Using Radiocarbon Dating and Paleontological Extraction Techniques in the Analysis of a Human Skull in an Unusual Context
Ubelaker, Douglas, Houck, Max M., Forensic Science Communications
A disarticulated cranium and mandible partially encased in an extremely hard plastic material were discovered in a riverbed in Pennsylvania. Several traditional fossil-preparation methods were used to extract the fragile skull from the plastic. Anthropological analysis of the skull indicated it was a male of African ancestry with an age at death greater than 50 years. To clarify time since death, radiocarbon analysis was conducted. The results were compared using the modern bomb curve. The skull revealed pre-1950 levels of radiocarbon, and thus it was not of recent origin.
On August 1, 1999, a poorly preserved metal bucket was recovered from a river in Lancaster, Pennsylvania. Inside the metal bucket was a smaller, white plastic bucket containing a human skull partially embedded in a gray plastic material. The recovered objects were taken to the local medical examiner to have the skull removed from the plastic matrix and to be analyzed. The medical examiner found the plastic to be very difficult to remove, to the extent that the motor on a bone saw burned out in an attempt to extract the skull. The skull and plastic were then sent to the FBI Laboratory to determine the composition of the matrix and to attempt to extricate and analyze the human remains.
Radiographs revealed a skull with the cranium and mandible disarticulated within the plastic matrix (Figure 1). The disarticulation suggested that the cranium and mandible were most likely skeletonized at the time of their immersion into the liquid plastic. The plastic itself was potentially an important clue. Its chemical composition indicated that it was similar to the plastic used in kitchen countertops, not commonly sold to the public in the quantity that was used to encase the skull.
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The removal of the matrix proved to be quite a challenge. The resources of the Smithsonian Institution's Vertebrate Paleontology Preparation Laboratory were drawn upon to remove the plastic atrix with a pneumatic scribe. Several sessions of intensive, meticulous work with the so-called air scribe, used to separate fossils from their geological matrices, were required to extract the delicate skull from the surrounding plastic (Figures 2 and 3).
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Once separated from their plastic context, the cranium and mandible were examined for geological materials which, if present, might indicate if the remains had been buried prior to submersion in the plastic. No soil, however, was found on either item. The cranium and the mandible were then analyzed for anthropological information.
The bone was well preserved with no soft tissue or hair present. The posterior portion of the left ramus of the mandible and the bones of the right cheek area were missing. These areas did not show obvious signs of recent fracture, but it could not be determined if the damage was peri- or postmortem. However, the coloration of the broken margin of the right zygomatic suggested relatively recent fracture. Numerous teeth were missing both ante- and postmortem.
The general robusticity of the remains, especially the large supraorbital ridges, suggested male sex. Discriminant function analysis of cranial measurements (Ousley and Jantz 1996) also suggested male sex.
The extent of cranial suture closure, antemortem tooth loss, and age-related changes in tooth structure suggested a relatively old age at death. In particular, application of the Lamendin technique (Lamendin et al. 1992; Prince and Ubelaker 2002) for age estimation from characteristics of single rooted teeth to the right maxillary canine indicated an age at death greater than 50 years. This technique produced an age estimate of 60.2 years, plus or minus about eight years. All of the collectively available information for estimating age suggested the remains originated from a mature adult, probably greater than 50 years of age. …