Internet Archaeol. 13. Roksandic. Skeletal preservation

2 Skeletal preservation

The presence of skeletal remains in archaeological and forensic contexts is the product of interplay of extrinsic factors of burial environment and intrinsic factors of bone structure and shape (Child 1995; Henderson 1987; Waldron 1987a). Extensive literature exists on animal bone preservation (Lyman 1994), while Waldron (1987b) was among the first to draw attention to the need for systematic reporting of preservation of human bones in an archaeological situation. 'Skeletal preservation', as used here, refers to the number of bones and bone fragments representing one individual in the assemblage, while at the level of bone itself we can distinguish two aspects of bone preservation: 1) 'bone presence', or whether or not the bone is present in the assemblage and 2) 'bone preservation' sensu stricto, or to what degree the present bone is altered by natural or cultural factors. Both of these strongly affect the amount of information that can be derived from skeletal remains, and while this is often a limiting factor in inferring the biological profile of the series, under certain conditions both can reveal important information on the burial ritual, since mode of disposal will influence both of these aspects (Roksandic 2002, 101).

2.1 Paleodemography

Skeletal preservation plays a crucial part in reconstructing demographic profiles of past human groups. It is inherently problematic to assume that the number of burials excavated is representative of the number of individuals originally buried in the cemetery, even in cultures where single primary interments predominate; it is obviously impossible in the case of multiple or group burials. Ubelaker (2002, 332) suggests that commingling is a relatively common occurrence in the archaeological record, even when it cannot be ascertained due to the lack of recognisable doubling of elements. Therefore, in most of the archaeological samples, it becomes a crucial first step in analysis to assess the Minimum Number of Individuals (MNI). Once the MNI is determined, preservation plays an important role in selection of methods for sex and age determination. Because of its potential to reduce our ability to assess age – a notoriously difficult task in adult skeletons (Jackes 1992; Jackes 2000) – preservation has to be recorded and discussed in any paleodemographic study. If the requisite parts of the skeleton are not present for age or sex estimation, assessing the population profile becomes even more problematic.

On the other hand, it has been stated that demography itself affects bone preservation, since subadult and female skeletons preserve less well than adult and male skeletons (Weiss 1972). However, experimental studies have not given positive results and there seems to be no correlation between sex and preservation (Henderson 1987; Nawrocki 1995, 45). Some correlation was found with age in adults (Baud and Gossi 1980; Masset 1973), but it is very low and becomes negligible when other factors are in play. Subadult skeletons seem to conform to the pattern of poorer preservation with younger age, although Masset (1987, 115) cautions against too much reliance on this model. Although infant bones generally preserve poorly, the other possible explanation for their absence in the assemblage can be found in the cultural norm, as many cultures practise differential treatment of infants, for example in Classical Greece and Rome (Morris 1992, 14, 18).

2.2 Palaeopathology and population studies

The most important influence 'bone presence' exerts is when different taphonomic factors act by removing critical elements of the skeleton and preventing observation of pathological conditions. Differences arise from a number of reasons, ranging from natural factors – for instance soil conditions, micro and macrofaunal activity, weathering – to diverse cultural factors such as burial ritual, ulterior manipulations of bones by group members, as well as excavation procedures, differential collection, and storage procedures (Duday 1978; Haglund and Sorg 1997; Haglund and Sorg 2002; Haglund et al. 1989; Morris 1992, 18; Roksandic 2001). Waldron (1987b) and Mays (1992) call attention to the fact that bone presence will affect the estimates of disease frequency in past human population. Palaeopathologists have to decide whether frequencies of pathologic lesions should be reported by individual or by skeletal element. The unequal preservation argues for quantifying the pathological condition per element (Judd and Roberts 1999, 232), while taking into account bone presence when comparing patterns of disease can help reduce the bias and make comparisons more accurate (Waldron 1987b). Similarly, bone/element presence will determine whether we can record non-metric traits and measure bones/parts of bones, and will thus affect the analyses of population affinities.

Bone preservation, on the other hand, can act as a confounding factor in diagnosis of pathological conditions by mimicking certain aspects of disease. A whole chapter devoted to pseudopathology, or the way different taphonomic factors affect palaeopathological analysis, is presented in one book on palaeopathology (Aufderheide and Rodriguez-Martin 1998: Part Two, 11-18).

2.3 Mortuary analysis

Cultural factors affecting preservation are numerous: humans through their cultural norms decide not only who gets buried, but also where, when and how. The place and mode of decomposition will not only influence the disposition of the skeleton in the grave, but ultimately its preservation. Taphonomy, in studying both animal carcases and human corpses, aims to understand what happens to the body from the moment of death to the moment of analysis. It comprises the understanding of both preservation and disposition of the remains within the archaeological sequence. Preservation has been extensively studied, much more so than disposition [2], and can reveal both the chemical environment in which the body decomposed, and a lot about the cultural environment in which the death, the disposal and the treatment of the dead took place (Sorg and Haglund 2002). Different mortuary practices may induce differential preservation: while teeth are 'born fossils' and have the best preservation in the body, cremation is most detrimental to erupted teeth as the exposed enamel explodes at high temperatures. Experimental studies have shown that rates of decay are inversely proportional to bone size (Lambert et al. 1985; Von Endt and Ortner 1984). Size of the bone will influence not only bone preservation but also the likelihood that it will be recognised and excavated by archaeologists (Mays 1992). While small carpal and tarsal bones preserve remarkably well because of the ratio of cortical to spongious bone and their cubical shape, in the case of secondary burial they might not be collected and put into the ultimate disposal area with the rest of the skeleton (Duday 1978). Together with the hyoid bone, they are also the most susceptible to pass unrecognised and uncollected during excavations. For example, once burial conditions and the standard of archaeological excavation themselves are accounted for, systematic absence of individual skeletal elements can provide clues for the interpretation of burial ritual. In the case of excellent preservation and thorough retrieval of bones and bone fragments by archaeologists, missing small bones of the hand or foot and other elements that preserve well because of the compact vs. spongious bone ratio, can be used as an argument for secondary burials. However, conclusions based exclusively on the bones presence/absence in the assemblage should be avoided. Careful mapping is needed to provide crucial information on the burial practice. A very good example of a poorly preserved skeleton distributed over a number of ceramic vessels and in the surrounding soil is provided by Saul and Saul (2002, 78). While the first impression is that of a scatter of fragments, or even an offering, careful examination of the position revealed a primary burial. Considering excavation, documentation, and fragment collection techniques, therefore, are the first requirements when discussing cultural action based on bone presence.

[2] 'Disposition' refers to the spatial distribution of skeletal elements at the time of excavation. It is introduced as a term as distinct from 'disposal', which refers to action by members of the community of the deceased that results in specific burial practice or, more accurately, specific mode of disposal (Roksandic 2002)