A Taphonomic Study of Bone Modification and of Tooth-Mark Patterns on Long Limb Bone Portions by Suids

International Journal of OsteoarchaeologyInt. J. Osteoarchaeol. 19: 345–363 (2009)Published online 11 July 2008 in Wiley InterScience

87
(www.interscience.wiley.com) DOI: 10.1002/oa.9
* Correspondence to: DeparComplutense de Madrid, CiuSpain.e-mail: m.dominguez.rodrigo

Copyright # 2008 Joh

A Taphonomic Study of BoneModification and of Tooth-MarkPatterns on Long Limb BonePortions by Suids

S. D. DOMINGUEZ-SOLERA AND M. DOMINGUEZ-RODRIGO*

Departamento de Prehistoria, Universidad Complutense de Madrid, Ciudad Universitaria

s/n, 28040 Madrid, Spain

ABSTRACT This work presents new taphonomic data on bone modification by suids, including domesticpig, wild and hybrid boars. The intense modification undergone by bones from animalssmaller than 100 kg is shown, together with a more moderate modification on bones fromlarger animals. Both the ravaging pattern (with preferential deletion of cancellous tissue) andthe tooth-marking frequencies are similar to those documented among hyenas and dogs whenhaving primary access to complete bones. A dual-patterned experimental model consisting ofthe interaction of humans and suids was also considered. Here it is shown how suidmodification of hammerstone-broken bone assemblages is different from that documentedamong canids and hyaenids, as experimentally replicated. These results increase the numberof non-anthropogenic bone-modifying agents and posit new issues on equifinality processes.Copyright � 2008 John Wiley & Sons, Ltd.

Key words: bone ravaging; tooth marks; suids; actualistic research; taphonomy

Introduction

Extensive taphonomic research on bone modifi-cation by carnivores has been carried out in thepast few decades. Most of the modelling andinterpretations of biotic non-human modificationof bone assemblages have used carnivores,namely hyenas and to a lesser extent canids(Binford, 1981; Brain, 1981; Bunn, 1982; Skinneret al., 1986; Blumenschine, 1988; Kerbis, 1990;Skinner & van Aarde, 1991; Lam, 1992; Mareanet al., 1992; Blumenschine & Marean, 1993;Selvaggio, 1994; Villa & Bartram, 1996; Capaldo,1995, 1998; Brugal et al., 1997; Fosse et al., 1998;

tamento de Prehistoria, Universidaddad Universitaria s/n, 28040 Madrid,

@gmail.com

n Wiley & Sons, Ltd.

Selvaggio & Wilder, 2001; Pickering, 2002;Marean & Cleghorn, 2003; Pickering et al.,2003; Castel, 2004; Marean et al., 2004; Cleghorn& Marean, 2004, 2007; Marra et al., 2004; Villaet al., 2004; Mondini, 2005; Lacruz & Maude,2005; Faith, 2007; Pokines & Kerbis Peterhans,2007). Some more limited research of bonemodification by felids (Brain, 1969, 1981;Domınguez-Rodrigo et al., 2007a,b) and bears(Andrews & Fernandez-Jalvo, 1997; Pinto &Andrews, 2004) has also been carried out.The interaction of carnivores and humans in

the formation and modification of bone assem-blages has also been experimentally replicated.The carnivore–hominid, carnivore–hominid–carnivore and hominid–carnivore interactionswere first experimentally modelled and thenapplied to African Plio-Pleistocene archaeolo-gical sites (see summary in Domınguez-Rodrigo

Received 13 November 2007Revised 5 February 2008

Accepted 26 February 2008

346 S. D. Domınguez-Solera and M. Domınguez-Rodrigo

et al., 2007a). It has been argued that thefrequency of tooth marks on long limb bonemid-shaft fragments is a heuristically powerfulway of differentiating between primary orsecondary access to carcasses by carnivores(secondary access being when hominids havefirst modified the carcass in some way) (Blu-menschine, 1988, 1995; Selvaggio, 1994;Capaldo, 1995, 1997, 1998; Blumenschine &Pobiner, 2006; Pobiner, 2006; Blumenschine et al.,2007). This view has recently been challenged byDomınguez-Rodrigo et al. (2007b).The present study contributes with tapho-

nomic information about a type of bone-modifying agent (suids) neglected in traditionaltaphonomic literature. It will place emphasis ontheir skill to modify bones as well as theirresulting tooth-marking abilities. Greenfield’s(1988) pioneering work on the taphonomy ofomnivore domestic pigs showed that theseanimals could modify bones in a comparableway to more traditional bone-crunching carni-vores like hyenas and dogs. Greenfield (1988)documented that pigs could destroy bonesdifferentially according to carcass size and bonedensity. Most of the bones (90% of MNE,Minimum Number of Elements) from the smalland medium-sized carcasses that he used forexperimentation were almost totally consumedby pigs. Only cattle bones survived. Even in thiscarcass size, pigs showed a proficient skill indeleting cancellous bones, namely vertebrae andsacra. They also inflicted extensive damage toinnominates and long limb bone ends. Greenfield(1988) found that the damage pattern documen-ted in pigs was very similar to that found indog-chewed bone assemblages. This raised thetheoretical possibility that suids might reactsimilarly to hyenas and canids in carnivore–hominid and hominid–carnivore experimentalhypothesis-testing scenarios.Here we will present new experimental data

showing that suids, including wild boars anddomestic pigs, are animals capable of modifyingbones in a very conspicuous manner, supportingGreenfield’s (1988) preliminary findings. Modi-fications of bones by suids could potentially bemistaken for those of other carnivores. It will alsobe shown that suids are even capable ofmodifying and tooth-marking not only complete

Copyright # 2008 John Wiley & Sons, Ltd.

elements, but also hammerstone-broken shaftfragments. The taphonomic implications of thisbehaviour will be discussed in the light of currentactualistic research on carnivore signatures ofbone modification.

Wild boar behaviour and diet

Four species of extant suids are commonlydifferentiated in Eurasia: Sus barbatus, Sus verrucosus,Sus salvanius and Sus scrofa, including up to almost 50subspecies (Saez-Royuela, 1987). Wild boarsoccupy an extensive geographical area and theyare the most widespread form of suid, if thedomestic pig is excluded. In the Iberian peninsula,two subspecies are identified: Sus scrofa scrofa (foundin the north of the country) and Sus scrofa meridionalis(occurring in the south and also in someMediterranean islands) (Rosell et al., 2001).

Wild boars in the Iberian peninsula weigh over100 kg.Males are substantially larger (>20%) thanfemales. They are relatively medium-sized amongsuids. In theCarpathes, for example,wildboars canweigh up to 300 kg. The wild boar permanentdentitionformulais3.1.4.3/3.1.4.3,andmalesgrowtheir canines longer than females. Tusks stopgrowing at 10 or 11 years, coinciding with boars’vitaldecline.During theirgrowth,upperand lowertusks get sharpened due to friction against eachother.Theyareformidableweaponsthatwildboarsuse for defence. Wild boars are short-sighted buthavehighlydeveloped sensesofhearingand smell.Theyareabletodetectfoodupto1munderground.They are opportunistic omnivores. Their diet isbased on plant foods, but a small amount of meatintakeisnecessaryfortheirphysiology(Rosell etal.,2001).Theyconsumeavarieddiet including fruits,grass, stems, roots, bulbs, fungi, lizards, birds,insects and occasional mammal meat. In thePyrenees, their habit of preying on lambs is welldocumented (Herrero Cortes, 2001). Studies withboars in thewild show that inwinter their intake ofprotein is higher than in other seasons; when theyhave been artificially fed on corn, boars spon-taneously seek more animal protein, probably tocompensate for the excess of carbohydrate intake(Schley&Roper,2003).Animalproteinseemstobeanessentialpartofthedietofwildboars,andcannotbe replaced with exclusively vegetarian diets.

Int. J. Osteoarchaeol. 19: 345–363 (2009)DOI: 10.1002/oa

Taphonomic Modifications by Suids 347

HerreroCortes (2001) showed that animal proteinmakes up an average of 10% of the diet energy ofboars,witharangeneverexceeding20%;thisstudyof stomach contents of wild boars in the Aragonregion of Spain showed that micromammalsincluding Apodemus sylvaticus, Microtus duodecimcosta-tus and Crocidura russula occur together withscavenged goat (Capra hircus), the most commonsources of animal protein thatwild boars consume.

Sample and method

A total of 22 experiments (Table 1) – 20 inenclosures (open and closed) and 2 in the wild –were initially designed (18 of which used in thepresent analysis)1 with the aim of documentingthe intensity of ravaging carried out by suids andtheir interest in fleshed and defleshed carcasses.These experiments consisted of providing suidswith different bones and exposing them toravaging for a variable amount of time, usuallyinvolving no more than two hours (excludingexperiments carried out in the wild), since wedocumented that frequently the interest of suidsdeclined after one hour of having access to bones.Experiments were divided according to two mainresearch questions:

(1) F

1Thiauthvisio

Co

or testing suid modification and tooth-markpatterns on complete limb bones (suid-onlymodel) and human–suid interaction in bonemodification on hammerstone-broken longlimb bones (human–suid model), 12 exper-iments were carried out (Tables 1, 2 and 3).Blumenschine’s (1988) pioneering work onhyaenid and human interactions in the modi-fication of bone assemblages was carried outthrough contrasting opposite hypotheses inwhich hyenas alternated in having primary orsecondary access to bones. Here, the sameapproach was followed. We wanted to com-pare how different or similar suids were asbone-modifying agents to other carnivoresthat had been used for identical experimentalscenarios. We made a theoretical assumptionthat suids would modify long bones more

s work presents the results of research conducted by one of theors (SDDS) for his Master’s thesis, conducted under the super-n of the senior author (MDR).

pyright # 2008 John Wiley & Sons, Ltd.

intensively if they were complete than if theywere broken by humans and, as reflected inresults of experiments with hyenas, tooth-marking would be differentially distributedaccording to bone portion in a differentway in each scenario. We designed an experi-mental set aimed at testing the capabilities ofbone modification by suids in a context ofprimary access to fully defleshed completebones (Table 2). A second experimental setwas designed to test the contrasting hypoth-esis of tooth-marking frequency and distri-bution in hammerstone-broken assemblages(Table 3).

(2) S
ome experiments were created with the aimof observing suid ravaging on non-limbelements, including axial skeletons (composedof greasy and soft bones). For this purpose,and in contrast with the previous questionwhere most of the bones were appendicularelements (Figure 1), the bones used for theseexperiments included vertebrae, scapulae andpelves. All bones involved in these experi-ments were either tooth-marked or deleted(see results). No quantitative data beyond thisis provided in this work. Another experimentconsisted of just red deer antler, since it wasassumed that suids could also modify antler, asthey did in our study (the result of this will bepublished elsewhere).
All these experiments were carried out betweenFebruary and September 2007. They were carriedout in several places:

(1) T
he experimental hunting park of ‘El Hos-quillo’ (Cuenca, Spain), managed by the Pro-vincial Delegation of Agriculture andEnvironment in Cuenca. This institution ownstwo wild boars in a special enclosure used forexhibition, as well as several other wild boarsin open spaces.
(2) V
illaconejos de Trabaque farm (Cuenca,Spain). A private farm where domestic pigsare grown.
(3) C
ollados farm (Cuenca, Spain). Also privatelyowned. It contains domestic pigs and a hybridboar.
The experiments involved a 10-year-old femalewild boar (100 kg) and a 2-year-old male wild


Table 1. List of experiments, including type of carcasses and suids used

Number Type� Carcass used Agent

01 1 Lamb 1 adult hybrid male (Collados)02 3 Pig 1 adult hybrid male (Collados)1 1 Lamb 2 adult wild boars (Hosquillo)2 1 Lamb 2 adult wild boars (Hosquillo)3 7 Lamb 2 adult wild boars (Hosquillo)4 1 Lamb 1 young male wild boar (Hosquillo)5 1 Pig 2 subadult pigs (Villaconejos)6 1 Lamb 2 adult pigs and 1 subadult hybrid (Villaconejos)7 2 Pig 2 adult pigs and 1 subadult hybrid (Villaconejos)8 1 Lamb 1 adult hybrid male (Collados)9 1 Lamb 1 adult female pig (Collados)10 3 Lamb 1 adult hybrid male (Collados)11 3 Lamb 1 adult hybrid male (Collados)12 2 Pig 2 adult wild boars (Hosquillo)13 4 Pig 2 adult wild boars (Hosquillo)14 3 Calf 1 adult female pig (Collados)15 2 Calf 1 adult hybrid male (Collados)16 4 Calf 1 adult female pig (Collados)17 5 Red deer 1 adult hybrid male /2 adult wild boars (Collado/Hosquillo)18 7 Pig 2 adult wild boars (Hosquillo)W1 6 Pig Free wild boars (Villar del Saz)W2 6 Sheep Free wild boars (Villar del Saz)

�1, suid-only experiments consisting of one defleshed hindlimb (excluding metapodials and phalanges); 2, human–suidexperiments consisting of one defleshed element (femur); 3, experiments using axial elements (vertebrae plus pelvis);4, fleshed limb elements (excluding metapodials and phalanges; 5, red deer antler; 6, experiments in the wild(W1¼demarrowed limbs of a pig; W2¼partial sheep carcass); 7, experiments conducted using (separately) acombination of meat and plant food. Experiments 5 and 7 will be published elsewhere.


boar (60 kg) from El Hosquillo; a 3-year-oldhybrid suid (mix of domestic pig and wild boar)(130 kg) from Collados farm; another young (lessthan a year) (30 kg) hybrid suid from Villaconejosfarm; and three domestic pigs: a six-year-oldfemale (120 kg) from Collados and 2 yearlings(less than 40 kg) from Villaconejos (Table 1).Each experiment with wild boars was carried outin an open enclosure of a reserve (El Hosquillo,Cuenca, Spain) where wild boars are kept.Experiments with domestic and hybrid pigs werecarried out in an enclosure on a farm (Villaco-nejos and Collados, Cuenca, Spain). In both casesthe enclosures were chosen and arranged so thatthe observation of the process could be fullydocumented under controlled circumstances.These suids do not have animal protein regularlyin their diets. The use of bones for theseexperiments implied introducing alien elementsin their diet. They are regularly fed twice a day.Experiments were carried out without interrupt-ing their regular feeding process, and therefore, ina context of lack of hunger.


Each experiment for the suid-only boneexperimental set focused on bone modificationon defleshed long limb bones. It consisted of anarticulated portion of a hindlimb, usually includ-ing the femur, tibia, patella, astragalus andcalcaneum from lambs and pigs (Table 2;Figure 1). Human–suid experiments involved amore limited set (Table 3).

Bones were disposed articulated (suid only) ordisarticulated (human–suid) depending on theexperiment type. For human–suid experiments,bones were broken on a stone anvil with the aid ofa quartzite cobble hammerstone. Afterwards,marrow was extracted with the fingers. Most ofthe resulting diaphyseal fragments were Bunn’s(1982) Type I (less than 50% of circumferenceshaft).

Suids were observed to stop paying attentionto bones after 1.5 hours. We waited an additional30 minutes and then bones were collected andthe enclosures were carefully cleaned and sievedto recover all the small bone fragments. Boneswere then boiled in a solution of neutral


Table

2.Suid-only

experiments

withdefleshedcomplete

limbbones

No.

Carcass

used

Agent

Numberof

epiphysis

Numberofdiaphysis

Fragments

withtooth

marks

Total

time

Original

Final

Original

Final

Epiphysis

Diaphysis

Others

�Total

01

Lamb

1adulthybridmale

(Collados)

412

222(þ

13<

1cm)

2(16.6%)

22(100%)

24(70.5%)

65min

1Lamb

2wild

boars

(Hosquillo)

43

24(þ

2<1cm)

—1(25%)

1(8.3%)

45min

2Lamb

2wild

boars

(Hosquillo)

44

22

—1(50%)

1(9%)

15min

4Lamb

1youngwild

boar(H

osquillo)

49

26(þ

2<1cm)

1(11.1%)

4(66.6%)

3(cal,ast,tar)

8(44.4%)

1night

5Pig

2subadultpigs(Villaconejos)

44

22

3(75%)

2(100%)

1(fib)

6(60%)

95min

6Lamb

2pigs-1hybridboar(Villaconejos)

33

11

2(66.6%)

1(100%)

3(cal,tar,astr)

6(75%)

1night

8Lamb

1adulthybridmale

(Collados)

416

217(þ

8<1cm)

3(18.7%)

14(82.3%)

4(3

ast,fib)

21(63.6%)

50min

9Lamb

1adulthybridfemale

(Collados)

31

213(þ

5<1cm)

1(100%)

12(92.3%)

3(cal,tar,astr)

16(94.1%)

50min

� cal,calcaneum;tar,tarsals;ast,astragalus;fib,fibula.

Table

3.Human–suid

experiments

withhuman-defleshedandhammerstone-brokenlim

bbones

Exp.Carcass

used

Part

Agent

Epiphysealfragments

(after

hammerstone)

Diaphysealfragments

(afterhammerstone)

Fragments

withtooth

marks

Total

time

Original

Final

Original

Final

Epiphysis

Diaphysis

Total

7Pig

1femur

2pigsand1hybridboar

(Villaconejos)

22

10(þ

4<1cm)

10(þ

1<1cm)

2(100%)

9(90%)

11(91.6%)

90min

12

Lamb

1femur

2wild

boars

(Hosquillo)

22

28(þ

21<1cm)

26(þ

18<1cm)

1(50%)

6(23%)

7(25%)

10min

15

Calf

1femur

1hybridboar(C

ollados)

22

14(þ

7<1cm)

9(þ

1<1cm)

2(100%)

9(100%)

11(100%)

60min

W1�

Pig

4lim

bs

4wild

boars

(1adult,3

subadult)

16

25(4

<1cm)

90(þ

55<1cm)

83(þ

52<1cm)

3(12%)

10(12%)

13(12.03%)

Oneweek

� Controlin

this

experimentwasnotastightasin

thepreviousthree(seetext).Forthis

reason,resultsare

treatedseparately

(seeTable

4).



Figure 1. Each single-limb sample for the suid-only experimental set showing the elements that were present beforeand after suid intervention. Bones in black indicate element presence. Bones in white indicate deletion.


detergent, and after drying were inspectedmicroscopically with the aid of hand lenses(�15–20) under strong light to search forinconspicuous marks.Suid bone ravaging was assessed by comparing

the presence/absence of elements before and aftereach experiment and by determining the degreeof bone fragmentation. Bone fragmentation wasdetermined by dividing the resulting bonefragments by the original number of bones atthe start of each experiment. Tooth-mark analysiswas carried out in two ways: by tallying alltooth-marked fragments and by dividing longbones (femur and tibia) into two differentportions (ends and shafts). Given the variabilityof criteria in the identification of near-epiphysealfragments according to each researcher (seeDomınguez-Rodrigo & Barba, 2006), we decidedto use a more unequivocal classification thatlumped all shaft fragments together.


In order to test whether the intensive tooth-marking and bone modification documented inthese experiments with individuals in captivitywas due to the artificial conditions created byliving in an enclosure (such as boredom), twomore experiments were carried out in the wild as acontrol. A group of wild boars was monitored fortwo weeks in a private hunting reserve (Villar delSaz de Navalon, Cuenca) using professionalhunting blinds. These blinds are customarilysituated a minimum of 50 m away from a feedingspot where hunters watch for several consecutivedays; they observe different boars attracted to thefood and select the individual to hunt. Thisprocess is time-consuming since it involvesseveral hours a day of vigilance and observation.The food left in these feeding spots usuallyconsists of corn and fruit. These wild boars aretherefore not used to consuming animal proteinin these spots. Two experiments were made. One



of them consisted of half a sheep carcass(Table 1). This experiment was intended todocument a suid-only pattern of bone modifi-cation in the wild. A second experiment consistedof the long limb bones of a pig previouslyhammerstone-broken and demarrowed. Thisexperiment was intended to compare with theresults from the human–suid experiments under-taken in captivity, given the unexpected resultsobtained.

Figure 2. Three different examples of variability in theintensity of bone ravaging and modification by suids,probably depending on variability of interest and appetite.(A) Experiment 5 with very slight bone modification;(B) experiment 4 showing moderate modification;(C) experiment 8 showing intense modification. This figureis available in colour online at www.interscience.wiley.com/journal/oa.

Results

It is evident that the degree of damage that suidscan inflict on bones depends on the size of thecarcass and the size/age of the suid, as Greenfield(1988) stressed. Bones from lambs and pigs werefrequently highly fragmented, whereas thosefrom the young cow remained unbroken buthighly modified. Bone destruction and modifi-cation also depends on suids’ appetite, bonedestruction being more intensive when they arehungry than when they have been recently fed(Figure 2). Four experiments were carried outusing bones from the axial-pelvic skeleton. Insome cases the axial skeleton (involving lumbarvertebrae and pelvis both of pig and lamb) werecompletely consumed by the suids. Out of 24axial bones used for this set of experiments,remains of only one bone survived. Wild boarsconsumed the others completely. In contrast, thescapula of the cow was modified moderately onthe spine and on the broad portion of the blade(proximal end). The cow humerus was alsoaffected by furrowing on the proximal epiphysis.Damage on the scapulae and humerus is similar tothat reported by Greenfield (1988). Experimentswith fleshed remains showed that after fleshconsumption and in the context of a lack ofhunger, suids may choose to abandon boneseither complete or partially broken.The proximal and distal ends of femora and the

proximal ends of tibiae of pig and lamb remainswere variously affected by tooth-marking andfurrowing. A striking feature is the moderatedeletion of compact tarsal bones. These compactbones were deleted in three out of eight suid-onlyexperiments. This was previously reported onlyfor hyaenids (Capaldo, 1995).

Copyright # 2008 John Wiley & Sons, Ltd. Int. J. Osteoarchaeol. 19: 345–363 (2009)DOI: 10.1002/oa

Table 4. Mean percentages of tooth-marked specimensin relation to the total number of specimens, in suid-onlyand human–suid experimental assemblages, accordingto bone portion: epiphysis (EPI) and mid-shafts (MSH).Analysis of 95% C.I. for sets of experiments are included.They were calculated using the t distribution, where t0�025is the critical value of t, with n�1 degrees of freedom

Epiphyses Shafts Total

Suid-onlyMean % 47.8 76.8 5395% C.I. (17.8–77.8) (54.8–98.8) (28.5–77.5)S.D. 37.3 27.7 30,8No. experiments 8 8 6

Human–suid �

Mean % 83.3 67.6 71,695% C.I. (46.3–100) (17.6–100) (20–100)S.D. 28.9 38.7 40,7No. experiments 3 3 3

Human–suid��

Mean % 65.5 56.2 57,195% C.I. (18–100) (6.2–100) (12.1–100)S.D. 47 50.4 45No. experiments 4 4 4

S.D., standard deviation.�Excluding experiment W1 whose control (and suid inten-sity of ravaging) was different from the experiments per-formed in the enclosures.��Including experiment W1.


In the suid-only experiments, bone fragmenta-tion is also remarkable. Only 35 limb bonessurvived complete deletion out of the 53 elementsoriginally used. A total of 52 epiphysealfragments and 67 shaft fragments make up theNISP (Number of Identifiable Specimens) of thissample. If considering only specimens larger than1 cm, the fragmentation ratio (portion NISP/portionMNE) is 1.7 for epiphyseal fragments and4.5 for shafts, taking into account that severalelements were consumed without leaving anyfragment. This shows preferential deletion ofepiphyseal fragments and a higher representationof shaft fragments resulting from bone breakage.Tooth-marking is also very high when con-

sidering specimens larger than 1 cm (Tables 2and 4; Figure 3). A total of 53% of the sample istooth-marked. Epiphyseal fragments from com-plete bones broken exclusively by suids aretooth-marked at an average of 47.8%, andthe mean for mid-shaft specimens is 76.8%.These frequencies (especially those from mid-shaft specimens) seem to be similar to those


reported for carnivore (hyena)-only experimentalassemblages (Blumenschine, 1988). This isprobably because suids have multi-cusp molars,which seem to be as active in bone breakage aspremolars, in contrast with hyaenids and canids,where premolars have most of the responsibilityfor bone breakage.

A high frequency of end modification was alsodocumented in human–suid experiments Tables 3and 4), where 83% of the epiphyseal specimenswere tooth-marked. However, in contrast withcarnivore (hyena)-only experiments, where hye-nas hardly tooth-mark hammerstone-brokenshafts (Blumenschine, 1988), suids seemed topay more attention to broken shafts (Figure 3).Freshly broken bones still retained a layer ofgrease apparently appealing to suids, whichwould prompt them to take broken shafts intheir mouths, chew them – in several instancesfurther breaking them – and either swallow themor spit them out. As a result, a total of 67.6% ofhammerstone-broken shafts were tooth-marked.This frequency is much higher than thatdocumented for other carnivores in similarexperimental scenarios. Originally, 58 specimenswere generated by hammerstone percussion.After the intervention of suids, only 45 fragmentswere collected due to swallowing of the missingshaft fragments.

It could be argued that this behaviour isexplained by the small size of the carcasses usedfor the experiments. However, it was alsodocumented in the experiment using cow bones.This unexpected result prompted us to conductmore experiments in the wild. It can easily beargued that this high percentage of tooth-markedmid-shafts could be due to ‘boredom chewing’caused by the artificial environment of theenclosures. For this reason, and due to theextremely time-consuming process of conductingexperiments with boars in the wild (see above),only two experiments were conducted, whichgave more support to the results obtained incaptivity. Given that the control protocol was notas strict (i.e. continuous observation of the wholeprocess) as in the previously reported exper-iments, we decided to treat the results of thesetwo experiments in the wild separately. Oneexperiment consisted of long limb bones ofa subadult pig including two humeri, two


Figure 3. Example of shaft fragment showing intense pitting and scoring resulting fromHuman-suid experiment number15. Arrows indicate the areas of most conspicuous tooth-marking. This figure is available in colour online atwww.interscience.wiley.com/journal/oa.


radio-ulnae, two tibiae, one calcaneum, oneastragalus and carpals. The long bones werehammerstone-broken on a stone anvil and 16epiphyseal fragments, 35 diaphyseal fragments>1 cm, and 55 diaphyseal fragments <1 cm wereobtained (see Figure 4). All of them were placedtogether with the hammerstone and anvil andwere observed for six consecutive nights prior tothe arrival of wild boars. The observation of this‘feeding spot’ was discontinuous (half the timeduring the day and half during the night) butthere was constant control of the spot to ensurethat no other agent had intervened: firstly, bysearching the ground for footprints of potentialcarnivores other than wild boars; and secondly,by observing that the bones remained in theoriginal positions in which they were abandoned(see Figure 4). On the sixth night/day, wild boarsfinally came to the feeding spot and chewed onthe bones (Figure 5). They licked on the anvil’ssurface and turned it around. They proceeded tochew on virtually all the bones >1 cm that weredeposited on and around the anvil, especially onshaft specimens. They abandoned most of thebones in the same place, but a few diaphysealspecimens were moved by several metres (seeFigure 4). After they abandoned the feeding


place, careful collection of the bones was carriedout according to a grid system (Figure 6). A totalof 25 epiphyseal fragments were retrieved withonly three showing tooth-marks (12%), althoughnine out of the 16 complete epiphyseal fragmentshad disappeared. Most of the remaining 83diaphyseal fragments had been moved from theiroriginal position (some as much as 4 m away) andwere either chewed or swallowed (wild boarswere observed to have done so), but only 10specimens (12%) bore conspicuous traces oftooth marks.The second experiment consisted of placing

half a sheep carcass on the same feeding spot,after having been thoroughly cleaned. Itremained on the feeding spot for ten days andnights with the wild boars appearing on the sixthand seventh nights. They ate the flesh andchewed the vertebrae and pelvis, disarticulatingthe front left limb and moving it away from thefeeding spot. It was not recovered. Given theresources available, wild boars did not show anyfurther interest in breaking the bones asthoroughly as in other experiments, althoughmost elements were tooth-marked.Both experiments in the wild are relevant

because they show that wild boars in their natural


Figure 4. Photographs show the placement of epiphyses (ground) and shafts (anvil) on the feeding spot in the wild priorto the intervention of wild boars, and the remaining assemblage that was collected after suid modification of bones. Onlya third of epiphyseal bones were retrieved. The grid shows the area that was carefully cleaned and where intensive bonecollection took place, around the anvil and the original bone cluster. Note that several shaft specimens were carried bywild boars several metres away from their original location on the anvil. This figure is available in colour online atwww.interscience.wiley.com/journal/oa.



Figure 5. Four wild boars during part of the process of bonemodification at the feeding place of Villar de Saz deNavalonprivate hunting reserve. This figure is available in colour online at www.interscience.wiley.com/journal/oa.

Figure 6. Gridding of 36 m2 around the anvil containing the feeding spot and the area surrounding it. This figure isavailable in colour online at www.interscience.wiley.com/journal/oa.



Figure 7. Example of distal end of a pig femur with the typical furrowing caused by suid incisors (as shown in thephotograph on the upper right corner of the image). This figure is available in colour online at www.interscience.wiley.com/journal/oa.

Figure 8. Another example of suid tooth-marks created with incisors on a scapular blade. Notice the very broad andshallow scores resulting from the incisor width, with the cross-section of the main tooth score (A). This figure is availablein colour online at www.interscience.wiley.com/journal/oa.



Figure 9. Example of long limb bone end furrowed by hyenas (upper part of the image). Notice the typical furrowingpattern consisting of a series of denticulate scores on the cancellous bone (A). The central part of the image shows anotch with two tooth marks (B,C) also made by hyenas, which are shown magnified below with their U-shapedcross-sections. This figure is available in colour online at www.interscience.wiley.com/journal/oa.


environment are interested in consuming bothflesh and grease, and that they have the potentialto modify bones (Figures 7, 8, 10) – sometimesdifferently from other carnivores (Figure 9) – eventhose that have already been hammerstone-broken. In the latter case, they only seem todo so when the bones have been recently brokenand the suids can still smell the grease ofmedullary surfaces, which is what prompts themto take the bones in their mouths.

Discussion

Suids can modify complete and fragmented bones(Figure 11). They can transform complete bones


from mammals smaller than 50 kg into a smallcollection of shaft fragments and only a fewepiphyseal specimens. They can delete long limbbone ends in the carcass sizes reported in thepresent work in a similar fashion to thatdocumented for canids and hyaenids. In theprocess, most shaft fragments larger than 2 cm aretooth-marked.The capability of modern suids to modify

bones from larger animals seems to be morelimited. However, they conspicuously tooth-mark them, despite their size. One of thedistinctive features of suid tooth-marking isprominent use of the incisors. Flesh is preferen-tially removed by using the incisors rather thanpremolars and molars, in contrast with other


Figure 10. Example of calcaneum with perforation, showing the L-shaped pattern that was observed in other speci-mens. This figure is available in colour online at www.interscience.wiley.com/journal/oa.


carnivores. This generates long, flat tooth scoreson bone surfaces and also a particular way offurrowing, consisting of the flat removal ofspongy tissue, as can be seen in Figure 7 (seealso Figure 2). Sometimes incisor use is notlimited to spongy areas (Figure 8). This contrastswith the typical carnivore patterns of epiphysealfurrowing and tooth-mark cross-sections(Figure 9). Marks generated with the incisorsare broad and shallow when compared withmarks created with premolar and molar cusps.They can also inflict punctures and large pits onbones. The former show a repeated ‘L’-shapedpattern, probably due to premolar morphologyand use (Figure 10).2 Future research will helpelucidate whether this type of mark is typical ofsuids or not.Galdikas (1978) pioneered the description of a

scavenging episode by suids on orangutanremains. Greenfield (1988) noticed the simi-larities in bone modification between suids and

2In the experience of the second author with a large array ofcarnivores, not a single L-shaped mark like the one shown inFigure 8 was observed. Whether this type of tooth mark is typicalof suids or not will depend on replicability. This will be sought afterin the first author’s more extended dissertation.


canids. He documented that suids modify anddestroy bone according to carcass size. He alsonoticed that domestic suids leave very long toothscores on flat bones, such as the scapula, whichdogs do not make. He then went on to apply hisresults to interpretations of bone modifications inprehistoric settlements where suids havetraditionally not been considered a bone-modifying agent.

The results shown here have some bearing onthe debate of bone modification by hominids andcarnivores in Plio-Pleistocene African savannas.Today, the bush pig (Potamochoerus), the foresthog (Hylochoerus) and the warthog (Phacochoerus)are the living remnants of a more diverse suidgroup present during the Plio-Pleistocene (Harris& White, 1979; Harris, 1983). At that time, agreater diversity of significantly larger suidsexisted in Africa: Nyanzachoerus and Notochoerus(from early Pliocene) and Metridiochoerus andKolpochoerus (middle–late Pliocene/early Pleisto-cene). Most of them were larger than extantAfrican species. Their larger size (some of themprobably over 300 kg) would have enabled themto apply greater strength with their jaws andtherefore they may have been able to destroy


Figure 11. Examples of domestic pig and hybrid boar modifying complete bones (A) and hammerstone-fragmentedbones (B), and wild boars breaking bones (C) andmodifying hammerstone-broken specimens. B, chewing on shafts; D,chewing on distal end of femur. This figure is available in colour online at www.interscience.wiley.com/journal/oa.


bones from larger animals more effectively thanmodern suids.Unexpectedly, modern wild boars and pigs

also seem to be able to modify hammerstone-broken long limb bone shafts to a higher degreethan reported for hyenas. The reason for thisbehaviour probably lies in their appetite for theremaining grease coating on the medullarysurface of broken shaft specimens.3 We docu-mented this on experimentally broken freshshafts, some still slightly covered in grease ontheir medullary surface after marrow removal. Wedo not know whether this can also be applied todrier specimens or not. It is known that suids areomnivores and that the bulk of their diet is notmeat. However, under situations of food stressthey surely can consume more animal protein andgrease than is usual for them. Wild boars havebeen documented to hunt hares and to scavengeon naturally dead carcasses (Herrero Cortes,

3One of the reviewers also suggested the possibility of suids doingthis to supply their calcium needs.


2001). All this has important implications for thetaphonomy of Plio-Pleistocene archaeologicalsites. Firstly, it raises the possibility that suidsmight have been a bone-modifying agent notcontemplated in taphonomic studies until now.Secondly, it can be argued that in certainsituations (e.g. seasonal stress), suids might haveengaged in the consumption of animal proteinand grease, possibly resulting in modification ofbones from carcasses lying on the landscape andof bones freshly abandoned by hominids. IfPlio-Pleistocene suids behaved as modern wildboars do, it is logical to assume that they mayhave occasionally imprinted tooth-marks onhammerstone-broken shafts (Figure 3), giventheir ability to break and swallow bone fragments.This behaviour, experimentally reproduced in thepresent study, would contradict assertions that ahigh frequency of tooth-marks on long limb boneshafts at archaeological sites would exclusivelyreflect a scavenging behaviour by hominids,following a tooth-marking carcass defleshingagent (Blumenschine, 1995).


Figure 12. Distribution of the 95% CI (confidence intervals) for the frequency of tooth-marked specimens for each boneportion in experimental assemblages. Closed square, epiphyseal fragments; open circle, shaft specimens; star, allspecimens. Human–suid A excludes experiment W1, and human–suid B includes experiment W1.


These results also have consequences for theinterpretation of ravaged bone assemblages inproto-historic sites containing domesticated pigs,until now interpreted as the result of the action ofthe domestic canids living inside settlements.Proto-historic breeds of domestic pigs weresimilar in morphology to wild boars, with onlythe latter being slightly bigger (Morales Munız,1988). In Celtic-Iberian sites is it difficult todifferentiate domestic suids from wild ones(Liesau, 2005). This raises the possibility thatboth types of suids would modify bones similarly,as the present study has shown.This study introduced the bone-breaking and

modifying features of suids, placing them in clearproximity to some of the main carnivores knownto ravage carcasses and destroy bone, like hyenasand dogs. In contrast with these canids, suidsseem to show a more variable behaviourdepending on factors that we did not controlfor (i.e. lack of hunger, and continuous or


discontinuous feeding) (Figure 12, Table 4). Thissuggests that the sample used here would requirefurther experimentation to define more clearlythe boundaries of this variability. However, itsrelevance lies in the data provided, showing thecapability of suids to intensively modify and evendelete bones.

When dealing with small and medium-sizedcarcasses – that is, animals smaller than 100 kg –at archaeological sites, the intervention of suids(when present) in the modification of any givenbone assemblage cannot be ruled out in favourof hyaenids and canids. Suids can be differ-entiated from the latter by less extensivedamage to bones from larger animals. However,as Greenfield (1988) first noted, the damageinflicted by suids to such assemblages is similarto that documented in canids. These resultscontribute to widening the referential frame-works that taphonomists have for bone-modifying agents.



Acknowledgements

Thanks to the Soria family (Collados), Juan Igna-cio Crespo (Villaconejos), David and JavierValenciano (El Hosquillo), Julian Navalon andPablo Arroyo (Villar del Saz) for allowing us toconduct research at their properties, and toVanesa Fernandez and, of course, theDomınguez-Solera family (for help in boilingthe bones in several experiments). We are alsothankful to Jesus Torres, Mariano Luis Serna, JoseLuis Palacios and David Tofino. We thank T.R.Pickering and one anonymous reviewer for theirvery useful suggestions. Thanks to M. Prender-gast for her suggestions and for improving thetext.

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Documents

A Taphonomic Study of Bone Modification and of Tooth-Mark Patterns on Long Limb Bone Portions by Suids