Experimental and archaeological investigations of backed microlith function among Mid-to-Late...

ORIGINAL PAPER

Experimental and archaeological investigationsof backed microlith function among Mid-to-LateHolocene herders in southwestern Kenya

Steven T. Goldstein1& Christopher M. Shaffer2

Received: 1 July 2015 /Accepted: 9 March 2016# Springer-Verlag Berlin Heidelberg 2016

Abstract This study takes an experimental and comparativeapproach in order to evaluate the circumstances driving thedeployment of microlithic tool technologies by food-producing mobile herders during the Mid-to-Late Holocenein southern Kenya. The predominately obsidian microlithsused by contemporaneous, but culturally distinct, herdingcommunities were replicated and used as arrow tips in archeryexperiments and within composite knives used in animal pro-cessing. This allowed for patterns of damage associated withproduction, different forms of projectile use, and butchery tobe identified on microlithic specimens and evaluated againsteach other to assess the criteria for diagnostic macrofractureand wear patterns reflective of each activity. Experimentallygenerated criteria were used to identify the most likely func-tions for microlithic tools in three archaeological assemblagesbelonging to early Kenyan pastoralists. The analyses showedthat while the same microlithic form is shared by culturallydistinct groups across a wide time range, these tools werebeing used to vary different functions that do not clearly cor-relate with subsistence economy, culturally affiliation, or timeperiod. Environmental variability and instability throughoutthe Late Holocene likely contributed to the persistence ofhighly adaptable microlithic toolkits. These data contributeto ongoing dialogues on the emergence and evolution of mi-crolithic toolkits.

Keywords Kenya . Composite projectiles . Impact fracture .

Experimental . Pastoral Neolithic .Microliths

Introduction

The debates surrounding backed microlithic elements haveintensified in recent years due largely to their implicationsfor the emergence and development of composite projectiletechnology. Versatile and functionally flexible microlithictools were integrated into diverse subsistence economics,across very disparate temporal and regional contexts.Microlithic tools are broadly and variably defined and caninclude small unretouched pieces and bladelets shaped by par-ticular patterns of retouch. The term “microlith” is used here torefer to any flake or blade segment backed by retouch alongone or more sides, with at least one sharp edge (after Elstonand Kuhn 2002; Hiscock et al. 2011). Identifying exactly howmicroliths functioned and why the technology became prom-inent in so many diverse economies is of ongoing importance(Ambrose 2002; Elston and Brantingham 2002; Elston andKuhn 2002; Forssman 2015; Lazuén 2014; Pargeter 2011).These efforts are important in inferring the broader environ-mental, economic, or social problems that stimulated the pro-duction of microlithic toolkits.

In Africa, researchers often discuss the origins of microlith-ic technologies and their connection to human “modernity” inthe Middle Stone Age (Ambrose 2002; Brandt 1986;Lombard 2005; Mcbrearty and Brooks 2000; Sisk and Shea2011). Societies in Eastern Africa continued to rely on geo-metric backed microliths well into the Later Stone Age andremained a diagnostic tool type for diverse food-producingentities in the Mid-to-Late Holocene. Between roughly 3200and 1200 bp, both mobile herders and hunter-gatherersemployed microlithic technologies throughout the Central

* Steven T. [email protected]

1 Department of Anthropology, Washington University in St. Louis, 1Brooking Drive, Campus Box 1114, St. Louis, MO 63130, USA

2 Department of Anthropology, Grand Valley State University,1 Campus Drive, Allendale, MI 49401, USA

Archaeol Anthropol SciDOI 10.1007/s12520-016-0329-9

http://crossmark.crossref.org/dialog/?doi=10.1007/s12520-016-0329-9&domain=pdf

Rift Valley and southwestern highlands of Kenya (Ambrose2002). These microlithic industries are also unusual in thatthey are almost exclusively produced on high-quality obsid-ians, rather than materials like chert or quartz. Economicallydivergent groups produced obsidian microliths that varied insize, but not in overall design. This presents a rare opportunityto study the variability in microlith use among groups withvery different lifeways, who were co-existing on the samelandscape, within the same environmental regime.

Previous experimental projects have produced a usefulblueprint for identifying fracture patterns related to projectileimpact with several raw materials (Yaroshevich et al. 2010;Pargeter 2011; Lombard and Pargeter 2008). It is, however,not known whether obsidian displays similar fracture mechan-ics during these processes. Building on previous studies, thisresearch evaluates the uses of backed obsidian crescentsamong early pastoralists in southern Kenya by comparingarchaeological specimens to replicas subjected to a range ofexperimental functions, including use within compositeprojectiles.

Background

The Pastoral Neolithic

Economic context for microlith industries in southern Kenya

Increasing aridity following the termination of the AfricanHumid Phase in the Early-to-Mid Holocene forced earlyAfrican cattle herders, whose strategies had developed in the“Green Sahara”, to disperse southward into Eastern Africa(Gifford-Gonzalez 1998; Marshall and Hildebrand 2002;Wright 2014). Domesticated forms of goat and sheep wereintegrated into mobile herding economies as a result ofcontact with groups in the Nile Valley. Ambrose (1982) hasargued that at least two independent migrations from the east-ern Sahara and Ethiopia were involved in the dispersal ofherders throughout Eastern Africa. Throughout these substan-tial economic and environmental changes, herders continuedto employ the blade and bladelet-based lithic technologies thatcharacterized Later Stone Age foragers.

Migrating pastoralists developed exchange networks tomaintain access to high-quality obsidians cross northernKenya by 5000 bp (Ndiema et al. 2009; Hildebrand andGrillo 2012), and subsequently in southern Kenya by ca.3200 bp (Ambrose 2001; Merrick and Brown 1984).Herders and foragers alike continued to focus on blade andmicrolith technologies throughout this “Pastoral Neolithic”(PN) phase, until the appearance of iron around 1200 bp(Bower 1991; Ambrose 1984). Abruptly retouched bladeletsegments, or geometric crescents (elsewhere referred to aslunates), are the dominant form for microliths in both forager

and pastoralist assemblages throughout the Pastoral Neolithicperiod (Fig. 1).

Microlithic crescents were manufactured by diverse pasto-ral groups as they spread across the micro-environmentalzones of southwestern Kenya (Fig. 2). Apparent variation inthe archaeological record makes it difficult to correlate thepersistence of microlith technology generally with any partic-ular economic strategy or environmental circumstance. TheEburran V lithic industries associated with foragers in theCentral Rift Valley change little in the Late Holocene, evenafter centuries of interaction with food producers (Ambrose2001). There is no apparent change in the ratio or design ofcrescents in pastoralist assemblages through time, even asstrategies shifted toward greater specialization in livestockmanagement and decreased reliance on wild fauna (Marshall1990, 1994; Simons 2004). There is also no direct evidence ofwild or domesticated plant exploitation until the very end ofthe Pastoral Neolithic period that might influence persistenceof backed pieces (see Wetterstrom 1991). With few classes ofcurated shaped stone tools, and a complete lack of bifacialtools, various Holocene populations in Kenya likely reliedon geometric microliths for a wide range of subsistence andprocessing tasks.

Early mobile herders in Kenya and their environmentalcontext

Mobile pastoralists are typically defined as peoples whoselivelihoods center on the care and provisioning of domesticat-ed livestock (Dyson-Hudson and Dyson-Hudson 1980;Davies and Hatfield 2007). Their mobility strategies are fo-cused onmoving herd animals to grazing, water, and salt. Thisdesignation does not require that people subsist only off ofprimary and secondary animal products. Maintaining suchrigid specialization through the inevitable drought cycleswould be practically impossible (Dhal and Hjort 1976;McCabe and Fratkin 1994). Evidence of hunting at pastoralistsites, past and present, is therefore interpreted as expectedstrategic variation within herding lifeways. Whereas the useof ceramics was once thought to be a sign of more sedentarylifeways, production and reliance on ceramics among highlymobile groups across Eastern Africa is well documented (seeGrillo 2014).

Fig. 1 Typical microlithic crescents for Pastoral Neolithic assemblagegroups; (a, b, c) Savanna Pastoral Neolithic (SPN) from site ofNarosura; (d) Elmenteitan pastoralist from site of Ngamuriak

Archaeol Anthropol Sci

Based on subsistence and settlement patterns, burial prac-tices, and ceramic styles, at least two herding societies co-existed with each other, along with local hunter-gatherers dur-ing this same time period. (Ambrose 1984, 2001). All of thesegroups produced high proportions of backed crescent-formedmicroliths. The earliest food-producing entity is the “SavannaPastoral Neolithic” (SPN), appearing in the archaeologicalrecord around 3200 bp in primarily savanna ecotones. TheSPN encompasses a high degree of inter- and intra-site vari-ability in lithic tool form, and ceramic traditions but withbroad economic similarities (Bower et al. 1977; Wandibba1980; Wright 2014). SPN herders practiced a mixed form ofmobile pastoralism, often supplementing their domestic econ-omy with wild resources (Gifford-Gonzalez 1998; Oyango-Abuje 1977; Marshall et al. 2011).

By 3000 bp, sites belonging to a new “Elmenteitan” cul-tural historical tradition began to appear in environmentsalong the western edge of the Central Rift and in the westernKenyan highlands. The Elmenteitan is marked by very distinctand consistent “Remnant-ware” ceramics, a largely standard-ized lithic reduction sequence, and nearly exclusive use ofobsidians from a discrete source on the upper slopes ofMount Eburru for lithic production (Ambrose 1984, 2001;Merrick and Brown 1984). Elmenteitan producers intensivelyspecialized in domestic stock within the Loita-Mara plains(Marshall 1990), but interactions with forager-fishers aroundLake Victoria may have prompted a larger inclusion of wildfauna in their diet in those areas (Chritz et al. 2015). Themicroliths at Elmenteitan sites are consistently much smallerthan those at SPN or forager sites, suggesting a difference inhow they were used by these groups (Ambrose 2002).

Patterns in microlith sizes are consistent despite distance toraw material source or blade size, making it likely that thisrepresents intentional choice rather than being a function ofreduction intensity. This is supported by evidence for regularaccess to obsidian through small-scale exchange networks(Ambrose 2001; Goldstein 2014). Additionally, there is sub-stantial overlap in the ranges of the SPN and Elmenteitangroups through time, so ecological conditions alone are notsufficient to explain the variation.

Climate proxies derived from lake sediments and isotopesdemonstrate a recharging of lake levels and expansion of sa-vannah grasslands across southwestern Kenya after 2900 bp(Ambrose and Sikes 1991; Chritz et al. 2015; Richardson andDussinger 1987). Even with overall wetter conditions, year-to-year variation was unpredictable (Wright et al. 2007).Serious droughts occurred on average once a decade (Ashleyet al. 2011; Fratkin and Roth 1990;Western and Dunne 1979).There is no apparent change in crescent form or rate of pro-duction within either forager or pastoralist assemblage groupsthrough this period (Ambrose 2001, 2002).

Archaeological samples

Three Pastoral Neolithic archaeological sites were included inthe comparative component of this study. Only a small num-ber of open-air Pastoral Neolithic habitation sites have hadextensive excavations producing large microlithic samples,and few of those are constrained to a single phase of occupa-tion. The microlith assemblages discussed here are from threeearly pastoralist sites that are single-period habitation sites andhave large associated lithic assemblages. These sites reflect a

Fig. 2 Map of the study area. a Kenya. b The southern Rift Valley and southwestern highlands with marked locations of Ngamuriak, Narosura, andProlonged Drifts. Elevations given in meters above sea level


range of early herder strategies across southern Kenya andthroughout the Pastoral Neolithic time period. While they dif-fer in terms of cultural-historical attribution, faunal profile,and micro-environment, backed crescents are abundant in allthree samples and were thus clearly important in the economiclivelihoods of herders in each location.

The site of Ngamuriak is a large Elmenteitan habitation inthe LemekValley, within a savanna grassland ecology near thebase of the Mau forest. Ngamuriak is likely a single-periodsite, dating to roughly 2040 bp (Robertshaw 1990).Ngamuriak has one of the largest faunal assemblages from aPN period site in the region, and 99.6 % of the identifiablefauna are domesticated cattle, sheep, or goat (Marshall 1990).This highly specialized pastoral strategy is typical of otherElmenteitan occupations in and around the Maasai Mara.Despite representing a large aggregation, there was little evi-dence for features or structures, and much of the archeologywas focused on midden deposits. A total of 80 obsidian cres-cents were randomly selected for analysis from thisassemblage.

The second sampled site is Narosura, a SPN site along theNarosura stream, near the edge of the Serengeti-Mara savan-na. Narosura has been roughly dated to 2740 bp, somewhatearlier in the PN sequence (Odner 1972). Over 96 % of theidentifiable faunal remains were identified as domesticatedcaprines and cattle, making Narosura one of the most special-ized pastoralist signatures within the SPN group. This is oneof the few Pastoral Neolithic period sites where post-holes arepreserved, and these are consistent in size and depth across thesite. Excavators interpreted this as evidence that the site likelyrepresents a single phase of occupation (Odner 1972).Narosura has a slightly higher amount of chert and quartz inthe total lithic assemblage; however, microlithic crescentswere still almost universally produced on obsidian bladelets.From this sample, 135 crescents were selected for analysis.

The third comparative sample is from Prolonged Drift,a large habitation site with several dense midden depositsdating to 2530 bp just south of Lake Nakuru (Giffordet al. 1980). Elmenteitan pottery dominates the assem-blage; however, the lithic industry at the site is moreproblematic. Analysis in the course of this study identified asubset of the assemblage with small microliths derived fromthe green obsidian types typical for Elmenteitan sites, as wellas blades with typical Elmenteitan platform preparation (seeNelson 1980). Other analyses have argued the lithics fromProlonged Drift are predominately SPN in nature (Ambrose1984). The odd inclusion of large numbers of thumbnailscrapers, more typical of Later Stone Age foragers than foodproducers (Ambrose 1998), further complicates straightfor-ward interpretations. The average microlith morphologies con-form to SPN standards; however, the distribution of microlithsizes suggests a bi-modal distribution of small (presumablyElmenteitan) crescents, and larger ones within the SPN range.

Considering the unusual co-occurrence of material culturefrom both Elmenteitan and SPN traditions, we argue that thesite should here be considered a “mixed PN” microlithicassemblage.

Cattle and caprines account for less than 20 % of thetotal fauna and a wide range of wild fauna including sev-eral large bovid species, as well as rhino and giraffe(Gifford et al. 1980). Prolonged Drift thus has by far thegreatest evidence for hunting within the sampled sites.The density of middens suggests it was a large pastoralistbase camp formed during a single, but prolonged, periodof occupation (Gifford et al. 1980). A larger sample of201 microliths were analysed from this sample, in orderto include and assess differences between the smaller andlarger microliths that may reflect both Elmenteitan andSPN forms (see Ambrose 2002).

Taphonomy and post-depositional damage

Many of the features that are used to identify and diagnosemacroscopic impact fractures can also be formed by post-depositional processes like human and animal trampling(Villa et al. 2009). It is therefore important to discuss thetaphonomic condition of the archaeological assemblages un-der consideration. Cattle and other livestock trampling is themost likely cause of post-depositional damage to these assem-blages. Trampling has been better evaluated through faunalanalyses of these sites. As most archaeological remains fromall sites come from mixed midden contexts, we assume thatthe same taphonomic forces were acting on both fauna andlithic assemblages.

At Ngamuriak, Marshall (1990) concluded that bone frag-mentation was due to intensive human processing, rather thantaphonomic forces like trampling. Faunal assemblages fromProlonged Drift also demonstrated very little evidence for ei-ther weathering or other post-depositional physical alterations(Gifford et al. 1980). Given the similarities between Narosuraand these sites (Bower 1991; Robertshaw 1990), assemblagesat all of the sample sites seem to have been rapidly buried withminimal post-depositional damage. While this may suggestpost-depositional damage tomicroliths was not enough to biasthis study, minor incidences of macrofracture consistent withtrampling (Pargeter and Bradfield 2012) were observed onboth microlithic and non-microlithic pieces from all of theseassemblages. Bending initiations on blades and blade seg-ments, crushed tool margins, and lateral snaps were all signsof potential post-deposition breaks within a context. Weattempted to avoid such contexts when selecting samples forinclusion in this study.

Exposure to fire is the most common form of surface alter-ation in Pastoral Neolithic sites, usually identified through bythe uneven development of a grey, opaque, surface lustre and/or visible internal fissures. Several Pastoral Neolithic


archaeological sites do exhibit very high rates of such modi-fication; however, the habitation sites sampled in this studyhave very little evidence of burning, patination, or other formsof chemical or physical weathering. A clear source of post-depositional damage is bag-wear resulting from most materialfrom these assemblages being curated in larger context or tooltype-specific bags. These sites were originally excavated be-tween 50 and 30 years ago, with relocation of the assemblagesand handling by analysts over these decades introducing po-tential for considerable scuffing scratching across artifact sur-faces. Due to the difficulties this imposed, it was not possibleto collect micro-wear data with the resources available, al-though we recognize the importance of integrating these anal-yses into continued research programs.

Microlith function: archaeological and experimentaldatasets

Microlith use in the archaeological record

Microliths in the archaeological record are most ofteninterpreted and discussed as projectile inserts (Clark et al.1974; Odell 1978; Garlake 1987; Nuzhnyy 1990; Lombard2011). Preserved arrows from early Egyptian tombs and eth-nographic examples from Kalahari foragers attest to the use ofmicroliths in composite arrows for hunting in African contexts(Clark 1959, 1977). There is also significant evidence for arole of microlith-tipped arrows in interpersonal violence in theAfrican Later Stone Age. Roughly 40 % of the individualsburied in the 13,000-year-old cemetery at Jebel Sahaba appearto have died violently from projectile or spear wounds, withsome individuals exhibiting over a dozen embedded micro-liths (Wendorf 1968). More recently, Lahr et al. (2016) havereported on an apparent episode of inter-group violence fromthe Late Holocene site of Nataruk in Turkana County, Kenya.There, they uncovered the skeletal remains of 27 individuals,10 of whom are reported to have suffered violent perimortemtraumas. In some cases, microlithic implements are in directassociation with human remains, including one incidence ofan obsidian microlith embedded in a human cranium (Lahret al. 2016). There is only one direct example for microlithsuse by Pastoral Neolithic groups, which again reflects inter-personal violence. A single individual recovered from the siteof Porcupine Cave on the Laikipia Plateau had a small micro-lith transversely embedded in ventral surface of a vertebra(Siiriäinen 1977) (Fig. 3). Despite the crescent having pene-trated the bone several millimeters, there is no sign of damageon the microlithic tip.

While projectile technology may have been a major formof microlith use in the PN, focusing narrowly on this possibil-ity may unduly ignore other possibilities. Backed pieces ofvarying morphologies have been employed as barbs intrusting spears used by Australian Aboriginal societies

(McDonald et al. 2007), in composite knives (Bar-Yosef1987; Hayden, 1973), and within sickles used for grain har-vesting (see Richter 2007). Furthermore, microliths may beused independently for personal or cattle scarification, orany other expedient cutting activity. Many researchers havealso invoked symbolic explanations for microlith production,complicating behavioral-ecologymodels (Hiscock et al. 2011;Wurz 1999; MacDonald 2013).

Despite the important role microliths have played asculture-historical markers and social arguments in PastoralNeolithic contexts (Ambrose 2002; Bower, 1991; Marshallet al. 2011; Robertshaw 1990; Simons 2005), there have beenno attempts to specifically reconstruct their use in these con-texts. As a result, we lack an understanding for what forcesinfluenced the visible variability among synchronic archaeo-logical groups in southern Kenya. The immediate goal of theproject is to assess patterns of macroscopic damage observedin the production and deployment of experimental replicas toevaluate whether projectile use and butchery can be identifiedarchaeologically. Addressing this issue will provide a startingpoint in understanding the role of lithic technologies in theexpansion and persistence of herding lifeways in the region.More broadly, the experimental project will address the stra-tegic flexibility of these technological strategies, which are sopervasive over a wide temporal and geographic range of eco-nomically and culturally diverse populations.

Macrofracture analyses

The application of macrofracture analyses is an efficient andpotentially powerful means of identifying evidence for projec-tile use in the archaeological record (Fischer et al. 1984;Hayden and Kamminga 1979; Iovita et al. 2011; Lombardand Pargeter 2008; Odell and Cowan 1986; Pargeter 2011;also see discussion in Pargeter 2013). In order for these

Fig. 3 Transverse microlith embedded into a human vertebra from thePastoral Neolithic period site of Porcupine Cave, Laikipia Plateau,southern Kenya (photo used with permissions from the NationalMuseums of Kenya)


methods to be applied effectively, archaeologists must estab-lish firm correlations between specific tool uses and discretefracture patterns and morphologies. A growing body of exper-imental projects is devoted to this task; however, much of themacroscopic research has been oriented toward the use ofcryptocrystalline silicate raw materials within projectile tech-nologies (Fischer et al. 1984; Barton and Bergman 1982;Bergman and Newcomer 1983; Dewbury and Russell 2007;Odell and Cowan 1986; Nuzhnyy 1990; Crombe et al. 2001;Sano 2012; Sano and Oba 2015; Shea 1988; Lombard andPargeter 2008; Yaroshevich et al. 2010).

The results of these experimental studies show that themost diagnostic features formed during projectile impact arestep-terminating bending fractures, secondary spin-off conesassociated bending fracture, and impact burinations (Bradfieldand Brand 2013; Fischer et al. 1984; Keeley 1980; Lombardand Pargeter 2008; Villa and Lenoir 2006). These features areformed when the force of impact is distributed across a largeportion of the tool edge or surface, causing the bending frac-ture. It is followed by “grinding”, resulting from the transfer ofresidual force through broken segments of the tool. In mostcases, the presence ofmultiple forms ofmacrofracture featuresand their distributions across both dorsal and ventral faces areused to identify projectile use (Dockall 1997; Pargeter 2011;Wilkins et al. 2012; see comprehensive review in Rots andPlisson 2014). These criteria become problematic in the lightof experiments demonstrating that at least step-terminatingbending fractures and impact burinations can be formed dur-ing tool production, or as a result of post-depositional tram-pling (Iovita et al. 2011; Pargeter and Bradfield 2012; Sano2009). With these realities in mind, it is clear that ongoingexperiments are necessary in order to identify patterns of mac-roscopic damage on different raw materials from a widerrange of activities and taphonomic processes. Comparisonwith microscopic wear patterns is also extremely importantin identifying projectile use, but is developed as a separatebody of research.

The experimental program carried out here was designed toestimate and replicate, as much as possible, both the types ofactivities carried out by early Pastoral Neolithic herders andthe implements involved in microlith use within these con-texts. The use of crescents within composite arrows is onefrequent explanation for this technology, and given the lateHolocene date for these assemblages, arrow use is highlyprobable. Even here, there is considerable potential for varia-tion within experimental variables that may bias results.

The fundamental influences on the formation ofmacrofracture are assumed to be arrow velocity, arrow mass,and the distribution of impact forces across the stone tip.Arrow speed and weight are the specific variables used tocalculate kinetic energy (Ek) in an arrow impact, which isconsidered by most modern bowers and archers to be the bestproxy for the potential damage of the projectile (but see also

Iovita 2011 for other variables). The equation for kinetic en-ergy is as follows:

Ek ¼ 1

2mv2

It is therefore arrow mass and arrow velocity upon impactthat should be the most important variables related to impactfracture formation (cet. par.) and should be the contexts inwhich impact fracture variability is reported. Given the low rateof decay in velocity over distance, launching velocity and im-pact velocity should be very close over experimental distances.

Identifying those variables that will significantly affect im-pact forces within an experimental program will aid in makingdecisions concerning the design of experiments and the estab-lishment of specific controls. Bow draw weight is sometimesused as a proxy for arrow velocity; however, draw weight itselfworks in concert with draw length, bow design, and arrowweight to affect speed. Morphology of the point, spinning/grain of the arrowshaft, and style of fletching, and environmentalconditions like wind speed and air pressure can all affect the Ekof an arrow, thus affecting the potential for damage. The increas-ing use of arrow chronographs to measure the velocity of eachprojectile fired is working to rectify this problem, and this meth-od was employed in the experiments presented here.

Role of arrow mechanics

The way in which the force of impact is distributed across apoint is also affected by a myriad of factors, with the morphol-ogy of the point itself, or the orientation of microliths within aprojectile, being the most substantive variable, followed by thecomposition of the target material. Another important variable isthe mode of hafting. Different adhesive substances will absorbshock differently and will also allow varying degrees of flexionupon impact. This is especially important in microlith experi-ments, as ethnographic accounts demonstrate that microlithsmay be simply “stuck-on” to a projectile with resin, rather thanbeing directly inserted into an arrow shaft (Clark 1977). Finally,and potentially most importantly, is the rawmaterial of the stonetip. Force will be differentially loaded across very sharp edgesrelative to less sharp edges, and the purity and crystalline struc-ture of different raw materials will affect how impact forcesmove through the tip. It is possible that different raw materialsexhibit different fracture patterns and fracture intensitiesresulting from projectile impact (but see Pargeter 2013).

The distribution of impact is also affected by the lateralmovement of the arrow tip as it makes contact with the target.This wobble is initiated when the arrow is forced to seemingly“bend” around the bow during release, such that it still flies inthe direction the archer is aiming at full draw, a phenomenonbetter known as the “archers paradox”. Arrows fired from a bowwill have far more of this flexion than bolts from a


crossbow. This is primarily a factor of stiffness of a shaft, or“spine”. Arrow shafts with an incorrect spine for the firingmechanism will bend either too much, or not enough, in flight.Experimental projects that do not take this into considerationmay be altering the observed degree or frequency of certainimpact fracture types that are related to the lateral movementof arrows. Assuming correct spinning relative to the bow, vari-ation between bows is likely minimal; however, it is currentlyunclear if the firing mechanics of cross-bows and other firingmechanisms produce significantly different fracture patterns.Additional variables like shaft length and thickness will alsoaffect flight patterns, but these typically co-vary with spine,bow design, and draw weight.

Given that many elements of projectile mechanics can in-fluence the intensity and patterning of stone tip damage, ex-periments designed to interpret archaeological specimensshould attempt to recreate the conditions in which those an-cient specimens were used. Ideally, the raw materials involvedin the experiments should reflect those in the specific contextbeing studied. Even within the relatively recent PastoralNeolithic of southern Kenya, some of the most important var-iables like bow draw weight are difficult to reconstruct. Awide variety of bow designs have been employed throughoutthe late Holocene, and into the present, by groups throughoutsub-Saharan Africa. In this instance, it is reasonable for bowdraw weight to be an experimental variable, such that thebows used to fire replica microlith arrows reflect the rangeof bows that were likely to have been used by prehistoricpastoralists. The ethnohistoric and ethnographic records sug-gest that late Holocene groups could have employed bowswith draw weight ranging from 40 to 80 lb (Speth 2010).Early pastoralists in Kenya employed several different typesof bows for different tasks, which is a common practiceamong most pastoralists in the area today. An additional com-plication for pastoral contexts is the use of mock-bows forbleeding cattle. This is a practice in which something as sim-ple as a branch latched with fiber is used to fire a sharpeneddart into the throat of a cow to create a shallow puncture fromwhich nutrient-rich blood is extracted and mixed with milk forconsumption.

Finally, the hypothesized projectile point replicas used inthe experiment must bemorphologically similar to those in thearchaeological record. For microlithic crescents, the most rel-evant dimensions are length, width, and thickness. The shapesand sizes will affect performance and the distribution of force.Previous studies have emphasized differences in the numberand orientation of backed microliths used in ethnographic andarchaeological projectiles (Nuzhnyy 1990; Yaroshevich et al.2010). Several possibilities for points exist, including oblique,double oblique, and transverse. With no previous use-wearstudies and only a single instance of definite transverse arrowuse, all of these possibilities must be considered. If microlithiccrescents were inserted along the shaft of an arrow, these may

have been hafted either perpendicularly to create an elongatedcutting edge, or obliquely as barbs.

Materials and methods

Experiments

In order to carry out these experiments, a total of 160 micro-lithic crescents were prepared to reflect the full range of mor-phologies found in Pastoral Neolithic contexts in southernKenya (See Fig. 4). Of these, 128 were used as points or barbswithin 83 prepared arrows, 17 were hafted into three compos-ite knives (modeled on the Australian taap (Hayden 1973)).Production and hafting of all microliths was undertaken byS.T. Goldstein. An additional 15 specimens were brokenduring production and were reserved for comparison tospecimens damaged from experimental use. This set ofexperiments represents only a small portion of both the totalpossibilities for prehistoric microlith use, but represents astarting point for understanding how formally shapedmicroliths were used by late Holocene pastoralists insouthern Kenya. Styles of hafting followed Yaroshevichet al. (2010, 2013) (Fig. 5).

Arrow design and experimental shootings

We chose to conduct two shooting experiments, using differ-ent bow types, to determine the degree to which this variablemight affect velocity and impact fracture. All of the arrowshafts used in these experiments were commerciallymanufactured wooden shafts professionally fletched with syn-thetic feathers tominimize variation. The use ofmultiple bowswith vastly different draw weights requires differentially sizedarrows with different spinning. Cedar arrow shafts 82 cm longwere used in conjunction with a 40-lb draw bow, and shorter70-cm-long arrows were used for the heavier 60-lb draw bow.Arrow shafts were manufactured by a bower to ensure correctspinning to the bows used. Microlithic tips were inserted intoadhesive compound applied to the blunted tips of the arrows,and barbs were inserted along the shafts. The adhesive was acombination of pine resin and animal hide glue, with the ad-dition of ochre as a binding agent. All of the microliths weremanufactured and hafted onto arrow shafts by one of us(STG). Following existing experimental reports and data onmicrolith orientations across Africa (Clark 1977; Odell 1978;Yaroshevich, et al. 2010), we employed a variety of pointorientations using the replicated crescents including:

1. Single oblique oriented at >30° angles; n = 202. Single oblique oriented at <30° angles; n = 233. Transverse; n = 194. Double oblique (always oriented at >30° angles); n = 21


Additionally, crescents were inserted in some arrows aslateral barbs (n = 12) or oblique barbs (n = 12). Total arrowweight for longer arrows grained to the 40-lb draw bow was26.12 g (SD = 2.89), and weight for the shorter arrows grainedto the 60-lb draw bow had an average of 23.55 g (SD = 3.70).The variation in weight within each arrow class was due toboth number of microliths per arrow and the amount of adhe-sive used.

Shooting

Shooting was conducted in two sessions inMarch of 2014 andwas performed by one of us (CMS), with STG and otherspresent to help document arrow speed and edge damage.

Both a 40-lb draw single curve bow and a 60-lb draw recurvebow were employed in respective sessions. In all sessions, thetargets consisted of freshly butchered pig rib cage overlaidwith a layer of untreated hair-on cow hide. A 16 × 14 × 12 inchblock of 10 % ballistics gel was placed behind the target, andpenetration depth was recorded for these sessions. This for-mulation was chosen to provide consistent contact conditionsthat would be highly likely to cause macrofracture. Distancebetween the archer and the target was maintained at 13 m forall archery sessions, in keeping with existing standards fortesting commercial bows. A major advantage of arrow tech-nology is that there is minimal decay in velocity over distance,and so reasonable variation in distance from the target hasminimal influence on arrow Ek at contact. Each arrow was

Fig. 4 Variation inmaximum length, maximumwidth, andmaximum thickness for experimental and archaeological microlith samples.Box andwhiskerplots include mean and interquartile ranges with outliers marked as open circles

Fig. 5 Microlithic tip and barb orientations used in the arrow firing experiments: (A) straight/oblique (<30°), (B) oblique (>30°), (C) double oblique, (D)transverse, (E) oblique barb, (F) straight barb


fired until (1) there was visible macrodamage on at least onemicrolithic element on the arrow, (2) a microlithic tip becamedislodged, or (3) the arrow penetrated the target ten timeswithout evidence of damage.

Microlith use in composite knives

In addition to the projectile experiments, 17 backed cres-cents were inserted within three wooden dowels with ani-mal hide glue. Unretouched edges were oriented parallel tothe long axis of the tool shafts. Composite knives of thiskind could have been used for a variety of tasks; however,the focus in these experiments was experimental butchery.One composite knife was used to butcher and process afreshly killed male deer that weighed approximately200 lb. Two knives were used during the de-fleshing of a250-lb, 3-year-old, female pig. These specimens were usedbecause they become opportunistically available for exper-imental projects. Each knife was used until the cutting edgewas significantly worn, and microliths were only removedif they became dislodged from the hafting resin. The use-life periods for the knives were 28, 15, and 32 minutesrespectively.

Analysed features

Microlithic crescent damage

At the conclusion of each experiment, each individualcrescent was placed in a labeled plastic bag with cursoryfield notes on the apparent points of fracture initiationrelative to how the microlith was hafted. Fragments thatwere dislodged from the tool/arrow shaft were collectedand bagged with the corresponding portions from the haftwhen this was possible. In several instances, we wereunable to recover portions of the microlithic elements af-ter they broke during impact. Microliths were cleaned andthen detailed patterns of fracture were recorded.Specifically, we recorded the type of damage, the positionof damage on the microlith, and the directionality of dam-age. The same procedures were used for experimentalproduction breaks and microliths used in compositeknives. Typically, this included identifying the morpholo-gy of edge damage in terms of initiation, propagation, andtermination. Additionally, we classified forms of snaps orlateral breaks.

In classifying impact fracture damage, we again choseto follow the coding protocol for single and multiple diag-nostic fracture types developed by Yaroshevich et al.(2010). These include subcategories of both single frac-tures and combinations of multiple fracture types. Theirexact specifications will not be repeated here, but are illus-trated in Fig. 6.

Results

Macrofracture damage

Microlith production damage

A total of 15 microliths were broken during the process ofbacking the crescents (Fig. 7). Of these, four were cross-sectional snaps that do not resemble any form of previouslyreported impact fractures. There were two cases each of snapswith extended hinge fractures and snaps with “tongued” frac-tures, similar to fractures that often occur during bladelet pro-duction (Fig. 7 (d)). They can occur on dorsal or ventral sidesdepending on how the crescent is being backed, but are alwaysuni-facial and can have spin-off fractures. However, becausebipolar percussion is the typical technique employed in mi-crolith production, some minor edge crushing along the op-posed face is possible. Such a step-terminating tongued frac-ture extending from a tip with edge damage on the opposedventral side could be misidentified as a “type a1” fracture.

Production damage on nine microliths took the form ofmicro-burinations. Three of these originated from the backededge and thus match the “Krukowski microburin” type asso-ciated with microlith production errors (Fig. 7 (c, d)). Bendinginitiations originate from the ventral retouched margin, re-moving a portion of that backing up to, and sometimes includ-ing, one tip. This could appear similar to either “type a3”impact fracture or bipolar damage observed in experiments(see below). In these replications, five burinations did origi-nate from the thinner and more fragile tips and extend alongthe backed ridge.

In two cases, these were accompanied by >2-mm spin offfractures. In only one case did themicro-burination extend downthe unretouchedmargin. The exact size and shape of these errorsvaried, but there is significant overlap with the “type b2” frac-tures observed on obsidian microliths used in arrows. The “b2”type fracture also resembles trampling damage on obsidian mi-croliths (see also Pargeter and Bradfield 2012).

Damage associated with composite knives

We discuss here only an overview of the macroscopic damageassociated with use in cutting tools in order to determinewhether or not such damage can overlap with reported mac-roscopic impact fractures. Wear resulting from use in compos-ite knives typically manifested as continuous bifacial edgedamage, typically extending less than 3 mm from the sharpedge (Fig. 8). Wear patterns were hierarchical, with edgedulling and chipping overlaying the longer feather-terminating flakes. Edge wear was rarely step or hinge termi-nating, and never displayed bending initiations, departingmarkedly from impact fracture expectations. Additionally,fractures propagated perpendicular to the working edge, rather


than emanating from a single point as would be the case in theevent of impact. Damage could be continuous along a largeportion of the edge, but more typically occurred in discretepatches. The majority of the wear observed was on the dorsalsurface, with only occasional minor attrition visible on theventral side.

The macrofracture patterns discussed above are typical forrepeated uni- and bi-directional wear on obsidian edgesworked against rigid and flexible materials (Setzer 2012).They are unlikely to be caused during a single impact event.Of all 17 obsidian crescents used in composite knives, onlyone broke in such a way as to possibly resemble a form ofimpact fracture. This specimen had two step-terminating frac-tures initiating from the sharpened dorsal edge that removedsmall portions of each tip. Only one microlith broke along alateral margin within the handle, and five had no macroscopicdamage at the conclusion of the experiments. Position withinthe composite knife, more than size or edge angle, had thegreates t impact on the format ion of edge wear.Macrofracture patterns associated with composite knife butch-ery within these experiments, though a limited sample, do notresemble patterns of impact fracture. More detailed

microscopic analyses of edge wear on experimentally usedobsidian microliths are necessary in order to more securelyidentify specific kinds of cutting and processing damage onarchaeological specimens.

Projectile results

Variables affecting rates of damage

Evaluating the performance characteristics of microlithic tipswas not the focus of this research project; however, a numberof arrow firings, penetration rates, and average penetrationdepths are presented in Table 1.

Obsidian microliths were on the whole surprisingly resil-ient, and many microlithic points withstood several direct andindirect contacts with bone without incurring damage.However, in many cases, the damage incurred was so cata-strophic that the debris would not be recognizable. In somecases, the microliths simply shattered, producing several sep-arate fragments. In other instances, several burinations propa-gated from the point of contact, removing large portions ofboth the backing and unretouched edge, with spin-off

Fig. 6 Types of diagnostic impact fractures with arrows showing directionfor fracture initiation: (a1) step-terminating bending fracture from steepangle, (a2) impact burination from steep angle, (a3) impact burination orlateral break originating from backed side, (b1) step-terminating scalarbreaks (or impact “crushing”) from transverse angle, (b2) step-terminating tip burination from transverse angle, (b3) step-terminatingbending fracture from transverse angle, (a1m) step-terminating bending

fracture from steep angle with inverse spin off fractures, (a2m) step-terminating bending fractures from bidirectional steep angles (resemblesbipolar damage), (b1m, b2m) multiple tip burinations from oblique angles,(cm) combination steep burination with bending fracture on opposite end,(d1m, d2m) combination of transverse step-terminating scalar fracture withtip damage. After Yaroshevich et al. 2010, Yaroshevich et al. 2013

Fig. 7 Typical forms of production breaks. (a) Oblique removal of a tip,(b) snap; (c, d) fracture initiating along retouched edges and extending atoblique angles along the microlith body. This type of fracture can produce

the “Krukowski microburin” type; (e) lateral snap with spin-off fractureearly in the backing process


fractures on both lateral and dorsal surfaces. The result inmany of these cases was essentially the crescent being“shattered” into several burin-like elements. In terms of basicpropagation, these catastrophic burinations are comparable tothe “a2” and “b3” fractures (Yaroshevich et al. 2010), butfragment to such a degree that it is unlikely that no piece couldbe reliably defined as “diagnostic”.

There was a slight difference in the ratio of traditional im-pact fractures to both the “no damage” and “shattered” cate-gories depending on arrow velocity. Lower velocity firingsproduced a higher rate of diagnostic impact fractures, withfewer tips experiencing no damage and fewer instances ofcatastrophic damage.

Both microlith size and orientation appear to be related tothe probability theywill accrueDIF, or other forms of damage.Obsidian crescents that were less than 18 mm in length had alower rate of breaking due to impact in such a way that pro-duced a DIF (χ2 = 10.26, df = 12, p < 0.05), although theywere as likely to shatter or snap as larger specimens.Transversely oriented microliths were most resilient to

damage regardless of arrow velocity, bow design, or crescentsize. In no instances did a transversely hafted obsidian cres-cent shatter or experience multiple burination-type fractures.

Within a sample of 45 arrow firings that resulted inimpact fracture (for which velocity was accurately mea-sured by the sensor), the total range of velocities was be-tween 132 and 168 m/s. There was significant overlap invelocities between both bows used, demonstrating thatbow draw weight alone is not a useful proxy in projectileexperiments (Fig. 9). When speeds were correlated witharrow weights to calculate kinetic energy (Ek), it produceda total range of 219.5–451.0 J [kg m2/s2] for arrow firingsthat produced impact fractures.

With the variation in arrow weight being very small, indi-vidual arrow velocity had the strongest influence on variationin total kinetic energy (r2 = 0.69, p < 0.05). Total kineticenergy appeared to be a poor predictor of the likelihood ofsingle-type impact fracture formation, which occurred evenlyacross the full range of arrow velocities and Ek (total range of219.5–451.0 J [kg m2/s2]). The majority (72 %) of multiple

Fig. 8 Damage on selectedexperimental specimens used incomposite knives: (a) minor edgedamage and attrition,discontinuous along the dorsalsurface with minor ventralcrushing; (b) feather-terminatingfractures up to 3 mm,discontinuous along the dorsalsurface; (c) scalar feather-terminating fractures <1 mm; (d)feather and step-terminatingfractures up to 3 mm, edgeattrition and rounding; (e)overlapping scalar damage<1 mmwith minor edge crushing;(f, g) other examples of irregularscalar damage up to 3 mm.Magnified images taken withDinoLite microscope at ×50magnification (a–c), ×35magnification (d), and ×45magnification (e); photoscales = 1 mm

Table 1 Performance features forarrows shot in all sessions Microlithic tip

orientationNo. ofpenetrations

No. ofricochets

No. ofmisses

Total shootings(N)

Mean depth(cm)

Oblique (<30°), n = 23 18 6 2 26 8.81

Oblique (>30°), n = 20 25 2 1 28 13.3

Transverse, n = 19 31 4 0 35 13.36

Double oblique, n = 21 17 6 0 23 7.81


impact fracture types occurred on arrows traveling with under300 J of total Ek. Catastrophic shattering events were morefrequent when total kinetic energy exceeded 280 J. In otherwords, slower and lighter projectile tips were more likely toallow a distribution of impact forces such that DIFs could beproduced, relative to faster and heavier tips.

Diagnostic impact fracture and crescent orientation

The relationships between DIF types (after Yaroshevich et al.2010) and crescent orientations are given in Table 2. Backedobsidian crescents were the only microlithic forms in PastoralNeolithic assemblages suitable for use in projectiles, and sothe following patterns are restricted to this single crescentic or“lunate” morphology.

Single-parallel fractures oriented parallel with the longitu-dinal axis of the crescent (types a1) occurred only in obliquepoints, and rarely in barbs (Fig. 10 (A)). These removals wereusually step terminating. Single fractures removing a portionof the tip along this parallel axis (type a2) were only observedin crescents with double oblique orientation, and in onestraight barb. This pattern may have been caused by moreloading force at the tips of double oblique points, rather thandistributed across the edges of single oblique points, or may beincidental. In one instance, a “type a2” fracture resulted in theremoval of a step-terminating burination that removed nearlythe entire extent of the unretouched edge.

The “type a3” fracture was observed in only one specimen.Yaroshevich et al. (2010) reports these were often producedduring arrow removal. Arrows in this experiment were re-moved by pushing them slowly through ballistics gel, ratherthan being pulled out through the bone, and this may partiallyexplain why the type was not visible here. Transversely haftedobsidian crescents did not incur any “type a” damage.

Single oblique and perpendicular forms of damage (typesb1, b2, b3) occurred on all point types in equal ratios, exceptfor the oblique points oriented at <30°. Type b1 perpendicularfractures on transversely hafted points were the most obviousand occasionally manifested as multiple overlapping conchoi-dal step-terminating fractures and multiple spin-offs (Fig. 11(a)). This seems to have occurred when an obsidian pointmade direct contact with the bone, essentially crushing theedge. Instances of type b2 fracture were largely restricted toperpendicular initiations that removed a retouched portion of atip; in many cases, this removal extended over 5 mm. Theseremovals resembled burinations and terminated in extremehinge features (Fig. 10 (E), Fig. 11 (c, i, j)).

Instances of multiple fracture types occurred at an overalllower rate, typically accounting for around only 40 % of thetotal fractured microlith assemblages, and under 30 % of thetotal sample when undamaged tips are included. When multi-ple fracture types could be identified, they were far more con-sistent in appearance than the single types, which were more

Fig. 9 Range of recorded velocities for arrows fired from the 40-lb drawweight bow (n = 60) and 60-lb draw weight bow (n = 37). Box andwhisker plots show range, mean, and interquartile values (there are nooutliers). Note: machine errors prevented recording velocities for everfiring

Table 2 Distributions of single and multiple diagnostic fracture types in the experimentally fired microliths by hafting orientation. Both 40- and 60-kgbow sessions are combined in this table

Haft Style Diagnostic single-fracture types Diagnostic multiple fracture types Total Shattered

a1 a2 a3 b1 b2 b3 a1m a2m b1m b2m cm d1m d2m

Oblique (<30) 6 2 1 2 3 1 1 1 17 2

Oblique (>30) 3 4 3 1 1 2 14 5

Double oblique 2 3 2 3 1 1 3 1 16 2

Transverse 2 2 2 1 3 2 12 0

Angled barb 1 1 2 1

Straight barb 2 1 1 1 1 1 7 1

Total 14 6 1 5 9 7 4 3 2 4 8 2 3 66 11


prone to variability. Fracture types a1m and a2m were rare,and restricted to points and a single barb that had more parallelorientations relative to the arrow (Fig. 10 (D), Fig. 11 (b)).Multiple oblique removals initiated at the tip and propagatingalong the retouched margin were the most abundant multiplefracture types. Type b1m fractures of this type consisted ofbetween two and four micro-burinations (Fig. 11 (d, h)) dis-tributed on both the dorsal, lateral, and ventral margins of theretouched edge. In no instances did multiple removals initiatealong the unretouched margin extending toward the tip. Inother instances, this type of multiple fractures was accompa-nied by a lateral break or oblique fracture on the opposite tip,which we included as type b2m.

The more complex, multidirectional, forms of impact frac-ture (types cm, d1m, and d2m) all occurred in very low fre-quencies in this experiment. The two obliquely oriented spec-imens with type cm damage technically matched descriptionsin Yaroshevich et al. 2010, but were very small (<1 cm). Theparallel portion of a type cm fracture on a lateral barb occurredwithin the hafted portion of the crescent. There were a fewinstances of type d2m damage; where multiple step-terminating oblique/perpendicular fractures were accompa-nied by an oblique/perpendicular fracture (Fig. 10 (f)). We

also included specimens where the perpendicular removal oc-curred closer to the center of the microliths, essentially split-ting it, in this category. As was the case with type b1 fractures,the step-terminating edge damage tended to be quite exten-sive. The perpendicular breaks which were identified as typed2m are not so much separate features from this edge damage,but rather tend to be instances where the b1 portion extendedfar enough to fracture the microliths.

In addition to the diagnostic impact fracture formsdiscussed above, some crescents exhibited forms of bipolardamage as a result of impact. This could be wide conchoidaldamage extending from the retouched margin along the dorsaland/or ventral surfaces (Fig. 11 (g)), or fractures initiatingfrom the retouched edge and removing a large portion of themicrolith tip. These were likely caused when the force loadedthrough the microliths and into the mastic and arrow shaft,which resisted this force and loaded it back into the microlith.The identification of these fractures as “bipolar” is very mucha factor of having observed this occur during experimentation;otherwise, it would be very difficult to distinguish this type ofdamage from production errors or trampling.

Given the low frequencies of DIFs in the experimentalsample, it is difficult to associate any specific patterns of

Fig. 10 Representative impactfractures on experimentalmicrolithic arrow tips. (A)Oblique fracture along sharp edgeof oblique microlith tip andmultiple oblique fractures alongdorsal and ventral surfaces of astraight barb; (B) minorperpendicular fractures on ventraland dorsal surfaces on transversebarb; (C) oblique burinationextending from a sharp edge tipremoving a large portion of thebacked margin, with ventral spin-off fractures on large obliquemicrolith; (D) opposed parallelfractures extending toward thecenter of the microlith from bothtips on different surfaces of a <30°angle oblique microlith; (E)multiple oblique micro-burination-type removalsextending from one tip along bothdorsal and ventral surfaces of anoblique microlith; (F) multiplestacked perpendicular step-terminating fractures initiatingfrom the sharped edge along boththe dorsal and ventral surfaces,along with a parallel orientedlateral break (likely caused bysecondary friction during impact)


crescent damage with specific orientations in a projectile. Thisis especially true for trying to identify barbs, which were veryrarely damaged at all in experiments. Taken as a whole, it isclear that backed obsidian crescents do experience identifiableand diagnostic impact fracture types that have been identifiedfor other microlithic morphologies and raw materials.Secondly, while some types do overlap with production errorsand trampling damage, impact fractures do not resemble theform of edge damage obsidian crescents experience as a resultof cutting or butchery activity. Multiple fracture types remainthe most convincing examples of macroscopic damage causedby projectile impact.

Comparison to archaeological samples

Having defined a range of macroscopic fracture patterns fromprojectile impact, butchery-related damage, and productionbreaks, we analysed archaeological samples from three earlypastoralist sites in southern Kenya: Ngamuriak (Elmenteitan),Narosura (SPN), and Prolonged Drift (mixed PastoralNeolithic). As discussed above, we did not sample from

contexts where there was clear evidence for trampling or otherpost-depositional damage. Even so, several microlith cres-cents included in our samples did exhibit damage consistentwith trampling. Additionally, many specimens had forms ofdamage that could not easily be assigned to production breaks,trampling, or other forms of wear, and compose an “indeter-minate” category of macrofracture. The total samples andrates for different fracture or wear types are summarized inTable 3. A view of these data demonstrates how low ratios ofmacroscopic damage are overall in these assemblages.

Every designation for impact fractures defined byYaroshevich et al. (2010, 2013) and used for the experimentalportion of this study was identified on at least one archaeolog-ical specimen, except for types a3 and b2 fractures. A sampleof the patterns of damage on archaeological specimens withpotential impact fracture, as well as a few likely taphonomicbreaks due to trampling, are illustrated in Fig. 12.

The sites of Prolonged Drift and Ngamuriak had thehighest proportions of identified impact fracture (15.9 and21.3 %, respectively). Frequencies of macrofractures aredisplayed in Fig. 13 (single macrofractures) and Fig. 14

Fig. 11 Photographs of projectile damage on experimental microlithictips. (a) Stacked perpendicular scalar fractures along the unretouchededge and oblique removal of tip on a transverse point; (b) parallel step-terminating bending fractures on ventral surface of a <30° oblique point;(c) oblique removal of tip initiating from the sharpened edge andextending toward the retouched side of an oblique point; (d, h) multipleoblique fractures resembling micro-burinations with the same point ofinitiation on the sharp edge of an oblique point; (e) fracture extendingfrom a tip across the microlith body at a perpendicular angle of an obliquepoint; ( f ) fracture extending across a microlith body at an oblique angle

removing a portion of the backing on the dorsal side of an oblique point;(g) bipolar damage on the ventral surface of a transversely hafted point; (i)tip removal in the form of a burination extending from the sharpened edgealong the retouched margin of an oblique point; (j) removal of a tip with astep-terminating oblique fracture on the ventral surface of a <30° anglepoint; (k) blunt angle removal of a tip with stacked step-terminatingconchoidal scars initiating at oblique-to-perpendicular angles to theunretouched edge; (l) perpendicular edge damage on a transverselyhafted point (see Fig. 9f) (photographs taken using DinoLitemicroscope camera at ×50 magnification, scale = 1 mm)


(multiple macrofractures). Note that the overall frequency ofinstances at Prolonged Drift is much higher, but it is also amuch larger assemblage. Despite the disparity in sample sizes,the ratio of both single and multiple macrofracture types arevery similar at both of these sites. Parallel tip removals (typea1) and oblique-to-perpendicular step-terminating damage onthe unretouched margin (type b1) were the most persistent atboth sites. These are both single impact fracture types and so

are far less definitive than the multiple impact fracture types.The sample of the latter at both Ngamuriak and ProlongedDrift is quite small, with only multidirectional tip removals(type b1m) and lateral step-terminating damage in conjunctionwith a tip removal (type d1m and type d2m) occurring on asignificant number of specimens. Nearly all of the impactfractures observed in this sample were on microliths withinthe typical Elmenteitan size range (>20 mm in length).

Table 3 Summary of different types of damage identified in archaeological samples

Geometric crescents Non-use-related damage Impact fractures Utilization

Site Total Obsidian n sampled Trampling Indeterminate No. of single DIF No. of multiple DIF

Ngamuriak 120 115 (95.8 %) 80 1 3 10 7 8

Narosura 215a 189 (87.9 %) 135 4 5 6 4 8

Prolonged Drift n/ab n/a 201 7 13 37 9 31

a This count includes one quartz crescent not reported in Odner 1972b This assemblage has not yet been systematically analysed or described

Fig. 12 Archaeological microlithic crescents with edge damageconsistent with experimental macrofracture damage from Ngamuriak(a–g), Narosura (h–p), and Prolonged Drift (q–cc). Type a2 damage: h;type b1 damage: a, o; type b2 damage: f, g, i, l, y; type b3 damage; c, n, s;type a1m damage:w, x; type a2m damage: z; type b1m/b2m damage: b, e,

k, p; type d1m/d2m damage: d, q, r, v. Specimens exhibiting edge wearconsistent with use as a cutting edge (i, j, m, u) and specimens with edgedamage consistent with trampling (t, bb, cc). Arrowheads show probabledirection of “impact” forces relative to the dorsal surface


Backed crescents from Narosura had the lowest rate ofidentified macrofractures, accounting for only 8.1 % of thetotal assemblage. We were able to identify several single-type fractures that are morphological matches to experimen-tally observed macrofractures; however, only instances of twoor more micro-burinations originating from a tip (type b2m)were truly convincing. Multiple fracture types were exceed-ingly rare in this sample, and so it overall presents very littleevidence for microlith use within projectiles.

Additional, non-diagnostic, forms of damage were also ob-served on specimens from all sites. Aside from clear produc-tion errors or snaps (none of which were included in the anal-yses above), crescents from these sampled sites exhibited ev-idence of edge wear. This includes 31 specimens fromProlonged Drift (15.4 %) and 8 from Ngamuriak (6 %) andNarosura (10 %). Edge wear was typically bifacial, but some-times unifacial, and restricted to within 1–2 mm of the cutting

edge (see Fig. 12 (j, u, m)). Wear distribution tended to befairly evenly distributed across the working edge for bothunifacial and bifacial pieces. This pattern is more similar tomacroscopic wear observed in cutting experiments than it is toimpact fractures. The more intensive and un-clustered patternsof edge wear in the archaeological samples could be a result oflonger periods of implement use, or use on harder materialslike wood or bone. If this is accurate, there is about as muchevidence for microliths being used in cutting activities as thereis for use within composite projectiles, given the sampledassemblages from these sites.

Consideration of post-depositional damage

As discussed above, post-depositional and taphonomicforces can also be a source for damage on microlithicpieces. We consider trampling by humans and livestockthe most likely, and most well studied, source for macro-scopic damage that may resemble impact fractures withinthe archaeological assemblage. Pargeter and Bradfield(2012) reported that the most frequent forms of tramplingdamage were artifact snaps, notches, and hinge-terminating flake scars. In those trampling experiments,less than 3 % of specimens exhibited trampling damagethat overlapped with diagnostic forms of impact fracturenoted from other macrofracture studies. The criteria here,adopted from Yaroshevich et al. (2010), do not include anyof these common taphonomic damage types, and so mis-identification of post-depositional breaks was minimal, andwithin acceptable ranges of error (see Sano 2009).

Several archaeological specimens with macrofractures thatwere consistent with trampling were identified and not includ-ed as potential impact fractures. A few examples are illustratedin Fig. 12 for comparison. Illustrations 12t and 12b showpieces with wide and irregular notches with bending initia-tions, with lateral snaps near a tip. The microlith illustratedas 12 cm3 has a remnant dorsal flake scar from bladelet pro-duction and an irregular profile of steep ventral damage allalong the un-backed margin. These features were unlike anyimpact-related features reported here or elsewhere, and so thispiece was also considered to be a product of taphonomic dam-age. Any microlith with probable trampling following thesecriteria was also excluded, even if there was additional hingeor step-terminating bending fractures. A few specimens (12r,v) also display notch-like damage, but in these cases, the dam-age appears to originate in a single focused point and is com-bined with tip burinations and/or associated ventral damage.In these cases, we felt that the resemblance to experimentaltransverse tip damage (See Fig. 10 (F)) was strong enough toallow their inclusion as probably impact. In all cases, multipleimpact fracture types, preferable across both ventral and dor-sal faces, were required to even suggest use as projectile tipsor barbs.

Fig. 13 Frequencies of impact fracture types for specimens with onefracture type for archaeological microlithic crescent assemblages fromNarosura (SPN), Ngamuriak (Elm.), and Prolonged Drift (Mixed PN)

Fig. 14 Frequencies of impact fracture types for specimens with multiplefracture types for archaeological microlithic crescent assemblages fromNarosura (SPN), Ngamuriak (Elm.) and Prolonged Drift (Mixed PN)


Discussion

Experimental patterns

The experiments conducted in replicating and using obsidianmicroliths demonstrated that they can incur forms of DIF iden-tified for microliths in previous studies. While the use of mi-croliths in composite knives produced a categorically discretepattern of damage, production errors and trampling can poten-tially produce features morphologically similar to some single-fracture features also caused by impact. Additional experi-ments using microliths for a wider variety of tasks may broad-en the degree to which non-impact-induced fractures overlapwith DIFs. It is not impossible that some or all of what weidentified as edge-originating impact fractures in the archaeo-logical samples were also derived from non-projectile activity.

Specific patterns in impact fractures observed here relatestrongly to the mechanical properties of obsidian as a rawmaterial, as well as the specific crescent form for PN micro-liths. It appears that higher arrow velocities in conjunctionwith the extremely sharp unretouched obsidian edge permitsmost of the impact forces to be distributed across the face ofthe point, rather than loaded into the edge itself. When force isloaded into the obsidian crescent at these velocities, it is morelikely to result in multiple planes of fracture or burination,shattering the point. At lower arrow speeds, the lower overallKE does not permit the obsidian blade to cut through tissues aseasily, and loads more force into the microlith. The result ofthese mechanics is the observed result that obsidian microlithstend to either not fracture at all, or fracture catastrophicallyupon impact. This increases the difficulty of detecting theiruse in projectiles within the archaeological record. Rates ofdamage on barbs were especially low in these experiments,permitting very little discussion of their use.

In terms of arrow performance, transversely hafted cres-cents were the least likely to fracture and had a very highaverage penetration depth relative to other hafting modes.These observations match those made by Yaroshevich et al.(2010). Double oblique orientations, not surprisingly, causedthe most tissue damage and largest wounds, but at the cost ofreduced penetration. Neither of these are necessarily the most“efficient”, since hunting strategies, use of poisons, and othervariables can vary depending on the type of prey being huntedor the hunting customs of a particular group. Furthermore, ifthe advantage of microlithic elements is that they are replace-able parts, it is unclear why durability would be advantageous.In other contexts, barbs are specifically designed to fractureand detach within a target. The relationships between pointangles and fracture patterns are discussed elsewhere (see Odelland Cowan 1986).

Rates of impact fracture were so low in these experimentsthat we are not confident that specific DIF types correlate withspecific microlithic tip orientations within projectiles. This is

true for both single- and multiple fracture types; however,some preliminary patterns were observed. Multiple fracturesoriginating along the unretouched edge were more typical oftransverse points, whereas fracture types consisting of multi-ple micro-burinations originating along the sharp edge of a tip,removing that tip at a low angle, occurred at a higher rateamong oblique tips.

Interpretation of archaeological assemblagesand implications for microlith function

There appears to be significant variation in potential micro-lithic orientations within projectiles, rates of projectile impactdamage, and use of microliths outside projectiles. It is difficultto tell, given the few sites with large microlith assemblages, ifthis variation exists between individual sites or varies by ma-terial culture affiliation (i.e. Elmenteitan or SPN producers).There is more evidence of multiple perpendicular and obliquefractures originating from the sharp edges of microliths at theElmenteitan site of Ngamuriak and at Prolonged Drift, sug-gesting more frequent use of transverse orientations. Evenbetween these samples there is variation, with ProlongedDrift having a much higher rate of deep parallel fracturesinitiating at a tip and propagating along either the sharperlateral margin or along a ventral/dorsal surface. Macroscopicdamage is rare in the SPN assemblage from Narosura, andconsists largely of oblique damage to tips, including multiplemicro-burinations along backed and sharped margins of cres-cents. Based on experimental observations, this might corre-late with oblique hafting orientations. Experimental barbswere rarely damaged, making it difficult to speculate aboutthe use of crescents as barbs in these sampled. In other con-texts, the use of geometrics as points (as evident here) corre-lates with a decreased use of arrow barbs (Crombe et al. 2001).

The signature for projectile use is stronger in the smallercrescent forms from both Ngamuriak and Prolonged Drift,although sample sizes may bias this inference. Some studieshave observed that the crescent or “lunate”microlithic form isless prone to impact damage than other microlithic forms,especially when hafted transversely (Yaroshevich et al.2010). The smaller crescent forms, in experiments here, werenotably resistant to macrofracture in transverse orientations aswell. Early East African herders may have focused on thecrescent form with preferred transverse orientations for arrowuse due to their durability as projectile tips. This assumes aneed for highly effective and predictable projectile armaturesby these groups. Smaller, more consistent, forms would allowfor more predictable arrow kinetic energy and flight paths.Such a hypothesis is hard to test, given both the resistance ofobsidian microliths to archaeologically identifiable forms ofdamage. In addition, arrows brought back to site with dam-aged microliths may be only a small percentage of those ac-tually used by pastoralists.


Obsidian crescents would be efficient projectile tips, butthe overall ratios of macrofracture is low in these sites, andboth Ngamuriak and Narosura appear to have had little huntedfauna in the assemblages. So what was driving microlith pro-duction? Therefore, there are several, non-mutually exclusive,possibilities for how early herders in these environments mayhave used composite projectiles. Breaking down and evaluat-ing these possibilities, and their contexts and implications,may yield a new set of insights into the role of the sametechnology elsewhere in space and time. Microlithic projec-tiles themselves may have been employed for a diverse rangeof needs, including protecting herds from predators, raiding,hunting (subsistence or ceremonial), or cattle bleeding.

The Pastoral Neolithic is characterized environmentally byunpredictable rainfall patterns, regular droughts requiring rap-id changes to subsistence strategies, and culturally by the ex-istence of multiple spatially overlapping archaeological enti-ties with divergent economies. Considering these variableswith the added complication of tremendous ecological diver-sity across southern Kenya, there were likely frequent shifts in(a) rates and intensities of mobility strategies, (b) the diversityof wild resource base being exploited, and (c) intensity of wildresource exploitation and its importance in pastoralist econo-mies (see Bower 1991; Chritz et al. 2015; Marshall et al. 2011;Prendergast and Mutundu 2009). Specifically, Ambrose(2002) discussed similar environmental stress as one of manypossible reasons for the adoption and persistence of microlith-ic technologies in Eastern Africa. The co-occurrence of high-impact fracture rates and wild fauna at Prolonged Drift fit themodel posed by Gifford et al. (1980) wherein large concen-trated settlements near dependable permanent water sources ingood environmental conditions would show more evidencefor specialized herding. It is the shorter-term sites near tempo-rary water sources, or during droughts, where hunting wildfauna would become a necessary fallback strategy.

Moreover, these stresses may also lead to increased com-petition between the diverse social groups occupying southernKenya at this time. The multiple associations of microlithicarrow tips with incidents of violence specifically in this regionrequire considering the possibility that inter-group violenceplayed an important role in maintaining microlithic arrowtechnologies through the Holocene (Lahr et al. 2016;Siiriäinen 1977). Even if actually episodes of violence wererare, the threat of events like cattle raids and territorial con-flicts would incentivize maintenance of an effective and reli-able projectile technology by people who appear to have beendoing little hunting. Certainly, the prevalence of cattle raidingby small groups is well documented in the ethno-history ofEastern Africa and could have been a concern for people in thepast (see Galaty 1982; Gray et al. 2003; Tignor 1972).

Maintaining microlithic toolkits would become importantso that, in the event of unpredictable drought, livestock epi-demic, or catastrophic raid, projectile technology could ensure

economic resilience. The data presented, as we interpret it, isconsistent with the argument presented by Ambrose (2002)for environmental uncertainty playing an important role inthe deployment of microlithic toolkits. Microlithic productionand use appears related to decisions about economic strate-gies, and it is possible that many economic strategies mayexist within a single environmental regime. The apparent as-sociations of impact fracture on smaller microliths and someform of edge use on larger microliths may have implicationsfor understanding the technology more broadly. Microlithictechnologies persisted into the Pastoral Neolithic period duethe complex nature of mobile food production in the mid-to-late environments of eastern Africa. At least within thePastoral Neolithic, it is probably that morphology was shapedby economic divergences between pastoralist groups, as evi-denced by differences in proposed microlith use betweenNgamuriak, Narosura, and Prolonged Drift.

Even if there is a primarily economic difference drivingmicrolith use among Pastoral Neolithic groups, it is prob-able that the size differences between Elmenteitan and SPNsites could have been maintained for social reasons.Material and stylistic differences in “utilitarian” oftenserve as important expressions of group identity amongEast African pastoralists. A particularly apt example isthe strict preference for particular ceramic vessel formsby Samburu and Rendille herders in northern Kenya.Despite ongoing co-existence, interaction, trade, and ofteninter-marriage between groups, they maintained rigid ma-terial culture differences specifically to mark identity andaffiliation (Hodder 1977, 1979). The possibility that stonetools, specifically microliths, which were used in a similarway in the PN is worth further discussion and testingthrough continued analyses. Models proposed here forexplaining microlith function can be tested by expandingthese analyses to additional assemblages and expandingthe score of research to include micro-wear studies.

Conclusions

Replication and experimental use of microlithic elementscan be used to identify particular fracture types anddistributions related to different tasks, aiding inreconstructing how microlithic technologies were de-ployed in the past. Experimental data presented here focuson the patterns of damage on obsidian crescents reflectingthe range of cultural variability within the PastoralNeolithic of southwestern Kenya. Comparisons show thatthere is some morphological overlap between impact-related fractures and those caused during production, butthat microliths used within composite knives show pat-terns of edge damage that are largely distinct from eitherproduction or projectile impact.


The rates at which obsidian microliths used within arrowsexhibited diagnostic impact fractures were also quite low forall tip orientations and are partially related to arrow velocity.Many of the microliths that did fracture during impact hadonly single-impact features or shattered catastrophically.Truly diagnostic fractures were multi-directional and/or in-volved the removal of several micro-burinations across differ-ent faces of the microliths, initiating from a single point. Thesewere rare in the experiments. In conjunction with taphonomicissues, these data form the grounds for arguing that it is rela-tively difficult to firmly identify arrow use in the archaeolog-ical record from microlith damage, even when it is known tohave occurred. Given the rates of damage in these experi-ments, it is also difficult to reconstruct the ways in whichobsidian crescents were hafted in arrows.

Analysis of microlithic assemblages from three PastoralNeolithic habitation sites revealed variable rates for potential(single feature) impact fracture, diagnostic (multiple feature)impact fracture, and edge wear related to use for cutting andbutchery. How microliths were used, potentially hafted in ar-rows, and rates of visible impact fracture all appear to varybetween sites and possibly between different pastoralist cul-tural groups. A larger sample of Pastoral Neolithic microlithicassemblages from across the region would improve resolutionon the fundamental forces shaping this variation. Microlithicforms are consistent across environmental variability and var-iation in subsistence strategies, and yet the ways in whichmicroliths were actually used were quite different betweenindividual sites. We argue that within these Holocene con-texts, the manufacture and use of microliths is not inherentlyconnected to arrow use, and microlith design is not solelydetermined by attempts to optimize them for any particularstrategy. Understanding the longer term trajectories of micro-lith use in East Africa is also vital, requiring analysis of abroad range of Later Stone foragers and food producers.Investigating the variation in microlithic morphology andfunction within a broader range of economic, environmental,and social contexts provides a more comprehensive under-standing of why these technologies developed, changed, andwere ultimately abandoned in East Africa and elsewhere.

These interpretations will continue to be refined by addi-tional experiments using replicated obsidian crescents for awider variety of tasks and comparing the datasets to an ex-panded archaeological sample. Especially important is the useof microscopic methods to evaluate and quantify damage as-sociated with impact, cutting, processing, and other tasks.Obsidian has been shown to be especially prone to accumu-lating clear wear signatures, and application of these methodswill greatly improve our understanding of microlith use in thistime period (see Anderson and Formenti 1996, Aoyama 1993;Conte et al. 2015, Setzer 2012; Stemp and Chung 2011).Linear striation and related micro-wear features have beenshown to be important in evaluating macroscopic fractures

(Geneste and Plisson 1993; Gonzalez-Urquijo and Ibanez-Estevez 1994; Rots and Plisson 2014; Sano 2012; Sano andOba 2015, but see also the more limited application of micro-wear studies in Forssman 2015; Iovita et al. 2014; Pargeter2013; Kufel-Diakowska et al. 2016). We hope that establish-ing a set of testable hypotheses for microlith use within thePastoral Neolithic using macroscopic data will enable futureresearch directed at microscopic analyses and further clarifi-cation of the motivations for microlith use in eastern Africa.

Acknowledgments We would like to thank Scott Johnson, DianaFridberg, and Michael Storozum for their assistance in organizing andconducting the experimental components of this research, and Dr. PurityKiura, Dr. Emmanuel Ndiema, and the staff of the National Museums ofKenya for the permissions to sample these collections and for their vitalassistance in conducting this research (conducted under KenyanNACOSTI permit #14-43161875). We would also like to thank K.Odner, D. Gifford-Gonzalez, G. Isaac, C. Nelson, P. Robertshaw, and F.Marshall, who conducted and reported on the archaeological excavationssampled in this study. Thanks to John Willman, Justin Pargeter, and thecomments by anonymous reviewers, which greatly improved the qualityof this text. This research was funded by the National Science Foundation(Grant BCS-1439123) and Washington University in St. Louis.

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