The Taphonomy of Human and Non-Human Skeletal Remains in Australian Conditions and the Implications for Post-Mortem Interval Research

Abstract

Estimating the post-mortem interval (PMI) for surface-deposited skeletal remains is a vital component of forensic investigation in order to eliminate cases of non-forensic interest and to assist with identification of a victim. The aim of this thesis is twofold: to examine the relationship between visible changes to skeletal remains and post-mortem interval in an Australian setting and to investigate the validity of using non-human bones as proxies for human bones in such studies.

Estimation of the PMI for human skeletal remains is highly problematic and no standardized method has yet been developed. As a rule, past researchers have investigated single factor methods of PMI determination using either human or non-human remains. Despite small gains, researchers’ efforts are derailed by the complex interaction between environmental factors and the remains and the short time periods over which the studies are done. A longitudinal field study was conducted. At a University of Sydney site (Mandemar), south of Sydney, both fleshed and defleshed bones of human, pig and kangaroo limbs placed on the ground surface were examined and compared over a period of six years. The study focused on recording weight loss, bleaching and weathering (cracking, flaking, surface degradation, exposure of trabecular bone) as well as the interaction of environmental factors such as insects, mould and algae. In addition, a comparison of weathering processes during decomposition was made between the disarticulated human elements from the site above and an intact human cadaver placed out for the purposes of this study at the Australian Facility for Taphonomic Experimental Research (AFTER) in western Sydney, NSW. Factors which showed a relationship with PMI were weight loss, the rate of bleaching of exposed bone surfaces over time, the appearance and/or disappearance of moulds and algae, presence of a carrion beetle and a spike in the onset of weathering processes. Such relationships were however different for human and non-human bones. There were pronounced differences between species with human elements losing considerably more weight over time than the pig or kangaroo. This finding supports published opinions by other researchers that the use of animal substitutes in forensic research may not be valid and should be viewed with caution. The decomposition rate of the cadaver at AFTER was considerably slower than the fleshed, disarticulated elements at Mandemar with bleaching, weathering and growth of algae impeded by mummified tissue, occurring at later stages and not as extensive. This may be attributable to the time of year of placement as the cadaver was initially subjected to cooler winter temperatures. This research should add substantially toward understanding time dependent decomposition processes as they occur over several years in an outdoor Australian setting. This research makes a meaningful contribution to the debate regarding the use of animal proxies in forensic taphonomic research. In addition, the results highlight potentially rewarding avenues of investigation facilitating more focused and specific approaches for future studies.