Rodents as taphonomic agents: bone gnawing by brown rats and gray squirrels

Passive infrared technology was used to film diurnal and nocturnal scavenging behavior of brown rats and gray squirrels at the University of Tennessee's Anthropological Research Facility. This direct documentation demonstrated that brown rats modified fat-laden cancellous bone while gray squirrels generally gnawed the thicker bone cortices only after fats had leached away. A case study placed in a shaded portion of the Facility indicated the postmortem interval for initial gnawing by gray squirrels was slightly over 30 months. An examination of 53 human skeletons in the William M. Bass Forensic Skeletal Collection revealed that 10 cases had gnaw marks consistent with those made by gray squirrels. One of the 10 cases had been gnawed within 16 months of time-since-death, while the remaining nine had postmortem intervals >30 months. Additional observed modifications made to nonhuman bone by gray squirrels indicate that squirrel gnaw marks on bone can serve as a minimal estimate of time-since-death in a temperate environment similar to that of East Tennessee.     

The formation of early stage adipocere in submerged remains: a preliminary experimental study

In some circumstances, the presence of adipocere may retard decomposition and complicate postmortem interval estimation. This article explores the correlation between Accumulated Degree Days (ADD) and early stage formation of adipocere. Sixty wild rabbit (Oryctolagus cuniculus) carcasses were used in this experiment; a control group (N = 30) deposited directly on the ground surface and an experimental group (N = 30) completely submersed in water in individual buckets. Data (water and inner body temperature, pH, and total body score) were collected every 100 ADD. Results indicated that early stage adipocere is correlated to ADD and that its formation on submersed remains is more likely to occur after 630 ADD. Skin sloughing promoted the formation of adipocere. No adipocere was formed on any of the control group rabbits. This study also highlights the fact that multiple factors influence adipocere formation and it is suggested that further research needs to be conducted into this area.     

Differential decomposition patterns in charred versus un-charred remains

Although researchers have examined many aspects of fire modification, the rate and pattern of decomposition in charred remains have not been studied previously. This study utilized 48 domestic pigs, divided into 24 charred (head, neck, and limbs burned to Crow-Glassman level 1 and torso to level 2) and 24 un-charred pig carcasses. Decomposition of control carcasses was scored at 50 accumulated degree days (ADD) intervals, and charred carcasses were also observed and photographed at this time. A Charred Body Scale was subsequently created, and charred carcasses were scored retrospectively for the same ADD intervals. Analysis using a mixed-effect repeated measures model indicated that, while decomposition rate was not statistically different between the two groups (p = 0.2692), the charred remains initially displayed an ostensibly more advanced pattern. Body regions displaying significant charring decomposed at a faster rate (p < 0.001), while areas with very light levels of charring decomposed at a significantly slower rate (p < 0.001).     

Taphonomic Effects of Vulture Scavenging*

Abstract: From July through September 2007, three pig carcasses (Sus scrofa), weighing between 27 and 63 kg were placed outside in a grassy area in central Texas. A surrounding fence prevented entrance by terrestrial scavengers, while allowing avian scavengers unrestricted access. A fourth pig carcass served as a control for the rate of decomposition and was placed in a cage that prevented terrestrial and avian animal access. Modification of the carcasses was recorded through the use of two motion‐sensing digital cameras and daily on‐site observations. American black vultures (Coragyps atratus) and turkey vultures (Cathartes aura) waited c. 24 h before beginning to scavenge and completely skeletonized the carcasses in 3 to 27 h of feeding, leaving scratches on the bones. The accelerated rate of decomposition and the signature markings on the bones should be considered when interpreting taphonomic events and determining an accurate postmortem interval at vulture‐modified scenes.     

The potential to determine a postmortem submersion interval based on algal/diatom diversity on decomposing mammalian carcasses in brackish ponds in Delaware

Recently botanical evidence has been studied to determine if it is useful in forensic investigations. This study was performed to examine stillborn piglet decomposition in a brackish water environment and to semi-quantitatively document stages of decomposition, degree day accumulation per stage as well as the algal/diatom diversity useful in determining a postmortem submersion interval (PMSI). Piglets and ceramic tiles were submerged in brackish ponds and sampled on a regular basis to document algal diversity and succession between substrates and stages of decomposition. Significantly greater weight was lost from piglet carcasses during the early floating and advanced floating decay stages. Seasonal effects were observed in degree-day accumulations. Diatom diversity was significantly greater on piglet carcasses compared to tile substrates. Algal diversity decreased over time on the piglet carcasses as well as the stage of decomposition. A significant relationship and strong correlation between algal diversity found on the piglet substrate with time was observed. Our results indicate that more research is needed to examine the potential to use diatoms in not only determining manner of death but also the duration of time (PMSI) a victim may have been immersed in an aquatic environment.     

The Effects of Soil Environment on Postmortem Interval: A Macroscopic Analysis

Abstract:  Burial environment, in particular soil moisture, has a significant impact on the type, rate, and extent of bone degradation, which ultimately affects estimations of the postmortem interval (PMI). The purpose of this research is to determine the effects of soil moisture on the color, weight, condition, and texture of bone as it relates to the PMI. Bone changes occurring over two different time intervals (2 and 5 months) were examined using 120 sus scrofa leg bones. During each time interval bones were buried in two soil environments, one of which was drier than the other. The bones in both environments lost weight over time but the net weight loss was greater for bones in the higher moisture environment. There was no change in color, texture, or overall condition, indicating that 150 days is not long enough for such alterations to occur, regardless of the moisture level of the burial environment.     

Internal Morphological Analysis for Age Estimation of Blow Fly Pupae (Diptera: Calliphoridae) in Postmortem Interval Estimation*

Abstract: Larvae and pupae of blow fly species are frequently used in postmortem interval estimation, their age indicating minimum time since death. Most studies have considered age estimation of larvae, neglecting study of pupae. Relative development of external pupal features is useful, but there are also internal changes during metamorphosis that may be indicators of age, utilizing histological techniques. This study aimed to optimize preservation and histological analysis of blow fly pupae, specifically Calliphora vicina Robineau‐Desvoidy and Lucilia sericata (Meigen), and to examine internal features with potential for age estimation. Effect of hot‐water‐killing and different preservatives were examined. It was determined that blow fly pupae should be pierced through the three tagma, hot‐water‐killed, and preserved in 80% ethanol as the optimal preservation for subsequent analyses. Hematoxylin and eosin stained pupal sections revealed differences in brain and thoracic muscle development throughout the pupal stage with potential for age estimation.