Prehistoric burned bone

8/13/2019 Prehistoric burned bone

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Samuel Vaneeckhout Juho-Antti Junno Anna-Kaisa Puputti Tiina iks

Prehistoric burned bone: use or refuse

results of a bone combustion experiment

Introduction

In this study we focus on the possible use of bone for fuel and interspecies differencesin bone combustion. The bases for our research are the results of experiments on

bone combustion and of bone mineral density measurements. At the same time this

study provides an opportunity to gain further knowledge on taphonomic factors

affecting prehistoric faunal assemblages. The preservation of the past faunal remains

is an issue of major importance, since the reconstruction of prehistoric subsistence in

Finnish archaeology is usually mainly based on faunal remains from archaeological

excavations. That is based on the assumption that the refuse fauna are the remains of

subsistence and diet1. Other uses of bone, like the use of bone for fuel2, and animal-

derived materials3have received less consideration.

Differential preservation of skeletal parts and its effect on the skeletal

frequencies of a given animal species have received considerable attention within

zooarchaeological research4. Less attention has been given to the interspecies

comparison in bone preservation, although it can considerably change the species

composition of archaeological bone assemblages and affect the interpretation of

1 Ari Siiriinen, On the cultural ecology of the Finnish Stone Age. Suomen Museo88. 1981,540; H. Matiskainen, Studies on the Chronology, Material Culture and Subsistence Economy

of the Finnish Mesolithic, 100006000 b.p. Iskos 8. The archaeological society of Finland,Helsinki 1989; P. Ukkonen, Early in the North Utilization of Animal Resources in Northern

Finland during Prehistory.Iskos 13. The archaeological Society of Finland, Helsinki 2004, 103130.

2 Jarmo Kankaanp, Ihmisi kylmill mailla. Eeva-Liisa Schulz & Christian Carpelan (eds.)

Varhain pohjoisessa. University of Helsinki, Helsinki 1998, 103123.3 Milton Nunez, On the food resources available to man in the Stone Age Finland. Finskt

Museum 97. 1991, 2454.4 P. M. Lubinski, Fish heads, sh heads: an experiment of differential bone preservation in aSalmonid sh.Journal of Archaeological Science23, 175181; M. C. Stiner, On in situ attritionand vertebrate body part proles.Journal of Archaeological Science29, 979991.


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8 S. Vaneeckhout J-A. Junno A-K. Puputti T. iks

past subsistence activities5. In interpretation of Finnish prehistoric animal bone

assemblages, the poorer preservation of sh6and bird bone is usually acknowledged7,

while the dominance of seal in the animal bone assemblages is usually interpreted

as evidence of an economy specialization on seal hunting8. However, we know that

the mineral density of seal bone is generally higher than that of bovids and cervids,

depending on the skeletal part9.

The use of bone as a fuel source is known from historic and ethnographic case

studies. The use of bone as fuel has usually been suggested in relation to wood

scarcity during the Palaeolithic10and at northern latitudes11. Storage of bones seems

to have been crucial in this context12.

Experiments on the use of bones as fuel are limited. The main of the previous

experimental work on bone combustion concentrated on nding the criteria to

distinguish whether bone was burned and to evaluate the burning temperature13.

5 R. Lee Lyman, Bone density and differential survivorship of fossil classes. Journal ofAnthropological Archaeology3, 1984; L. A. Kreutzer, Bison and deer bone mineral densities:comparisons and implications for the interpretation of archaeological faunas. Journal of

Archaeological Science19, 1992.

6 A. Wheeler & A.K.G. Jones,Fishes. Cambridge University Press, Cambridge 1989.7 K. Mannermaa, Birds in Finnish Prehistory. Fennoscandia archaeologicaXX. 2003, 329;

M. Nunez & J. Okkonen, Environmental Background for the Rise and Fall of Villages and

Megastructures in North Ostrobothnia 40002000 cal BC. Dig it all. Papers dedicated to AriSiiriinen. Gummerus Kirjapaino Oy, Jyvskyl 1999, 105116; Milton Nunez, Role of food

production in Stone Age Finland. Paul Fogelberg (ed.) Pohjan poluilla. Suomalaisten juuretnykytutkimuksen mukaan. Bidrag till knnedom av Finlands natur och folk153. Helsinki 1999,133141.

8 J. Ylimaunu,Itmeren hylkeenpyyntikulttuurit ja ihminen-hylje-suhde. Suomalaisen KirjallisuudenSeura, Helsinki 2000; Ukkonen 2004; S. Seitsonen, Osteological material from the Stone Age

and Early Metal Period sites in Karelian Isthmus and Ladoga Karelia. Mika Lavento (ed.)

Karelian Isthmus Stone Age Studies in 19982003.Iskos 16. Helsinki 2008, 265283.9 R. Lee Lyman, Vertebrate taphonomy.Cambridge University Press, Cambridge 1994.10 I. Thry-Parisot, Fuel Management (Bone and Wood) During the Lower Aurignacian in the

Pataud Rock Shelter (Lower Palaeolithic, Les Eyzies de Tayac, Dordogne, France). Contribution

of Experimentation. Journal of Archaeological Science 29, 2002, 14151421; S. Schiegl, P.Goldberg, H. U. Pfretzschner & N. Conard, Paleolithic Burnt Bone Horizons from the Swabian

Jura: Distinguishing between In Situ Fireplaces and Dumping Areas. Geoarchaeology: aninternational journal18 (5).2003, 541565; L. Niven, From carcass to cave: Large mammalexploitation during the Aurignacian at Vogelherd, Germany. Journal of Human Evolution53.2007, 362382.

11 J. F. Hoffecker, A prehistory of the north: human settlement of the higher latitudes. Rutgers

University Press 2005; M. Glazewski, Experiments in Bone Burning. Oshkosh scholar1. 2006,1725.12 Schiegl et al. 2003; Niven 2007.13 For an overview Thry-Parisot 2001.


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9Prehistoric burned bone: use or refuse results of a bone combustion...

An experiment carried out by Thry-Parisot14 showed how bone can be used

to increase the combustion time of res. After conducting several experiments

Glazewski15came to the conclusion that bone could have been used as a fuel source

especially in the Arctic. Fire can be started with grasses and fresh bones can be added

once the re is producing enough energy. A crucial aspect in this case would have

been the drying of the bones of different species or of different body parts to make

them more burnable.

Materials and methods

In this paper we will discuss the possible use of bone as fuel during Finnish prehis-tory based on bone combustion experiments and bone mineral density analysis. The

combustion experiments were carried out to see if bone could have been used as fuel

during prehistory and if there are inter-species differences in burning capacity.

A potential factor explaining the interspecies differences in bone combustion

and post-occupational preservation of burned bones is bone mineral density (BMD).

High mineral content could reduce the amount of carbon based compounds in bone,

slow down burning effects and improve preservation. We also had the assumption

that bone mineral density can alternate during the burning process. To evaluate this

hypothesis we measured the bone mineral density from non-burned and burnedbone.

Bone combustion experiments

To conduct our bone combustion experiment we collected elk (Alces alces), bear(Ursus arctos) and grey seal (Phoca hispida) bones from respectively a huntingassociation, a meat factory and from local shers. Beaver (Castor ber), Forest

Reindeer (Rangifer tarandus fennicus) and harp seal (Halichoerus grypus) were notincluded in the combustion experiment because of non-availability. All bones werefresh and unbroken. For wood we used dried pine and birch wood from one and the

same lot.

We prepared seven experimental res with different contents. One of the

experimental res was made to look at some particular characteristics of bone

combustion and was not a part of the actual experiment. The other six res had a

different content but the same fuel volume, approximately 96 l, and size, measuring

500 mm by 500 mm. To study the effect of different bone/wood ratios on the

14 Thry-Parisot 2001.15 Glazewski 2006.


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temperature, we prepared three experimental res with respectively a 75 % / 25 %,

50 % / 50 % and 25 % / 75 % wood/bone ratios. Interspecies differences were studied

from three experimental res with a 50 % / 50 % wood/bone ratio.

The res were started with birch bark and small pieces of wood. Then wood

was added to get the re burning, once enough heat was produced we added bones

and wood in the same way as fuel. Pictures were taken at the same intervals as the

temperature measurements were carried out. Notes were made about the nature of

the bones and about interesting phenomena which occurred during the combustion

experiment.

Bone Mineral Density analysis

To investigate possible interspecies differences in bone mineral density we performed

density analysis. BMD measurements were taken from elk (n=4), reindeer (n=4),

beaver (n=4), grey seal (n=4), harp seal (n=2) and bear (n=4) specimens. The samples

were taken from cooked bones from an animal museum collection. Bone mineral

density was measured using the Stratec pQCT (XCT960A; Norland/Stratec, Fort

Atkinson Pforzheim, USA/Germany). The pQCT scan was performed to the 50 %

point from the distal end of the tibia. Tibial length was measured by the distance

between the most prominent point of the distal head of the intercondyloid eminenceof the proximal head. The bone mineral densities of each pQCT scan were measured

from three manually dened regions of interest (ROI) in the cortical bone area of the

midshaft.

The difference in bone mineral density between burned and fresh bone was

evaluated by performing pQCT scans for various bone samples. These samples

consisted of fresh and burned elk femora. Scans were performed to 50 % and 75 %

points from the distal end of femur and to the narrowest point of the femoral neck.

The aim of the measurements was to evaluate BMD in both cortical and trabecular

bone in both fresh and burned bone.

Results

Bone combustion

The graph in Figure 1 shows some remarkable differences in combustion properties

of res with a different wood/bone ratio. The re with 75 % bone fuel has a very

uctuating temperature. The temperature of the 25 % bone re is more stable than

res with more bones. Temperatures drop with every addition of bones as fuel. The


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Ratio variation

Temperature

Time

Figure 1: Evolution of temperature over time for different bone/wood ratios.

Species variation

Temperature

Time

Figure 2: Evolution of temperature over time for different species.


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re with 50 % bone has a longer combustion time than the re with 25 % bone.

Temperatures are very similar for the 50 % and 25 % bone res.

The re with 50 % bone fuel produced more light than the 25 % bone re. The 75 % bone

re did not produce enough heat to burn the bones properly. So the addition of bone

to res increases combustion time and light production of res, adding too much

bone results in bad combustion.

The interspecies differences in combustion properties are also remarkable. Elk and

bear bones burn very similarly. Their respective curves show a similar temperature

development throughout the combustion process (Figure 2). Seal bones burn worse

than elk and bear bones. Temperatures drop with the addition of seal bones to the

re.

The uctuation in the temperature curves for bear and elk bones are due to the

difference in combustion properties of different body parts. Rib bones and phalanges

burn relatively fast and at a higher temperature compared to long bones and backbone.

Long bones burn slower but at a more stable temperature for a longer time.

There are also some remarkable differences in the combustion properties of wood

and bone. First of all there is the fact that when all the organic material from bones

is burned the mineral part of the bone cools down relatively fast, especially with

free heat conduction. At the same time there is the interesting insulating property

of bone. Once the bear bone re nished burning, the bones were piled neatly. One

hour after the combustion experiment we measured the temperature which was stillover 400 C. The outer layer of bone was almost cold and could be touched without

protection.

A similar situation with the 25 % bone re resulted in a much colder replace.

Thus bone seems to be much better as an insulator than wood.

Bone Mineral Density

BMD analyses demonstrated that there is a slight difference between the fresh andburned samples. In fresh cortical bone samples BMD varied between 12501400 mg/

ccm and in burned cortical bone samples between 12001250 mg/ccm. Trabecular

bone tests failed as burned trabecular bone was mostly too fragile for accurate density

measurements.

Clear interspecies differences were found in bone mineral densities. The lowest

BMD value was found from bear bones (mean=1308,7 mg/ccm) and the highest

value from reindeer bones (mean=1526 mg/ccm). BMD values for beaver, elk, grey

seal and harp seal were somewhat intermediate between those two. In Figure 3, the

most extreme values for each species are left out of the analysis. We can see howreindeer and grey seal are the species with the highest BMD values while bear has the

lowest values. Beaver, elk and harp seal have intermediate values for BMD.


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Figure 3: Distribution (mean and values) of Bone Mineral Density for different species.The numbers on the x-axis correspond with the numbers in the rst column of Table 1.

Species(n) Mean BMD mg/

ccm

Range (min-max)

mg/ccm

1 Alces alces(4) 1379 1292,5-1461,9

2 Rangifer tarandus

fennicus(4)

1507,3 1382,3-1589,6

3 Castor ber(4) 1363,7 1211,1-1474,6

4 Phoca hispida(4) 1461,3 1243,9-1595,6

5 Halichoerus grypus(2) 1450,7 1383,1-1530,7

6 Ursus arctos(4) 1308,7 1221,8-1373,5

Table 1: Bone Mineral Density (BMD): mean and value range for 6 differentspecies.


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PQCT scans revealed that diaphyseal cross sections of beaver and seal specieswere clearly different from other samples. The medullary cavity was basically absent

in most of those specimens (Figure 4).

Discussion

Our conclusions on the combustion characteristics of bone are similar as those from

Thry-Parisot16. Bone can be used in addition to wood as fuel because of its particular

characteristics. Bone increases the combustion time of res. Bone and wood res

burn with a slightly lower temperature but they burn for a longer time than wood

res. Too much bone results in a very unstable replace which does not produce

enough heat to burn all the bone. Bone also produces more light than wood during

its burning process. In prehistoric (northern) environments) bone could have been

used as a light source in dwellings. It would haven been relatively safe as the heat

produced is lower than with only wood as fuel.

Bear and elk bones seem to be more useful as fuel than seal bones. A possible

explanation for this phenomenon is the relatively high bone mineral density of seal

bone and the almost absent medullary cavity in seal bone. Bear and elk bone contain

16 Thry-Parisot 2001

Figure 4: Diaphyseal cross section for mammals discussed in text.


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more fat than seal bone (bone marrow contains 80 % of fat) partly because seal

stores fat under its skin while bear and elk store fat in the yellow bone marrow in

long bones, etc. The mineral density is most likely also an important factor in post-

depositional preservation of bone. It seems fair to assume that sh and bird bones

have an even lower bone mineral density than mammals.

Our experiments demonstrate that the difference in combustion characteristics

and preservation of bones from different species have to be taken into account when

prehistoric refuse faunas are studied. It would also be important also to take in

account the subsistence related technology like at Yli-Ii, Purkajasuo17and the natural

environment of prehistoric sites. Seal bone burns worse than for instance elk and bear

bones. Similarly there is a better preservation of seal bone. These characteristics will

increase the ratio of seal bone in refuse fauna compared to elk, bear, sh and bird

bones.

A factor which intensies the effect of different combustion and preservation

properties of bone is marrow extracting. The relatively high amount of bone marrow

in elk and bear (noticed from diaphyseal cross sections) will increase the probability

that bones will be broken for marrow extraction. Our experiments revealed that

broken bone burns considerably faster than unbroken bone.

Abstract

Finnish prehistoric subsistence is often studied through the refuse fauna, which mainly

consists of burned mammal bones. Most of these studies have provided us with the

conclusion that during the Stone Age, subsistence strategy was based on large scale

seal hunting. We performed a bone combustion experiment to evaluate whether the

percentage of seal bones in prehistoric refuse faunas accurately represent the role of

the seal in past subsistence economy. The results of these combustion experiments

and further bone structural and densitometric analyses clearly demonstrate that the

better preservation of seal bones probably considerably affects its representationin archaeological animal bone assemblages. According to our analyses there are

clear differences between taxons in the burning and preservation capacities of the

long bones. The fact that seal bone does not burn as good, and preserves better than

bear and elk bones, might explain why we do nd more burned seal bones from

archaeological sites.

Language consultant: Andre Costopoulos

17 H.P. Schulz,Purkajasuon ja Purkajasuo/Korvalan kaivaukset. Unpublished excavation report atthe topographical archive of the Finnish National Board of Antiquities, Helsinki 2000.

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Prehistoric burned bone