Developing Regional Taphonomic Standards
Marcella H. Sorg
Abstract
The goal of this project was to develop regionally specific standards for taphonomic (postmortem) data collection and interpretation in northern New England, to be used in the recovery and interpretation of human skeletal remains. The objectives included analysis of a 30--year outdoor case series and controlled observational studies of nine pig (Sus scrofa) cadavers to illuminate key components of the model.
Cases in the series had a known postmortem interval under two years. We analyzed case files for taphonomic patterns and calculated the accumulated degree days (ADD) based on the nearest weather station. Most were found in the woods and 69% were scavenged. Scavenging, including defleshing and bone modification, potentially precludes or obscures decomposition, resulting in scattered, incomplete, and damaged remains, which may be unsuited for testing using, e.g, the models of Megyesi et al. (2005) or Vass (2010) to estimate the postmortem interval (PMI). Based on findings from the case series analysis, we proposed components of the northern New England model including high scavenging prevalence, seasonal cold temperatures and snow with restricted insect access, and mostly forested environments. We used geographic information systems and weather station data to analyze environmental characteristics and calculate accumulated degree--days for specific PMIs.
We refined the model using nine pig cadavers as a preliminary validation of the presence of key components of the model using controlled observation. Pigs served as case study examples of patterns seen in the forensic case series, with the added advantage that we could observe some taphonomic sequences throughout the entire postmortem process using infrared cameras, temperature/humidity data loggers and periodic examination. Whereas this approach, combined with the limited number of pig cadavers, does not allow statistical conclusions, it does allow formation of a preliminary model of decomposition processes in this region. From the model presented here hypotheses can be generated and tested in the future.
Major variables included scavenging/no scavenging, death in warm or cold weather, and placement in forest or field. Decomposition, scavenging, and changes in weather were monitored. Microenvironmental context was assessed in terms of botanical, entomological, and geological characteristics.
The high level of scavenging was validated among the unprotected pig cadavers, all of which were scavenged, and new features of scavenging were identified. For example: (a) defleshing did not include bone modification in any of the scavenged animals; (b) deep snow did not prevent scavenging; and (c) multiple species were involved at different decomposition phases. We present a draft protocol to identify defleshing without bone modification. We also provide a video detailing the scavenger guild behaviors during winter scavenging. We have produced a visual decomposition atlas based on the pigs that were protected from scavenging, including both accumulated temperature and temporal benchmarks.
Our research suggests important ways in which forensic cases in northern New England are characteristically different from other regions in access to heat, moisture and scavenging. The proposed Northern New England Taphonomic Complex includes the following key traits: (a) 5--6 months average temperatures below 4°C (40°F) with a corresponding absence of necrophagous insect activity; (b) 75--80% of the land forested; (c) low human population density; (c) precipitation above 127 cm (50 inches) a year; and (d) a high level of scavenger involvement. We propose associated protocols for scene processing.
Results of the research are being utilized in the Maine and New Hampshire criminal justice community. This regional taphonomy information system approach can be adopted in other regions, with the potential of data comparison across regions. A symposium organized for the 2013 American Academy of Forensic Sciences explored patterns found in multiple regions and began the work of comparing patterns.