Sunday, January 21, 2007

Death in the stone age update This relates to this post on some recent work done to identify wounds in archaeological samples resulting from projectile point impacts. The paper in question is:
Experimental evidence for lithic projectile injuries: improving identification of an under-recognised phenomenon, Martin J. Smith, Megan B. Brickley and Stephany L. Leach, Journal of Archaeological Science Volume 34, Issue 4 , April 2007, Pages 540-553

Between the Upper Palaeolithic and the spread of metallurgy stone-tipped projectiles were of great importance both for subsistence and as weapons. Whilst finds of embedded projectile points in human and animal bone are not uncommon, identifications of such wounds in the absence of embedded points are rare. Previous experimentation involving archaic projectiles has not examined the effects of stone-tipped projectiles on bone. This paper presents the results of experiments in which samples of animal bone were impacted with flint-tipped arrows. The results demonstrate that positive identifications can be made, both grossly and microscopically, of bony trauma caused by flint projectiles. In addition, flint projectiles are shown to often leave small embedded fragments, which can also be identified microscopically. These results compare well with archaeological examples of suspected ‘arrow wounds’ and the article demonstrates the practical application of this data in identifying such injuries. By facilitating the recognition of projectile trauma these findings will have significance both for the investigation of hunting strategies and levels of conflict amongst early human societies.

They used two methods of testing: Firing archaeological replicas at faunal specimens, and a mechanical impact tester to both control for velocity and angle of impact and also, as they put it, "a ‘failsafe’ should the present authors’ ability to hit the desired targets with the bow prove lacking". Heh.

Couple of observations: One possible problem, they used defleshed bones for their experimental tests. They did cite a few articles that purportedly found that soft tissue presented no difficulty of penetration, but one has to assume tha soft tissue will slow down a projectile and change the velocity at impact with the underlying bone.

Also noted that in around 50% of the cases, fragments remained in the bone even after removal of the point. Often these were not noted macroscopically, so it could be useful when imaging archeological samples in the future where a lack of a projectile point is the case.

They also noted that modern arrows behave quite differently from ancient stone points, the former being designed more for piercing than cutting. Thus, the ancient specimens tend to penetrate bone more deeply, often piercing through it where the modern tips tend to hit the bone and stop. In this way, the ancient ones tend to behave more like modern ballistics, producing penetrating wounds and internal bevelling.

What did they find? I'll cite their entire 'Conclusions' paragraph:
The present study has provided new information regarding several ways in which stone-tipped projectiles interact with bone. The key conclusions of this study are summarised as follows. Firstly, point breakage leaving stone fragments embedded is frequent when archaic projectiles strike bone. Secondly, and perhaps more importantly, this study has established that it is possible to identify bony trauma caused by stone-tipped projectiles even in the absence of embedded projectile fragments. The supposition that stone-tipped projectiles can produce internally bevelled puncture wounds in areas of flat bone has been shown to be correct. However, it has also been shown that such defects may differ in form and area from those produced by modern projectiles. A particular point of interest was the observation that tangential impacts by stone-tipped projectiles may produce incised marks that resemble cut-marks made with stone tools. Finally, the most significant observation made was that all of the above features have the potential to survive in a recognisable state in archaeological material. Application of the signatures discussed may significantly enhance both the number of such projectile wounds which are identified and the degree of confidence with which such identifications are regarded.

They do note that many of these characeristics are not entirely unique to projectile point injuries. Tools can damage bone in a number of contexts including trophy-taking, defleshing for burial purposes, and cannibalism. These will probably result in markedl different marks though, since defleshing and what-not are designed to remove soft flesh and generally occur around specific locations (joints, tendons insertions, etc.).

Another suggestion to take away is that those oberving the bones ought to be trained osteologists, and I would argue forensic anthropologists who are used to working with trauma. Note to any aspiring forensic anthros out there: There are gazillions of specimens in museum basements that haven't been thoroughly examined for these sorts of injuries.