Stephanie E. Calce, 1 B.Sc. and Tracy L. Rogers, 1 Ph.D. Taphonomic Changes to Blunt Force Trauma: A Preliminary Study à Abstract: This study examines the effects of taphonomic processes on blunt force trauma (BFT) through an experimental study involving pig heads. Of particular concern is the possibility that taphonomic changes can create pseudo-trauma and/or conceal evidence of actual trauma. BFT was inflicted on 10 pig skulls using a hammer. The skulls were subsequently exposed to the environment for 12 months. Seven taphonomic changes were evaluated: the freeze–thaw cycle; rodent gnawing; carnivore scavenging; presence/weight of soil; presence/weight of rain and snow; movement/displacement of bones; and discoloration due to sun bleaching and grass staining. Taphonomic effects varied between cancellous, compact, fresh, and degreased bone. Freezing and thawing, exposure to rain and snow, movement of the skulls, and soil erosion altered and, in some cases disguised, pre-existing trauma. Rodent and carnivore activity did not obliterate evidence of BFT. Recommendations for evaluating BFT on remains affected by taphonomic processes are presented. As each taphonomic process outlined by this study has the potential to disguise antemortem injury, the authors propose that one must carefully examine large, circular openings in the skull that may represent the remnant evidence of BFT. KEYWORDS: forensic science, forensic anthropology, blunt force trauma, taphonomy Taphonomy is the study of processes that affect any organism from the time of death to the time of discovery (1). Taphonomic factors include both natural phenomena (environmental, floral, and faunal) and human interference. After death, taphonomic pro- cesses can alter the appearance of bone to such a degree that fo- rensic investigators may not be able to recognize evidence of criminal activity, e.g., surface remains in fields with tall crops can be inadvertently run over by farm equipment, resulting in crushing and sharp force trauma that may mask preexisting intentionally inflicted wounds. Documenting and experimenting with tapho- nomic variables assists forensic investigators to interpret accur- ately the damage inflicted to bone, in particular, to distinguish antemortem trauma from postmortem damage, and to identify taphonomic changes that have the potential to mask evidence of foul play. The literature contains numerous articles discussing taphonom- ic variables that affect the character of bone, but few publications consider whether it is possible for taphonomic changes to entirely disguise antemortem trauma (1–18). The purpose of this analysis is to determine the degree to which taphonomic processes can conceal blunt force trauma (BFT) through an experimental pilot study using pig (Sus scrofa) heads. This objective was achieved by inflicting BFT on 10 pig skulls and exposing them to natural en- vironmental conditions for 1 year. Seasonal variation is a signif- icant component of taphonomic analysis. Different variables impact the remains to a greater or lesser degree, depending on the time of year and length of exposure. This research evaluates the effects of seven taphonomic factors on the impact site and fractures induced through BFT, including: (1) the freeze–thaw cycle in Southern Ontario, (2) rodent gnawing, (3) carnivore scav- enging, (4) movement by scavengers and displacement of the bones, (5) soil encasement/erosion (6). the presence and weight of rain/snow, and (7) bleaching and vegetation staining. The extent of taphonomic alteration and the characteristic marks indicative of BFT were monitored at several stages of the research period and reevaluated at its conclusion. BFT to the cranial vault can be distinguished from other forms of trauma on the basis of six modifications to the ectocranial surface: (1) inbending and initial fracture formation, (2) inward displacement of bone, (3) radiating fractures in the area of out- bending that initiates at one or more points distant to the impact site, progressing both toward it and in the opposite direction, (4) concentric fractures forming perpendicular to the radiating frac- tures, (5) some depression at the sutures, and (6) knapping or flaking along fracture margins (19–21). Based on blunt force fracture mechanics and documented pat- terns of taphonomy, three expectations were postulated: (1) by the end of the study period, approximately 12 months after exposure, taphonomic processes will obliterate all trace of radiating and concentric fractures, but the depression or inward displacement of bone will remain unaffected, providing the only evidence of pre- existing trauma, (2) taphonomic changes one might expect to see along the injury margins of bone over the course of 1 year include: finely scalloped and serrated edges from scavenging, and cracking and/or flaking of bone due to weathering (2,4,5,12–15), and (3) such taphonomic changes are expected to occur in areas of the body that are exposed, unprotected, and moist, specifically the orbital, nasal, and maxillary margins (2,4,22). Methods and Materials Ten fresh (unfrozen) pig heads (S. scrofa) were obtained from animals destined for consumer use. Each head weighed approxi- mately 12–15 pounds. Each specimen was individually numbered, labeled with a Pig Identification Number (PIN) (1–10), and tagged using wire fastened around the mandible for identification. Ani- mals were selected as human proxies in this study for two reasons: à This work has been presented in part at the Canadian Association for Physical Anthropology (CAPA) Annual Meeting. University of Western Ontario, London, ON, Canada, October 30, 2004. 1 Department of Anthropology, University of Toronto at Mississauga, 3359 Mississauga Road N., Mississauga, ON, Canada L5L 1C6. Received 13 June 2005; and in revised form 6 Oct. 2006; accepted 29 Oct. 2006; published 5 April 2007. 519 Copyright r 2007 by American Academy of Forensic Sciences J Forensic Sci, May 2007, Vol. 52, No. 3 doi:10.1111/j.1556-4029.2007.00405.x Available online at: www.blackwell-synergy.com