Tuesday, October 02, 2012

Range of bone modifications by human chewing

In this paper it is present an experimental study of bone modifications caused by human chewing ​​during consumption. Traditionally, tooth marks have been attributed to non-human actors. However, ethnoarchaeological as well as previous experimental work has shown that humans can make many modifications during chewing.
Interest in the identification of human tooth marks is now necessarily increasing, with three lines of research:
1)                  The identification of involvement by hominins (with and without technology) in the formation of faunal assemblages (Pickering and Wallis, 1997; Pobiner et al., 2007; White and Toth, 2007).
2)                  The identification of cannibalism, the most reliable evidence for inference of body consumption (Turner II, 1983; White, 1992; Botella et al., 2000; Andrews and Fernández-Jalvo, 2003; Cáceres et al., 2007; White and Toth, 2007; Fernández-Jalvo and Andrews, 2011).
3)                  The resolution of potential problems of equifinality with chewing damage by other taxa (Martínez, 2007; White and Toth, 2007).
Damages made on bones during hominin feeding can be included in a general pattern that can help us to make inferences about non-cultural signatures produced by hominins/humans. This model included:
(i). Humans can produce a range of modifications similar to carnivores.
(ii). The greatest diversity of modifications is found in flat and/or fragile bones, these modifications are: crenulated and saw-toothed edges, longitudinal crackers, peeling and bend ends. Except for crenulated edges, the other damages are scarce between the products of carnivores. Most carnivores destroy ribs and vertebral apophyses partially or totally (Table 13).
(iii). Crenulated edges made by humans have angular notches. 
Examples of experimental human tooth marks

(iv). Peeling done with the combination of oral and manual force is an unquestionable character of activity requiring prehensile hands. The morphology of the fracture is no different to that described by White (1992). In these cases, the incisors are used, as is done by chimpanzees (Pickering, 2002; Saladié, 2009), like clamps to hold the bone and most of the movement is done with one hand. In most cases small pits and scores are found close to the edge of fracture. Crushing and longitudinal fissures are often found associated with peeling. These partnerships allow us to attribute the tooth marks to anthropogenic consumption with certainty.
(v). Longitudinal cracks and crushing are common in flat bones. These modifications are the result of pressure exerted by biting with large occlusal surfaces. The most effective way to break hard materials and plastics is a contact area as small as possible to maximize the strength of the discharge (Strait, 1997). When the bite is exercised with larger surfaces and various points of contact, force is dispersed, resulting in small fractures that develop into cracks. Similarly, it is possible that this type of large surface biting causes those tooth marks where the perimeter is incomplete.
(vi). Furrowing on the epiphyses is usually slight. Scooping-out, although possible is scarce, and does not always leads to the consumption of spongy tissue. The fractures edges not show licking. In the very small size animals such as rabbits may be more common resulting in shaft cylinders.
(vii). Tooth marks (scores, pits and punctures) are also more abundant on flat bones. Humans rarely produce perforations and punctures.
(viii). Pits may be crescent-shaped.
(ix). Some scores show flaking on the edges and bottom of the scores along their length. Others scores exhibit occasionally internal micro-striation.

The results
 The results suggest that the range of damage is as extensive as that most likely to be produced by carnivores. This damage includes furrowing, scooping-out, crenulated and saw-toothed edges, longitudinal cracking, crushing, peeling and tooth marks. In this paper we present a description of the types of damage observed in the experimental sample. Some of this damage shows parallels between the experimental modifications and archaeological assemblages from Pleistocene and Holocene deposits at the Sierra de Atapuerca sites (Burgos, Spain). The repetition of morphologies allowed us to attribute some of the damage to tooth marks made by human chewing.
For further information:
Saladié, P., et al., “Range of bone modifications byhuman chewing”, Journal of Archaeological Science (2012), 
Palmira Saladié