS05 was both complete and better preserved than the remains from KN05. The skeletal remains from KS05 came from an intact burial cut into the Late Stone Age/Neolithic occupation mound and ringed with stone. These remains were estimated to date to the Islamic era (post AD1300) on the basis of the stratigraphy (the grave was cut through the LSA mound), their preservation (which included hair and cartilage), and the fact that the body was interred on its right side facing east towards Mecca.

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Estimates of age and sex were made using standard osteological criteria (Buikstra and Ubelaker, 1994; Bass, 1987). Criteria considered included cranial and pelvic morphology, dental eruption and wear, cranial suture and epiphyseal closure and overall robusticity. Due to the poor preservation of the remains, broad age estimates were used. In order to interpret human isotope values it was necessary to obtain an isotopic baseline using archaeological and modern fauna as well as modern plant samples. The remains of domestic Bos sp. and ovi-caprid (distinguishing between sheep and goats using skeletal remains is difficult) were recovered from both the surface and deep soundings. The skeletal remains of fish were abundant at the site and the taxa sampled included Polypterus sp., Gymnarchus sp., Claria sp., Tilapia sp., Synodontis sp., and L. niloticus. In addition modern fish from the Niger River and locally grown crops were obtained for analysis from a market in the town of Gao. Collagen was extracted from bone and dentin following procedures described in Richards and Hedges (1999). Isotopic analysis was conducted using a Carlo Erba 1108 carbon and nitrogen elemental analyzer coupled to a Europa Geo 20/20 mass spectrometer in continuous flow mode. The isotopic values of all samples were measured relative to tertiary laboratory standards of nylon and alanine whose isotopic values are calibrated with respect to IAEA and NBS standards which have internationally agreed values relative to VPDB. All samples were analyzed in triplicates in separate batches. Analytical errors are of the order of ±0.2& for d13C. The preparation and isotopic analysis of modern fish bones and plant samples was conducted by Hannes Schroeder. Samples of carbonate were prepared from teeth according to procedures outlined in Finucane et al. (2006). Enamel was analyzed by Norman Charnley in the Department of Earth Sciences, Oxford University. Powdered samples of enamel were reacted with 100% H3PO4 in a vacuum at 90 C in a common acid bath for six minutes. Isotopic measurements were made using a VG Prism IRMS. All measurements were made relative to the standards NBS19 and IAEA CO1. Analytical precision is better than .1&. Results None of the archaeological samples of human and animal bone or dentin yielded an appreciable quantity of collagen. However the modern samples from the Niger River provide a reasonable, if rough proxy for the carbon isotope values of the ancient fish of the nearby Tilemsi drainage. The eight modern fish collagen samples analyzed have a mean d13C of 18.4 ± 2.09& (Table 2). The carbon and oxygen isotope values of the human and animal tooth enamel are presented in Tables 3 and 4, respectively, and displayed in Fig. 4. The eight samples of human tooth enamel have a mean d13C value of 3.91 ± 1.31& and a mean d18O of 1.5 ± 1.31&. The mean value of the 28

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Table 2 Stable isotope values of human tooth enamel from Kakarichinkat Nord (KN) and Kakarichinkat Sud (KS) Sample KN1H KN5H KN11H KN12H KN13H KN17H KN20H KS2H

Trench 7 5 5 8 6

Context

Skeleton

Sex

Age

Tooth

d13C

d18O

160 151 148 159 148 153 149 3

8 10 3 7 2 6 5 11

M F? F F F? F? ? M

A A YA YA YA YA Child 30–35

LM3 RP2 LP1 LM3 LM3 LM3 LM1 LM3

2.6 4.3 3.8 3.1 3.1 3.7 4.3 6.4

1.9 2.8 2.3 1.2 1.4 1.8 1.7 1.6

3.9 1.2

1.4 1.3

Mean 1SD

Table 3 Stable isotope values of enamel carbonate of archaeological fauna from Karkarichinkat Nord Sample

Trench

Context

Taxon

Tooth

d13C

d18O

KN59A KN22A KN53A KN58A KN21A KN68A KN16A KN62A KN63A KN67A KN70A KN69A KN57A KN12A KN23A KN52A KN56A KN61A KN54A KN49A KN50A KN20A KN64A KN9A KN51A KN15A KN55A KN60A

B A A A B/C B/C B C B C B B C B B C B B B 3-A 3-A E B/C A A B/C D G

5 15 15 15 31 31 34 34 34 35 36 40 48 49 50 50 50 50 71 72 73 77 81 85 96 166 76/28 77-SPIT4

Bos Bos Bos Bos Bos Bos Bos Bos Bos Bos Bos Bos Bos Bos Bos Bos Bos Bos Bos Bos Bos Bos Bos Bos Bos Bos Bos Bos

M3 M3 M3 M2 M1 M1 M1 M2 M2 M1 M1 pm4 M1 M2 M3 M2 M2 M2 M3 M1 P4 M1 M2 M1 M1 I1 M1 M2

1.2 3.8 2.0 1.7 1.9 1.4 1.6 1.2 0.8 0.7 0.6 1.9 2.2 1.4 0.2 1.8 2.3 1.7 2.6 0.8 1.8 1.3 1.5 0.3 0.6 2.1 1.9 0.4

4.4 2.2 1.1 4.1 0.6 0.5 2.3 0.5 1.9 2.9 2.6 1.6 3.0 1.2 2.3 5.2 4.7 2.6 2.4 2.1 4.5 3.2 1.3 6.0 6.7 6.1 2.8 3.7

1.0 1.4

2.9 1.8

4.4 6.3 4.6 2.0

1.3 5.8 5.2 4.4

3.3 3.7

4.2 2.0

Mean 1SD KN19A KN10A KN66A KN65A

A B B D

16 31 31 124

Mean 1SD

samples of Bos sp. tooth enamel have a mean d13C value of 1.0 ± 1.37& and a mean d18O value of 4.2 ± 1.99&. The four ovi-caprid enamel samples have a mean d13C value of 3.3 ± 3.66& and a mean d18O value of 4.2 ± 1.99&. Human and ovi-caprid enamel samples have d13C values which are significantly lower than those of Bos sp. enamel

Ovi-cap Ovi-cap Ovi-cap Ovi-cap

M1 M M2 M2

(t-test, p < .001). Human enamel samples are also significantly depleted in d18O relative to those of the fauna (t-test, p < .001), though the d18O values of enamel from Bos sp. and those of the ovi-caprids are not significantly different (t-test, p < .001). Carbon and oxygen isotope values are not significantly correlated (d.f. = 37, r2 = .1502, p > .01).

B. Finucane et al. / Journal of Anthropological Archaeology 27 (2008) 82–92 Table 4 Carbon isotope values of modern fish from the Niger River at Gao, Mali Genus

d13C (&)

Bagrus Clarias Hydrocynus Lates Mormyridae Synodontis Teradon Tilapia

19.4 17.7 18.7 15.9 16.5 12.6 17.4 17.4

Mean SD

16.9 2.1

Values have been corrected for the industrial effect by adding 1.5&.

The d13C values of modern samples of millet and sorghum (Table 5) are consistent with the known values of C4 plants. In order to compare the modern resources with the prehistoric samples the carbon isotope values of fish and plants have been adjusted by +1.5& to compensate for the industrial effect (Indermuhle et al., 1999). Discussion The observed d13C and d18O enamel values are consistent with biogenic rather than diagenetic signals. If these isotopic signals were diagenetic, then diagenesis has differentially altered the carbon and oxygen isotope signatures of humans, Bos sp. and ovi-caprids. Given that these remains were recovered in close proximity in similar burial contexts, there is no obvious reason for differential diagenesis of tooth enamel. These findings are consistent with patterns observed in other studies of fossil tooth enamel (Lee-Thorp and van der Merwe, 1987; Bocherens et al., 1996; Cerling et al., 1997; Sponheimer and Lee-Thorp, 1999a,b; Van der Merwe et al., 2003; Lee-Thorp and Sponheimer, 2003; Kingston and Harrison, 2007) strengthening the proposition that enamel preserves dietary isotope signatures with high fidelity.

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The carbon isotope signatures of the human remains are consistent with the consumption of a mixed diet incorporating terrestrial animal protein (i.e. Bos sp. and ovi-caprids), riverine fish, and C4 plants such as millet and sorghum. Using the formula presented earlier, humans at KN05 consumed diets that were on average 85% derived from C4 resources. Due to the fact that the domestic animals at the site consumed diets comprised primarily of C4 plants (see below) the d13C value of their body protein is similar to that of millet and sorghum. As a result of this isotopic equifinality it is difficult to assess the precise extent to which human tissues were enriched in 13C directly through the consumption of C4 plants such as millet and sorghum or indirectly through the consumption of C4 grass eating animals (see Table 6). By establishing the relative trophic level of humans at KN05, analysis of the nitrogen isotope values of bone collagen could distinguish between the contributions of these resources. Unfortunately protein preservation at the site is poor. However, it should be noted that human consumption of lean protein is limited to 29–41% of energy consumption. At higher levels of protein consumption, hyperammonemia and hypereaminoacidemia are likely to result producing the clinical symptoms described as ‘‘rabbit starvation’’ (Cordain et al., 2000). Although animal protein was likely supplemented by fats, it is extremely improbable that the consumption of animal products alone could have produced the observed isotopic signatures. For humans to exhibit the observed d13C values solely as the result of carnivory, they would have to have consumed quantities of C4 animal protein comparable that of the big cats recovered in Member 2 at Swartkrans (Lee-Thorp et al., 1989). Rather it is more probable that C4 plants directly consumed by humans were the source of the enrichment in 13 C of enamel carbonate. It appears that C4 grasses such as wild Panicum sp. as well as possibly domestic Pennisetum sp. were a significant component of human diet. Humans are significantly depleted in 18O relative to the fauna at KN05. This finding is consistent with the acquisi-

Fig. 4. Bivariate plot of carbon and nitrogen isotope values of human and animal remains from KN05 and KS05.

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Table 5 Carbon isotope values of modern plant samples obtained in Gao, Mali Species

d13C (&)

Sorghum bicolor Sorghum arundinaceum Pennisetum glaucum Oryza glabberima Oryza glabberima

9.1 9.0 9.5 25.3 25.3

Table 6 Estimated average carbon isotope values of the diets consumed at Karkarichinkat Nord Taxa

Mean carbonate

Homo Bos Sheep? Goat? Fish Millet

4.0 0.8 2.0 5.1

Mean collagen

Plant

Mean diet 14.2 13.8 12.6 19.7

8.2 7.0 14.1 16.8 9.1

Modern fish and millet values have been adjusted by +1.5& to correct for the industrial effect.

tion of water from distinct sources. Whereas, both Bos sp. and ovi-caprids may have obtained much of their water from plant foods enriched in 18O, humans likely obtained the overwhelming majority of their water from the Tilemsi’s river. The lone sample from KS05, which dates to the Islamic era long after the desertification of the region, is an outlier with respect to both its oxygen and carbon isotope values. The higher d18O value of this individual may reflect greater reliance upon plant and animal products as sources of moisture relative to surface and ground water. The individual’s lower d13C likely reflects the growing importance of C3 cereals such as rice (Oryza glabberima). The contemporary Tuareg and Arab inhabitants of the Tilemsi Valley obtain rice through exchange with populations living along the Niger River and it is likely their predecessors of the Islamic era did the same. The increased consumption of animal products derived from C3 consuming browsers (i.e. goats) as a result of the region’s increasing aridity may also have contributed to the observed shift. Needless to say, generalization from a sample size of one is unwarranted. There is also an outlier within the ovi-caprid taxon. Whereas three of the ovi-caprids have d13C significantly lower than those of the grazing Bos sp., reflecting a diet of predominantly C3 browse, one individual has a d13C value indistinguishable from the cattle. Modern sheep and goats can be distinguished by the bimodal distribution of carbon isotope values as grazing sheep enriched in 13C relative to browsing goats (Balasse and Ambrose, 2005). The discrepancy in carbon isotope values observed in the fauna of KN05 may also reflect the ecological differences between goats and sheep. The depleted animals are likely goats, whereas the single enriched animal is probably a sheep.

Conclusions The evidence from KN05 suggests the site’s inhabitants exploited a mixed economy of wild and domestic resources. Although we do not yet have conclusive evidence that the C4 cereals consumed at KN05 were domestic, it is clear from both the carbon isotope signatures of tooth enamel and the grinding slabs that grain was a significant component of human diet. These findings are consonant with evidence for the exploitation of cereals (wild or domestic) by the Tenerean Culture of neighboring Niger from 5500 to 4000 BP (Haour, 2003). However, these d13C values also speak to the fact that C3 based resources, including fish from the Tilemsi palaeochannel (see the discussion of fish bones in Archaeological Context), contributed to the subsistence of KN05’s occupants. The exploitation of domestic livestock was clearly a major component of the subsistence at KN05, but the evidence from the Tilemsi postdates by several millennia the adoption of animal husbandry in Niger where the remains of morphologically domestic cattle have been found at Takene Bawat and in the Azawagh dating to 6000 BP (Haour, 2003). The d13C signatures of three of the ovi-caprids (probably goats) indicate that the environment surrounding KN05 was not exclusively dominated by C4 grasses but also contained an appreciable quantity of C3 plants. Such a finding is consistent with the existence of a Sahelian environment in the Tilemsi during the 3rd millennium BC and is consonant with paleoenvironmental records from other regions of eastern Mali which indicate that the Sahel once stretched to the north of the country. Further research will be necessary to refine our understanding of the transition to food production in the Tilemsi Valley. Additional investigation of the materials from KN05, including the analysis of residues on ceramics, will be required in order determine whether the grasses consumed at the site were wild or domestic and whether milk from domestic animals was being consumed by the site’s inhabitants. The excavation of additional stratified contexts will also be needed in order to obtain a sequence of human remains and thus a biogeochemical record of diet documenting diachronic shifts in diet.

Acknowledgments B.F.’s postgraduate research was funded by the Rhodes Trust and K.M.’s postgraduate research was funded by an award from the Arts and Humanities Research Council (AHRC). The fieldwork was made possible by further contributions from the AHRC, the British Institute in Eastern Africa, and the University of Oxford. We also thank the Direction Regionale de la Jeunesse des Sports et Arts, in Gao, our local excavation team, and Ayouba Ag Moussilim and Souleymane Ag Kiyou for all their invaluable help. Hannes Schroeder prepared the modern fish bones analyzed in this study and helped supply references cited in this

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