Raccoon Scavenging and the Taphonomic Effects on Early Human Decomposition and PMI Estimation

Forensic investigators must consider the effects of numerous taphonomic variables when estimating the postmortem interval (PMI) in forensic cases, such as temperature and insect activity. Efforts to quantify the decomposition process have been made. Megyesi et al. (2005) modified the categories and stages of decomposition presented by Galloway et al. (1989), and introduced a total body scoring system that uses accumulated degree-days to estimate PMI. However, none of these systems include the potential effects of animal scavenging. Galloway et al. (1989) stated that carnivorous activity occurs mainly during advanced decomposition and mummification. Haglund et al. (1989) specifically investigated canid scavenging and disarticulation patterns on human remains. Reeves (2009) studied the impact vultures have on human remains and how that information can be useful to forensic investigations. Synstelien (2015) and Jeong et al. (in press) document raccoon scavenging and how their seasonal activity impacts soft tissue decomposition. All of these studies demonstrate that animal activity on human remains may have a significant impact on current PMI estimation methods.

This research investigates raccoon (Procyon lotor) scavenging during the early decomposition stage using daily photographs of ten individuals at University of Tennessee’s Anthropological Research Facility. All of the individuals were scavenged by raccoons. The onset and duration of scavenging was recorded, and then all total body scores and accumulated degree-days (ADD) were calculated using the methods set by Megyesi et al. (2005) to test for accuracy when including this variable in PMI estimation. The results of this research document how raccoon scavenging during fresh and early decomposition impacts estimation of PMI when applying Megyesi et al. (2005) total body scores and ADD calculations by causing accelerated skeletonization and mummification. It also stresses the importance of understanding the numerous variables that can influence the decomposition process (e.g. the relationship between scavenging and increased insect activity) that are not incorporated into current ADD calculations. This research demonstrates the need for understanding the numerous variables, including species-specific modifications, when estimating PMI in a forensic setting.