Animal bones

From ArchyWiki
Jump to: navigation, search

Discuss the study of animal bones. How do zooarchaeologists study animal bones and what must they consider when studying them?

Ruiha Webster, 10 January 2005

Introduction

Zooarchaeology studies the past interactions between humans and animals by studying the animal remains recovered from archaeological sites. Its goal is to "reconstruct the environment and behaviour of ancient peoples to the extent that animal remains allow". (Klein & Cruz-Uribe 1984, p.1)

Why study animal bones?

A great deal of information can be obtained from zooarchaeological studies and these include those listed below:

  • Hunting and butchery practices - what cut marks are left from the removal of flesh? Was the tool used metal or flint?
  • Seasonal variations - it may be possible to identify a species only available at certain times of the year. This will indicate a season of occupation of a site.
  • Diet and methods of food preservation - by estimating the minimum number of animals among remains and using modern data to suggest the potential food weight of a carcass, it is possible to calculate the nutritional value of a hunted animal. You can then establish the calorific needs of a number of humans and how many may have survived on the site.
  • Trade and economics - the study of a collection of sheep and goat bones from a Roman villa at San Giovanni helped to understand the degree to which the villa’s husbandry economy was integrated into regional systems of animal and animal product exchanges.
  • Animal domestication and farming - evidence of horse riding in the Ukraine was found through a study of surface wear on horse teeth caused by a bit.
  • Climate and environment – the association of animal bones with particular geological deposits was one of the primary methods by which a sequence of glacial and interglacial episodes of the Ice Age was established in the Northern hemisphere. By establishing which species are present and when they occurred data is gathered on the ecology and environment.
  • Social and religious practices – the possession of a species may be restricted according to social strata. For example, in mediaeval times owning some birds of prey was restricted to nobility. For Hebrews of the Old Testament period the only mammals that were allowed to be eaten had cloven hooves and could ruminate. This ideology was expressed in ritual avoidance.

Considerations

Taphonomy attempts to understand how and why bones arrive in archaeological deposits. There are practical problems to understanding this process as a number of variables affect the composition of items an archaeologist retrieves.

"We must be aware that the assemblages we study may have become seriously biased through the process of decay, degradation and disturbance and during the incorporation of the material into the archaeological deposit." (Rackman 1994, p.16)

Hesse (1999) outlined a number of processes that affect the survival of animal bones both before and after burial. ’Thanatic’ processes cover how the animal died. This includes:

  • Non-human predators - was the animal killed by humans or another animal? Greene (2004) notes that animal bones found in caves can be misleading unless you distinguish those brought in by humans from those brought in by other animals.
  • Selective predation - reflected in the relative abundance of the prey at the time of kill.
  • Conditions of accumulation - were there repeated episodes of culling over a long time?
  • Other processes such as old age, disease or starvation.

’Perthotaxic’ factors cover what happens to the carcass. Bones may be destroyed by weathering, gnawing, trampling, butchering or boiled for stock, used as tools, scavenged by other animals or disposed of in rituals. A carcass can be carried off in a flood and deposited when water subsides or bodies may be bogged down in pits or marshes, for example, the tar pits of Rancho Le Brea, USA.

’Taphic’ processes are the mechanical and chemical actions affecting bones after burial. Freeze- thaw cycles, ploughing, burrowing by rodents and chemical reactions all come under this heading. The survival rate of bones and teeth decreases in acidic soil. While in dry soil, or in deposits with no oxygen and little water movement, bones may survive in excellent condition.

’Anataxic’ factors concern the re-exposure of older material to new perthotaxic processes. Erosion is involved, as is archaeology itself. ’Sullegic’ processes are the procedures undertaken by the archaeologist that bias a sample. Excavation methods are covered here. The final processes are ’Trephic’ or curatorial factors, such as sorting finds, recording and labelling, packing and shipping, the quality of reference skeletal collections and the new storage environment of remains, which may cause deterioration.

Davis (1987) describes these factors as those which are beyond our control and those controlled by the archaeologist. Those beyond our control include the modification of the sample before and during fossilization, the subsequent treatment of the carcass by humans or other animals and the effects of soil composition. Those controlled by the archaeologist are associated with the methods of excavation, recovery and study.

Methods and analysis

For a long time bones retrieved during a dig were simply those noticed by the excavators. It was assumed that excavators recovered nearly all identifiable bones of larger mammals and so data for these animals could be used with confidence. A study by Payne (1975) showed that this confidence was unfounded as numerous bones, particularly smaller parts of a skeleton and isolated teeth were lost.

He criticised the inadequate sampling methods used in normal excavations as there was a bias to larger animals and larger parts of a skeleton. A wide range of small animals were present at most sites but excavators missed them. For example, no fish or bird bones were recovered in studies using normal recovery methods. During Payne’s tests, water sieving showed 9 fish species and 14 birds. This additional information gained by knowledge of smaller animals is of great value for considering seasonal occupation of a site and environmental studies.

Payne recommended water sieving but noted it is expensive and time consuming. His answer lied in using sampling trenches with water sieving and finer mesh on progressively smaller amounts of earth. Sampling strategy and amounts sieved with different meshes must be adapted to different requirements of each site. He also stressed the importance of publishing data in full while describing the methods of recovery.

After cleaning and mending, remains need to be identified. This is done on the basis of the size and shape of the bone. To identify specimens you must have experience of archaeological samples and need to consult reference collections of modern bones and finds from other sites. In the absence of a collection then several good reference books exist for comparative purposes.

Identification of bones and teeth of mammals is often easy but distinguishing between closely related species can be difficult. Generally most fragments including an articular surface can be identified to at least family level, and perhaps to genus and species level.

Analysis covers aspects such as sex and age of the animal and its season of death. The relationship of layers and bones within them is fundamental to analysis. The zooarchaeologist must record the archaeological context of each identifiable bone so that levels and areas of the site can be separately analysed then compared with each other.

The approximate age can be estimated from state of ossification of bone structure or eruption of teeth. Upper and lower jaws are the most useful remains as teeth undergo eruption, wear and loss at certain stages of the animal’s development. Various studies have been conducted in this area, for example, methods were developed by Deniz and Payne (Davis, 1987) to give mandibles an age bracket for Anatolian sheep and goats. There are problems with unequal preservation as bones and teeth of young animals are more likely to have been destroyed. So it is usually only possible to give a minimum estimate of the number of young compared to adults.

Sex may be indicated by the presence of antlers or the character of horns, although it is rare for enough of these bones to occur at a dig. Many species will show a difference in size between the sexes so it is possible, from the measurement of particular bones, to define the sex.

The most common statistical measurements of site assemblages are NISP and MNI.

NISP (Number of Identified Specimens) is used to estimate relative abundance of species. This measure is generally misleading, as for example not all mammals have the same number of diagnostic bones, but it is still used as a comparison for older studies.

It is more important to estimate the Minimum Number of Individuals. MNI is generally determined by counting and siding of the most frequent element in an assemblage. For example, 13 tibias suggests 7 individuals but if they are all left tibias that a minimum of 13 individuals are represented. Other useful calculations include MUI (Meat Utility Index) or FUI (Food Utility Index).

Conclusion

The objective of animal bone archaeology is to portray interactions between animals and people in a cultural setting (Hesse & Wapnish, 1999). Zooarchaeologists identify and record animal remains, their frequencies, butchery marks and various species data such as size, sex, age. This is also related to the stratagraphic provenance of the finds. Results are compared with data from other sites and modern bone compilations and comments are made on questions of diet and environment, animal evolution and what their useful products may have been. Questions may also consider how animals were thought of by the people who interacted with them. As a final process all results should be published in detail to allow for future comparisons.

References

DAVIS, S.J.M. (1987) The archaeology of animals. B.T.Batsford Ltd, London.

GREENE, K. (2004) Archaeology: an introduction. Routledge. London.

HESSE, B. & WAPNISH, P. (1999) Animal bone archaeology: from objectives to analysis. Taraxacum, Washington.

KLEIN, R.G. & CRUZ-URIBE, K. (1984) The analysis of animal bones from archaeological sites. University of Chicago Press, Chicago.

PAYNE, S. (1975) Partial recovery and sample bias, pp.7-17 In: Archaeozoological Studies: papers of the Archaeozoological Conference 1974, edited by A.T.Clason. North-Holland Publishing Co. Amsterdam.

RACKMAN, J. (1994) Animal bones: interpreting the past. British Museum Press. London.