Patterns of epiphyseal union and their use in the detection and sorting of commingled remains

Abstract

The utility of epiphyseal union as a means of estimating the age of juvenile remains is well known and documented. Less thoroughly investigated, however equally valuable, is the application of epiphyseal union in the recognition and sorting of commingled remains (Buikstra et al. 1984; L?Abbe 2005; Owsley et al. 1995; Schaefer and Black 2007). Detection of commingled remains is most easily accomplished through the recognition of duplicate elements within an assemblage, i.e., two left femora. In the absence of repeated elements, however, commingling episodes are more difficult to recognize and rely on the anthropologist to detect discrepancies between skeletal elements within the assemblage. Inconsistencies often include variations in size and shape of bilateral elements, disproportionate upper and lower body measurements, or discrepancies in the age, sex, or racial attributes of materials within the assemblage (Buikstra et al. 1984; Byrd and Adams 2003; L?Abbe 2005; Owsley et al. 1995; Snow 1948; Snow and Folk 1970). In much the same way, status of epiphyseal union can serve as a tool to recognize incongruities in the maturity level of different elements. This technique is useful for identifying commingling episodes between juvenile remains mixed with that of either additional juvenile or adult material. While discrepancies between juvenile and adult material may seem obvious, they are less conspicuous if the juvenile skeleton has approximated full maturity, and many epiphyseal elements would be expected to display complete union. The ability to detect discrepancies in the developmental status of juvenile material nearing maturity requires an understanding of the association between union phases of different epiphyses. Three lines of evidence can be used to guide this understanding: (1) the sequence in which the epiphyses initiate union; (2) the sequence in which the epiphyses complete union; and (3) an understanding of the epiphyses that complete union before other epiphyses begin union. Sequences of ?beginning? and ?complete? union have been previously documented by Schaefer and Black (2007), while the relationship between beginning and complete union will be formally examined within this chapter. Once phase associations between epiphyses are understood, the documented patterns can serve as a reference from which to recognize potentially incompatible material. Epiphyseal elements that do not conform to the documented patterns are likely to suggest the presence of more than one individual. Once potentially incompatible material is identified, statistical analysis can be used to further support or reject suspicions of commingling. Statistical analysis is useful in that it simultaneously considers all epiphyseal relationships and mathematically considers the number of observations used to define each pattern. Although normally reserved for aging purposes and stature estimation within forensic anthropology (Lucy et al. 1996; Ross and Konigsberg 2002; Schmitt et al. 2002), Bayes? theorem was selected to perform the analysis, as it is an appropriate statistic to use with ordinal data such as epiphyseal scores (Lucy et al. 1996). Bayes? theorem supplies the probabilistic inference that a suspect element originates from the same individual as the other elements within an assemblage based on phases of epiphyseal union. As a further component of this research, the utility at which epiphyseal phase associations can be applied to recognize the presence of developmentally incompatible material was tested on artificially commingled assemblages. In performing a validation study such as this, an understanding of the method?s reliability was learned. This is an important consideration if the technique is to be potentially admissible in a court of law. Satisfaction of the Daubert criteria (U.S. Supreme Court 1993) for admissibility of evidence in a U.S. Federal Court is becoming a growing concern among forensic scientists (Koot et al. 2005; Ritz-Timme et al. 2000; Rogers 2005; Rogers and Allard 2004; Williams and Rogers 2006). This study attempts to improve the technique?s acceptability through a validation of its reliability. Prior to discussion of the commingling test, an explanation of the three areas of epiphyseal documentation will be presented.