Forensic Anthropology is a journal devoted to the advancement of the science and professional development of the fields of forensic anthropology and forensic archaeology. The journal primarily focuses on research, technical advancements, population data, and case studies related to the recovery and analysis of human remains in a forensic context. Topics such as forensic osteology, skeletal biology, and modern human skeletal variation are within the scope of Forensic Anthropology.
Forensic Analysis of Cremains and Cremains Simulants
There have been several cases in recent years involving unscrupulous or fraudulent practices by funeral homes and crematories, including not actually cremating the bodies and then providing families with urns containing material other than ashes. Numerous techniques can be used to differentiate cremated remains (or “cremains”) from materials used to simulate/replace cremains. Here we use analytical approaches commonly used in the disciplines of forensic anthropology and forensic geology to investigate various properties of materials potentially used as cremains simulants to determine which methods can accurately and optimally be used to identify cremains simulants and differentiate them from authentic cremated remains in forensic contexts. Analyses included visual, radiological, X- ray fluorescence (XRF), and X- ray diffraction (XRD). Samples assessed included human and non- human cremains, burned human bone, and a hydroxyapatite standard as “cremains,” as well as concrete mix, bone meal, diatomaceous earth, sand, and volcanic ash as “cremains simulants.” Visually, most cremains simulants differed from cremains based on color, uniformity, and particle size. Radiologically (assessed as radiodensity), concrete mix and sand were similar to cremains, while bone meal and diatomaceous earth were significantly different. Elementally (using XRF), cremains had phosphorus peaks, and the only cremains simulants with phosphorus peaks were bone meal. XRD was able to identify hydroxyapatite as the primary component in the cremains, and no cremains simulants contained hydroxyapatite. None of these analyses is quantitative, and many properties are relative; therefore, if these analyses are performed in forensic cases, known samples should be used as a reference.
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The Influence of Soft Tissue Presence and Sawing Methodology on Saw Mark Analyses
Previous research in saw mark analysis has relied on non-human bone and/or has been conducted on defleshed bones stabilized with a vice during cutting, conditions that do not accurately replicate most forensic dismemberment scenarios. At present, no studies have empirically assessed how soft tissue and sawing methodology affect the presence and expression of saw cut features on complete cuts made in human samples. The present study aims to fill this gap by examining 638 complete cuts produced by an array of saws (n = 15) on fleshed human remains using free-sawing cutting versus defleshed human bones stabilized in a vice. Twelve categorical kerf features and four saw class characteristics (power, tooth shape, tooth set, teeth per inch) were assessed. Fisher’s and Fisher-Freeman-Halton exact tests indicate the following significant results: fleshed/free-sawing samples are more likely to present with entrance shaving, initial shaving, and polishing and less likely to present with breakaway spurs/notches, pull-out striae, tooth hop, and striation uniformity. Logistic regression analyses revealed important interactions between tissue/sawing methodology, saw class characteristics, and the presentation of kerf features, suggesting that saw characteristics do not equally impact these observed sample differences. These results indicate that tissue and sawing methodology may have more of an effect on kerf feature expression for some saws than others, underscoring the complexity of saw mark analysis research. Caution should be used when applying methods and statistics derived from defleshed, viced saw mark research to forensic dismemberment cases, given that tissue and sawing methodology may affect results, at least for some traits.
The Scope of Taphonomy in Forensic Anthropological Case Reports
Forensic taphonomy plays a vital role in forensic anthropological research and casework, aiding in the reconstruction of perimortem and postmortem events at forensic scenes. Standard guidelines have been published by forensic standards bodies; however, there is considerable variety in the ways in which taphonomic interpretations are incorporated into forensic anthropology case reports. This study analyzes survey responses from forensic anthropologists, professionals, and trainees (n = 56) to assess the extent to which forensic taphonomy is currently integrated into forensic anthropological case reports, the methodologies employed, trends in practitioner education, and the most commonly addressed aspects of taphonomy. The responses revealed that most practitioners include forensic taphonomy in their case reports, mainly focusing on postmortem intervals, bone surface modifications, and the effects of taphonomic agents at the scene. These survey results also indicate that the methods used for taphonomic interpretations vary, with many practitioners relying on casework experience and regional reference texts. Formal education in taphonomy was prevalent among survey respondents. Interdisciplinary collaborations with experts from related fields such as entomology, geology, and climate science are relatively uncommon. This study investigates the scope of forensic taphonomy in forensic anthropology case reports from survey responses and highlights the importance of geographic and case-specific applications of forensic taphonomic methods in broader anthropological interpretations.
Test Approaches to Population Affinity/Sex Classification Using Fordisc 3.1
Fordisc 3.1 is the primary quantitative method of estimating population affinity for the biological profile in forensic anthropology. The creators, Drs. Jantz and Ousley, put forth program use guidelines with two different approaches to population affinity estimation: simultaneous estimation with sex using all 13 available reference samples (Approach 1) or using reference samples from only one sex based on a priori sex estimation (Approach 2). Ousley and Jantz (2012) further recommend reducing the reference samples iteratively down to four (four-way) to two groups (two-way) for the final classification. Using cranial data of known demographic individuals (n = 133), this research tested both reference sample selection and reference group reduction approaches, with and without stepwise selection, to set forth recommendations for U.S. forensic casework. For Approach 2, sex was estimated qualitatively using MorphoPASSE and ordinally scored cranial features. Overall accuracy was higher in Approach 1 compared to Approach 2 by 1.5% to 4.5%, depending on group reduction method and use of stepwise selection. This suggests that Fordisc 3.1 should be utilized for simultaneous population affinity/sex estimation, rather than relying solely on qualitative methods for a priori sex estimation. While accuracy rates were similar between the four-way and two-way analyses, the correct population affinity/sex group was more likely to be retained in the final group comparison for misclassified individuals in the four-way analyses. Finally, while stepwise selection did modestly improve accuracy, larger samples are needed to more critically evaluate the impact on individual population affinity/sex subsamples.
Book Review of: Statistics and Probability in Forensic Anthropology
Statistics and Probability in Forensic Anthropology, Petra Obertová, Andrew Stewart, and Cristina Cattaneo (eds.), Academic Press (Elsevier), 2020, Print ISBN: 978-0-12-815764-0; eText ISBN: 978-0-12-815765-7; 418 pages
Buckle Rib Fractures Are More Than a Pleural Surface Phenomenon
In 2004, Love and Symes introduced buckle rib fractures into the anthropological literature, defining them as “a fracture wherein the bone failed at the point of compressive stress before failure at the point of tensile stress.” In the 20+ years since this straightforward definition was introduced, several variations have been presented, including specifying that fractures only occur on the inner or pleural rib surface, leading to possible confusion about what constitutes a buckle rib fracture. We conducted a literature review to explore these differences. All peer-reviewed sources in English mentioning buckle rib fractures and/or citing Love and Symes’s article were investigated to determine whether they define buckle rib fractures and if they specify a loading mechanism and/or affected rib surface. In addition, a case study is presented that demonstrates multiple incomplete fractures on the right ribs, where the outer or cutaneous surface near the sternal end presented a sharp disruption in the normal alignment of the cortical bone surface, while the pleural surface remained intact. The totality of trauma present suggested that the cutaneous surface was in compression while the pleural surface was in tension. This case study thus demonstrates that buckle rib fractures are not only a pleural surface phenomenon. Therefore, practitioners should specify which anatomical surface is affected, notated as pleural or cutaneous buckle rib fracture, to more precisely describe fractures.
Sex Estimation Using Craniometric Data Obtained Through Computed Tomography With a Sample From Gujarat, India
This study investigates the effectiveness of cranial measurements derived from computed tomography (CT) scans for sex estimation in a western Indian population. Using a sample of 300 adult individuals, 10 cranial measurements were analyzed through discriminant function analysis (DFA). Following multivariate testing and model validation, the final classification model achieved 87.0% accuracy on original cases and 84.3% under cross-validation. Cranial base length and maximum cranial breadth were the most predictive variables. These findings support the utility of CT-based morphometric analysis for forensic sex estimation and underscore the importance of population-specific standards in anthropological identification.
Current standardized methods for sex estimation using the cranial bones involve evaluating landmarks and defining them as feminine, neutral, or masculine, if possible. These methods rely on population-specific data to minimize margin of error, and much controversy exists around the reliability based on the significance of the difference between male and female sex. Sex determination is still a vital component of constructing a biological profile in the identification of skeletal remains. Biological anthropology has only recently been diploid in Namibia, and to date, a benchmark for population-specific data to determine sex using qualitative methods has not been established. This study, therefore, aimed to establish qualitative parameters and evaluate the efficiency at which they can be used to accurately determine biological sex in males and females for victim identification. This study concluded that statistically significant differences (p < 0.05) in mean and variance can be observed between male and female (1) gonial angles and (2) mastoid process length. This study also observed that despite the significant difference in measures of central location, a great degree of range overlap is seen in the gonial angle and mastoid process length. This study concluded that by using qualitative measurements and combining evaluations of at least two clear landmarks on the cranium, accurate sex estimation can be completed 68% to 70% of the time. The landmarks were limited to ones clearly displayed and measurable on archived radio-images while considering transferable osteologic measurements.
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Nonhuman Remains from the Winchester Anatomized Site, Massachusetts
The present research examined the nonhuman skeletal remains associated with anatomized human skeletal remains from a burial site in Winchester, Massachusetts. Other sites have indicated the use of animals for anatomical teaching, including remains found at the anatomized sites of Holden Chapel, Point San Jose, Ashmolean Museum, London Hospital Burial, and Medical College of Georgia. The nonhuman assemblage consisted of 1444 nonhuman remains, making up 9.5% of the total identified Winchester Site skeletal assemblage. The nonhuman assemblage had a total minimum number of individuals (MNI) of 40, including invertebrates. The most represented species were dog (Canis familiaris), cat (Felis catus), and brown rat (Rattus norvegicus). The assemblage also included cattle (Bos taurus), pig (Sus scrofa), sheep/goat (Ovis aries/Capra hircus), macaque (Macaca sp.), European rabbit (Oryctolagus cuniculus), chicken (Gallus gallus), turtle (Testudines), and oyster (Crassostrea sp.). Taphonomic effects from the burial included green copper oxide staining, brown soil staining, and adhering plant roots, and sharp-force trauma (sawing) was present on 1.1% of the remains. The identified species were in some cases likely food remains, with macaque, turtle, cat, and dog likely used for comparative anatomy training. Unknown human remains from anatomized sites can come into the medicolegal system through accidental discovery, and forensic anthropologists must be able to determine their origin through a variety of analyses, including the examination of any accompanying nonhuman remains that also may have been used for anatomical training.
Sources of Sharp-Force Trauma of the Winchester Anatomized Site Assemblage, Massachusetts
Sites where anatomized remains (those subjected to dissection and surgical practice, often with a population derived disproportionately from marginalized individuals) were deposited can come under forensic anthropological analysis, as these are often unmarked burials of unknown individuals. One of the most important criteria in identifying the origin of such remains is the presence of sharp-force trauma, including sawing and drilling (trephinations). The present research examined the human remains from the Winchester Anatomized Site in Massachusetts, dated to as early as the 1850s. The sawn assemblage consists of 1365 adult (9.4% of the overall adult assemblage) and 67 juvenile elements (9.3% of the overall juvenile assemblage). Multiple cranial vault portions exhibited evidence of craniotomy, and three crania also had trephinations. Evidence of surgical training in amputations was present in the form of transverse/oblique complete cuts located on the long bones, and 125 sternal segments and 133 rib segments had sawing consistent with accessing the thoracic cavity. The implements utilized on the skeletal remains were consistent with a narrow, flat-bladed saw with 18 teeth per inch (TPI) (7 teeth per cm), conforming to bone saws of the era, and a trephine. The overall sharp-force pattern was consistent with other known anatomized sites in the United States and was inconsistent with modern dismemberments, corroborating the origin of the deposits as a discarded anatomized assemblage.
Taphonomic Changes of the Skeletal Remains from the Winchester Anatomized Site, Massachusetts
The present research examined the taphonomic effects of anatomized human skeletal remains discovered in a burial feature underneath a construction site in a neighborhood house in Winchester, Massachusetts. Artifact association places the burial of these remains as early as the mid-1800s. Taphonomic profiles of buried remains display certain characteristics that can be used to make comparisons to other known burial types, specifically traditional cemetery burials. The effects observed for the taphonomic profile were soil and mineral staining, bone condition and preservation, plant adherence and/or damage, and postmortem damage. It was hypothesized that the skeletal remains would display a different taphonomic profile compared to previously researched profiles of cemetery remains. There is ubiquitous soil staining throughout the sample and postmortem damage on 69.4%, cortical erosion on 15.7%, plant root adherence on 8.3%, and mineral staining on 5.3% of the identified remains. There is abnormal pink staining on 1.0% of the skeletal remains, possibly the result of a historical embalming technique that used mercury. The analysis also supported the hypothesis that the skeletal remains would display a taphonomic profile more consistent with cemetery remains with direct soil contact and secondarily confirmed that the site was likely used as a medical waste site of anatomized remains. The analysis of the Winchester Anatomized Site also confirmed that the remains displayed a taphonomic profile different from coffin cemetery remains, including a lack of coffin wear or cortical exfoliation, or remains that were prepared and used for anatomical teaching.
The Overall Biological Profile of Adult Remains from the Winchester Anatomized Site, Massachusetts
The present research examined the biological profile of an anatomized human skeletal assemblage discovered in Winchester, Massachusetts (Middlesex County), in 2020 during home construction. The analysis included skeletal sex, age, population affinity, and stature of the adult assemblage. Fragmented postcranial bones could not be matched to individuals, so estimations provided a general profile. The Number of Identified Specimens of the adult remains was 14,469, and the Minimum Number of Individuals was 35. The assemblage was predominantly male skeletal sex: 60.5% of pubic symphyses and 58.8% of greater sciatic notches were male. The average age at death was 23 to 45 years. Population affinity estimation was inconclusive due to cranial fragmentation. Living stature point estimates ranged from 58.1 to 69.9 inches (4 feet 10 inches to 5 feet 10 inches). This profile was compared to the 1850 U.S. Census and military data. The Winchester remains had a higher male representation, similar to Massachusetts’ 1850 poorhouses, penitentiaries, jails, and houses of correction, which had more males than females. In contrast, Middlesex County’s general population had more females than males. The age range of the remains was similar to the majority age group in 1850 poorhouses and criminal institutions. The stature interval was similar to the average height of White males in the United States military (63.7 inches). The profile suggests these individuals may have come from nearby cemeteries, poorhouses, or criminal institutions.
Juvenile Remains from the Winchester Anatomized Site, Massachusetts
A large burial assemblage of fragmented human and nonhuman remains and associated artifacts was disturbed during house construction and excavated in Winchester, Massachusetts, USA, in 2020 and was determined to be a deposition site for anatomized remains dating to as early as the 1850s. Due to their overall development, size, and provenience, n = 724 total elements/fragments were classified as juvenile, with a Number of Identified Specimens = 671. The juvenile elements accounted for 4.8% of the total human sample (n = 15,193). Including all unfused bones, the ages estimated for the juvenile/unfused individuals span from 22 prenatal weeks up to a maximum of 19 years. The total Minimum Number of Individuals for human remains from this site is 46: 35 adults (79.5%) and 11 juveniles (seven of fetal age [15.9%], three younger children [2.3%], and one adolescent [2.3%]). The overall proportion of juvenile remains (23.9%) is consistent with similar sites with anatomized remains and indicates that the remains of young individuals were routinely utilized in anatomical training during the late nineteenth century in the United States.
Excavation, Archaeological Context, and Historical Background of the Nineteenth-Century Winchester Anatomized Site, Massachusetts
In November 2020, an unmarked deposit of mostly disarticulated human remains was accidentally uncovered and partially dispersed by heavy machinery during house foundation excavation in Winchester, Massachusetts, United States. An excavation of the deposit was carried out by the Massachusetts Historical Commission and the Office of the Chief Medical Examiner, with participation by interns from the Boston University School of Medicine, Forensic Anthropology Program. The deposit was in a square feature, 2.0 m north–south, 2.1 m east–west, and ~2.0 m below the former ground surface, and it contained a Minimum Number of Individuals of 35 adult humans, 11 juvenile humans, and 40 nonhuman specimens, along with laboratory ware and ceramics dating the deposit to as early as the 1850s. This deposit is most consistent with former anatomical and surgical training (i.e., “anatomized”) remains, having large amounts of sawing and other sharp-force trauma. To date, the remains cannot be linked to any individual or institution, but they likely derive from a medical or anatomical program in the area. The present article details the excavation of this site, its depositional context, and historical background, with comparison to similar sites.
This study develops nine discriminant functions based on a series of indices calculated on the human pelvic bones from a modern forensic Mexican skeletal population of Maya ancestry from the state of Yucatan. The skeletal collection consists of individuals of known sex and age. Linear measurements were recorded using straight digital and spreading calipers, while the subpubic angle was calculated by means of a 180-degree protractor. Indices that yielded a statistically significant difference between males and females (α = 0.05) were used to calculate discriminant functions, which were then applied to a control sample. Results indicate that the pubic region provides the most reliable estimates of sex, with values ranging between 89.7% and 100.0%. They were followed by the maximum height/ width of the pelvic bone (accuracy of 96.4% and 82.4%, respectively, for males and females) and by the symmetry/asymmetry of the greater sciatic notch (89.7% in males and 88.2% in females). The other indices yielded lower levels of accuracy, ranging between 43.7% and 75.9%. Nonetheless, these less reliable indices are still useful in cases of taphonomically damaged pelvic bones. These discriminant functions are less likely to be affected by subjectivity, individual size, and robusticity and confirm that the male pelvis is narrower and taller than the female one. Compared to qualitative traits, mathematically calculated indices reduce intra-and interobserver error. Last, being developed on a specific population, it will be important to test their applicability to other ethnic groups.
Dr. Turhon A. Murad was the first tenure-track biological anthropologist hired at California State University, Chico (Chico State). He founded the Human Identification Laboratory in 1974, became the 42nd Diplomate of the American Board of Forensic Anthropology in 1989, started the Chico State Certificate in Forensic Identification in 1995, and was active in forensic casework for 40 years. Turhon had a long, successful career as a professor and forensic anthropologist and was influential in the careers and lives of countless students, many of whom became forensic anthropologists. This biography was developed from discussions among the coauthors, all of whom were mentored by Turhon as master’s students. We highlight his key accomplishments, contributions to the field, and the role he played as a mentor and friend. While Turhon sometimes felt like an outsider in the field, given that his academic lineage was outside of forensic anthropology, he was tremendously proud of his students’ accomplishments and the strong program he helped build at Chico State.
Within forensic anthropology, skeletal donations are an indispensable resource for study and research. The creation, collection, and maintenance of skeletal materials have become integral to many anthropology programs, but no protocols specific to forensic anthropology have been established for the management and curation of a donor skeletal collection. Therefore, to assess the need for standardization of body donation in anthropology, two surveys were sent to the greater forensic anthropology community to investigate (a) opinions and (b) practices regarding body donation procedures and use of skeletal remains for teaching and research. There were 105 respondents to the Opinions survey and 36 respondents to the Practices survey. Results of the Opinions survey indicate most respondents agree with the use of donations for teaching and research, but there is disagreement on the ethicality of donation procurement, use, and disposition, especially in cases of unclaimed or unidentified remains. Results of the Practices survey demonstrate the variability in procurement, curation, and use of donors across different programs, including the types of donations accepted, disposition options, forms used for donations, information collected, reasons for not accepting donors, skeletonization practices for fleshed individuals, and the use and consent of donors in imaging, taphonomy, trauma, and other transformative research. Comparing these surveys reveals areas where body donation practices match the opinions of the forensic anthropology community and where improvement is needed. The results from both surveys were used to provide suggestions to aid in the creation of standardized protocols and best practices for body donation in forensic anthropology.
Recognizing Skeletal Presentations of Rotator Cuff and Cruciate Ligament Surgical Interventions
Forensic anthropologists are commonly tasked with assisting investigators in identifying a decedent from an unknown set of human skeletal remains. When traditional methods are not applicable, medically implanted orthopaedic devices have been shown to aid in positive identification. However, not all orthopaedic surgeries result in surgical hardware that can be traced to a manufacturer or individual. This article presents skeletal case examples of two different rotator cuff repairs and an anterior cruciate ligament reconstruction, both of which are common orthopaedic surgeries that do not typically result in traceable hardware. In each case, the repairs were performed 10 years prior, yet the surgical intervention remained identifiable from the bony modifications and suture and screw placements, thereby corroborating decedent identifications. In two of the cases, the remains were burned, and DNA analyses were not possible. In addition to the skeletal presentation of these repairs, anatomical descriptions of the injuries and clinical approaches are provided. The case examples may help forensic anthropologists recognize and interpret similar skeletal modifications in their casework, contributing to identification efforts. Furthermore, these cases highlight the importance of broad anatomical knowledge and exposure to clinical medicine in medicolegal practices.
Quantifying Sexual Dimorphism in Scapular Morphology
This project explores sexual differences in scapular morphology through linear measurements (LMs) and geometric morphometric (GM) methods. Traditional LMs assess size while GM methods primarily assess shape. Our two hypotheses are as follows: the human scapula expresses sexual dimorphism in both size and shape, and given that shape differences exist, this bone will produce higher correct classification rates when assessed for sex using GM rather than using LMs. Three-dimensional data were obtained from the UTK Donated Skeletal Collection (n = 106); linear data were obtained from the Forensic Anthropology Data Bank (n = 1,252). We modeled these data separately to quantify levels of sexual dimorphism in size (LM) and shape (GM) variability. Linear measurements correctly identified 93% of the sample; the GM method could only correctly identify ~70% of the sample when following the GM protocol for the scapular landmark collection outlined in Uhl et al. (2007). However, GM data produced correct classification rates of over 93% when checked for correlation of centroid size. These results indicate that both size and shape drive differences between female and male shoulder girdle morphology, though the primary contributor is sexual size dimorphism. Size-free and/or allometric differences were also noted within this sample but with a much smaller impact on morphology. The human scapula produces high accuracy rates for sex estimation, regardless of whether LMs or GMs are utilized.
Infracranial Epigenetic Variation and the Identification of Unknown Human Skeletal Remains
After a potential match pool has been narrowed using the biological profile, forensic anthropologists often rely on the presence of qualitative skeletal traits for distinguishing between individuals via antemortem–postmortem comparison. This study establishes the epigenetic etiology of several such traits and examines the contribution of the following traits to forensic identification: suprascapular notch, suprascapular foramen, manubrial cleft, manubrial aperture, sternal cleft, sternal aperture, xiphoidal aperture, double-ended xiphoid process, triple-ended xiphoid process, bifid rib, butterfly vertebra, spina bifida occulta, missing transverse process of the first lumbar vertebra (L1), spondylolysis, and sacralization of the fifth lumbar vertebra (L5). Trait frequencies were calculated in totality and according to sex, age, and side occurrence. A sample of 429 (n = 429) individuals were examined from the Bass Donated Skeletal Collection, University of Athens Human Reference Collection, Institute of Forensic Medicine at the University of Zurich, and the New Mexico Decedent Image Database. All traits were determined to be rare (i.e., <10% frequency), except for the suprascapular notch, double-ended xiphoid, and xiphoidal foramen; these traits should not be used for identification purposes. Manubrial aperture, sternal cleft, butterfly vertebrae, and missing transverse processes have the highest utility for identification. Only spondylolysis demonstrated a statistically significant difference between the sexes. Butterfly vertebrae and sacralization of L5 demonstrated a moderate relationship with age. No side or intertrait associations were observed. Consideration of these parameters will allow one to refine the biological profile and provide more accurate conclusions to be drawn regarding trait frequencies in a given population.
Characteristics of Vertebral Body Augmentation in Human Skeletal Remains
Vertebral body compression fractures are extremely common in adults in the United States, particularly postmenopausal women. Vertebral body compression fractures are associated with increased mortality and morbidity and often require medical intervention. Vertebral augmentations such as percutaneous vertebroplasty and kyphoplasty are routinely used to treat vertebral body compression fractures. Here we present two unrelated case studies of willed-body donors exhibiting gross dry bone vertebral augmentations consistent with percutaneous vertebroplasty and kyphoplasty. Vertebrae on both donors exhibit characteristics associated with vertebral body compression fractures, such as decreased vertebral height, as well as protruding areas of a hard, off-white colored substance, which was determined to be bone cement. Additionally, radiographic imaging of the affected vertebrae of both donors exhibits the internal presence of bone cement throughout much of the vertebral bodies. Understanding this medical procedure as well as its morphological characteristics permits forensic anthropologists to correctly recognize these vertebral augmentations and associated abnormalities. Additionally, knowledge of these procedures could assist in the identification process of unknown individuals expressing these characteristics.
Spatial Distributions of Isotope Ratios in Tap Water, Hair, and Teeth from Latin America for Region-of- Origin Predictions of Unidentified Border Crossers
In this article, we present and summarize reference stable isotope data useful in the identification efforts of deceased undocumented border crossers (UBCs) found in southern Arizona and South Texas. In addition, we discuss the use of reference baseline data to refine predictions of region-of-origin of unidentified UBC remains. Overall, Mexican reference hair samples reflect significant consumption of C4 resources, indicating a diet dominated by corn and corn products. Even though meat consumption in the United States is almost twofold that of Mexico, the Mexican δ15N values were elevated over U.S. values, suggesting differences in nitrogen isotope baselines. The comparison of isotope data collected from deceased UBCs recovered from south Texas versus Arizona suggests only small differences in dietary isotopes between the two groups. Geolocation isotopes showed significant differences in δ18O values of both bone and tooth enamel bioapatite, suggesting differences in the sources of drinking water. However, no significant differences were identified between 87Sr/86Sr ratios for the two groups. Further, we present a case application of successful region-of-origin predictions using the δ18O values and 87Sr/86Sr ratios and also discuss some of the inherent limitations and challenges of applying reference data sets to large-scale humanitarian identification projects.
Childhood and Adulthood Residency Prediction Using Strontium (87Sr/86Sr) and Oxygen (δ18O) Isotopes for Unidentified Deceased Migrants Recovered in Southern Texas
Strontium and oxygen isotope values are used in conjunction with a maximum likelihood assignment model to predict the childhood and adulthood geographic residences of 20 deceased migrants recovered along the México-U. S. border in south Texas. The objectives of this research are to determine (1) if the childhood and adulthood residency assignments predict the same geographic region, (2) if using the predicted residential history/nationality as a filter on the National Missing and Unidentified Persons System (NamUs) reduces the number of potential matching missing person reports, and (3) if we should target teeth or bone as the optimal hard tissue to sample. We found that 12 of the 20 cases (60%) predict similar regions of residency using isotopes derived from bone bioapatite (adulthood residency) and tooth bioapatite (childhood residency). When predicted residential history/nationality data were used as a filter in NamUs, there was a significant reduction in the mean number of case searches (mean = 1568.5 ± 505.3 [1 SD] vs. 107.9 ± 142.6 [1 SD]; t = 12.441, df = 22, p < 0.001, unequal variances assumed). These results demonstrate the utility of isotope data for narrowing down the region of origin and in turn the number of missing persons records to review. Finally, we recommend that death investigators at minimum collect dental samples (premolars or molars) for future unidentified migrant cases to aid in identification efforts utilizing isotope analytical methods. Bone bioapatite samples can provide more recent residential history information but should be used in conjunction with tooth enamel data.
Using Real Interpretative Differences to Assess Inter-laboratory Isotopic Variability Due to Sample Preparation
Here we present a two-part study to assess isotope data comparability between two sample preparation laboratories, based on the concept of Real Interpretative Differences (RID). Inter-laboratory isotopic variability should be evaluated prior to compiling data from different sources. Isotopic variability can result from two main causes: sample preparation and sample analysis. We compared the carbon and nitrogen isotope delta (δ) values of 20 modern human bone collagen sample pairs—representing seven individuals from diverse backgrounds—that were prepared close in time at two laboratories and then analyzed at one facility. From this study, values for RID of preparation, or RIDprep, were calculated for bone collagen as 0.43‰ and 0.75‰ for δ13C values and δ15N values, respectively. These RIDprep values were tested using a set of 30 bone collagen sample pairs—representing 30 modern individuals—that were first prepared over a span of five years (2014–2019) at one laboratory; they were prepared again at the second laboratory in 2019. While the differences in isotope δ values between the paired samples in the second study were statistically significant, they did not exceed the calculated RIDprep values for either carbon (30 comparisons) or nitrogen (30 comparisons)—with the exception of one carbon difference in a single paired bone sample. The inherent error rate in combining the isotope test results was thus calculated as 1.7%. This study demonstrated that the isotope data generated from human bone collagen prepared at one laboratory can be reliably compared to data generated from samples prepared at the other laboratory.
Isotopic analyses of human remains augment the biological profile with geolocation and dietary information, furthering efforts to identify unknown individuals from a forensic context. Here we test the methodological resolution of geolocation (δ18O, 87Sr/86Sr) and dietary (δ13C, δ15N) isotopes of one identified individual who immigrated to New York City from St. Vincent and the Grenadines (SVG), Lesser Antilles. Isotope-based geolocation estimates did not identify the childhood residency on SVG, but did point to New York City as a possible residence during early adulthood. The individual’s C3-based diet did not significantly change from childhood to early adulthood, illustrating the maintenance of food traditions after the immigration event. This study illustrates that further development of tissue-specific isoscapes incorporating bioavailable foods, drinking water, and cultural traditions is warranted to refine methodological resolution of isotopic applications in forensic anthropology.
Considerations for Stable Isotope Analysis of Human Hair
Stable isotope analysis of postmortem hair is performed in order to make inferences about an individual’s diet and geographic travel history prior to death. During analysis and interpretation, investigators assume that the hair collected from a postmortem environment has not been altered by exposure conditions and that the isotopic “signatures” of hair prior to exposure are preserved in postmortem samples. In order to confidently make inferences from postmortem hair samples, it is necessary to know whether their isotope ratios undergo postmortem changes. To address this question, post-exposure hair samples (n = 44) were collected from known body donors at the Anthropology Research Facility in Knoxville, Tennessee, USA, at various time points ranging from 22 to 1,140 days of exposure. These samples were analyzed for carbon (δ13C), nitrogen (δ15N), hydrogen (δ2H), and oxygen (δ18O) isotope ratios, and the results were compared with pre-exposure hair samples collected from the same donors. This study highlights considerations for the interpretation of isotope ratios obtained from postmortem hair samples in forensic contexts. The results indicate that δ13C, δ15N, and δ18O values from human hair remain relatively consistent over periods up to three years of outdoor exposure, while δ2H values changed significantly between pre-and post-exposure hair samples.
Calculation and Interpretation of Inter-laboratory Variation in Isotope Delta (δ) Values Using Real Interpretative Differences
Building on applications in anthropology, the use of stable isotope ratio analysis of human bone collagen to investigate an individual’s life history is becoming more commonplace in the forensic science community. Careful consideration of the resultant isotope delta (δ) values, particularly in regard to their accuracy and reliability, is paramount when introducing isotope data into the U.S. court system. In this study, we use a simple framework to calculate real interpretative difference (RID) values for collagen (“col”) and assess isotope data comparability for sample analysis (RIDanalysis) as well as sample preparation/analysis combined (RIDcombined). The RIDcombined values of 0.59‰ for δ13Ccol and 0.91‰ for δ15Ncol are similar to more complex, published calculations of inter-laboratory variability in the stable isotope analysis of skeletal remains, but they are easier to calculate and intuitively elegant. The RIDcombined as well as RIDanalysis values presented here allow users to examine multiple sources of inter-laboratory isotopic variation (preparation, analysis, and both together) in a two-step process whereby a RID value is constructed and then tested. Implementation of this RID approach will provide surety for the legal and research communities in forensic applications of stable isotope ratio analysis.
This special issue of Forensic Anthropology focuses on applications of stable isotope analysis in forensic anthropology and originated from a 2020 American Academy of Forensic Sciences symposium titled “Crossing Borders: International and Multidisciplinary Applications of Isotope Analysis in Forensic Anthropology.” Stable isotope applications are still relatively new in forensic anthropology, and current applications focus on the provenancing (i.e., sourcing) of unidentified human remains, the identification of possible evidence of starvation or undernutrition in potential abuse and neglect cases, and estimations of time since death.
Informative Priors Produce Precision–Accuracy Trade-off in Dental Developmental Age Estimation
Informative priors in Bayesian analyses improve estimates of adult age, but effects in developmental age estimation are unknown. Accounting for residual correlations between developing teeth is supported, but how characteristics of the correlation matrix might affect estimates of age is unknown. Bayesian priors and correlation matrices are systematically tested for their effects on dental developmental age estimates. Nine cumulative probit models were fit to training samples from 880 dental score sets of London dental patients: the full sample, half samples split by sex or ancestry (Bangladeshi or European), and quarter samples split by sex and ancestry. A target sample of dental development scores from computed tomography images in the New Mexico Decedent Image Database was randomly divided into validation (n = 381) and test samples (n = 188) before analysis. All age ranges were 3 to 21 years. Four priors were tested: uniform and kernel densities derived from all-cause mortality, homicides, and NamUs missing persons data. Thirty-six rounds of age estimation were performed using nine correlation matrices from training sample splits and four priors. Correlation matrices with lower variability measures produced higher age interval success rates. Informative priors produced larger residual error and narrower age intervals without a corresponding decrease in success rate relative to the uninformative prior. Model correlation matrices can and should be evaluated for suitability before estimating ages. The choice of an informative or uninformative prior depends on practitioner priorities of age interval precision versus point estimate accuracy. The model discussed here is published as an R package.
Comparison of Visual and Statistical Pair Matching of the Humerus in a Large Assemblage
Determining whether antimeres are consistent with each other is important in estimating the minimum number of individuals in an assemblage, and this is often done with a simple visual comparison. When there are a small number of individuals, this task is generally straightforward and quick. However, as the number of individuals increases, the ability to make visual comparisons of all elements becomes cumbersome. In these cases, osteometric sorting has become a useful tool for creating shortlists of possible antimeres. Shortlists can save time by providing a smaller list of antimeres to visually compare. However, the risk of the true pair being rejected or not being reflected on the shortlist is a concern. Therefore, this study seeks to determine which statistical methods reject true pairs the least often and how these methods compare to visual pair matching. The default statistical parameters set by OsteoSort that utilize the mean of the summed left–right differences (D) performed better than using the mean of the summed absolute left–right differences (| D |). Utilizing specific measurement combinations in osteometric sorting tests, rather than all possible measurements, was only partially more successful. The true pair was excluded or rejected in statistical tests more often than true pairs being missed in a visual pair matching (VPM) study. Therefore, it is recommended to conduct VPM if the time, space, and resources allow.