Technical Note: The Forensic Anthropology Society of Europe (FASE) Map of Identified Osteological Collections

What we see is what we touch? Sex estimation on the skull in virtual anthropology

BACKGROUND

The increased use of virtual bone images in forensic anthropology requires a comprehensive study on the observational errors between dry bones and CT reconstructions. Here, we focus on the consistency of nonmetric sex estimation traits on the human skull.

MATERIALS AND METHODS

We scored nine nonmetric traits on dry crania and mandibles (n = 223) of archaeological origin and their CT reconstructions. Additionally, we 3D surface scanned a subsample (n = 50) and repeated our observations. Due to the intricate anatomy of the mental eminence, we split it into two separate traits: the bilateral mental tubercles and the midsagittal mental protuberance. We provide illustrations and descriptions for both these traits.

RESULTS

We obtained supreme consistency values between the CT and 3D surface modalities. The most consistent cranial traits were the glabella and the supraorbital margin, followed by the nuchal crest, zygomatic extension, mental tubercles, mental protuberance, mental eminence, mastoid process and ramus flexure, in descending order. The mental tubercles show higher consistency scores than the mental eminence and the mental protuberance.

DISCUSSION

The increased interchangeability of the virtual modalities with each other as compared to the dry bone modality could be due to the lack of tactility on both the CT and surface scans. Moreover, tactility appears less essential with experience than a precise trait description. Future studies could revolve around the most consistent cranial traits, combining them with pelvic traits from a previous study, to test for accuracy.

The Free State Collection for Anthropological Research (FS-CAR): a new contemporary identified skeletal collection in South Africa

Documented skeletal collections are valuable resources for anthropological studies aimed at reconstruction of the biological profile and examination of osteological trauma and pathology. The Free State Collection for Anthropological Research is a new, contemporary skeletal collection, based in central South Africa that has become available for such studies. This paper aims to provide an overview of the collection to encourage its future use in national and international research. The collection currently contains 64 female and 122 male skeletons of individuals that have died in the Free State province since the year 2000. Black individuals constitute 94.6% of the collection. Age-at-death ranges between 19 and 86 years, with an overall mean of 40 years. Year-of-birth ranges from 1927 to 1991. Tuberculosis (22.6%) and influenza/pneumonia (20.4%) are the most common cause of death for these individuals. Although the current demographic profile of the collection is skewed, new individuals are continuously being added. The collection offers several opportunities for anthropological research. The relatively young age-at-death and contemporary nature of the collection make it a useful tool for validation of existing methods for estimations of components of the biological profile. It can also be used in conjunction with other collections for the development of new methods for age and sex estimation and studies of trauma and disease manifestation of the skeleton.

What we see is what we touch? Sex estimation on the pelvis in virtual anthropology

BACKGROUND

Computed tomography (CT) scans are a convenient means to study 3D reconstructions of bones. However, errors associated with the different nature of the observation, e.g. visual and tactile (on dry bone) versus visual only (on a screen) have not been thoroughly investigated.

MATERIALS AND METHODS

We quantified the errors between modalities for sex estimation protocols of nonmetric (categorical and ordinal) and metric data, using 200 dry pelves of archaeological origin and the CT reconstructions of the same bones. In addition, we 3D surface scanned a subsample of 39 pelves to compare observations with dry bone and CT data. We did not focus on the sex estimation accuracy but solely on the consistency of the scoring, hence, the interchangeability of the modalities.

RESULTS

Metric data yielded the most consistent results. Among the nonmetric protocols, ordinal data performed better than categorical data. We applied a slightly modified description for the trait with the highest errors and grouped the traits according to consistency and availability in good, intermediate, and poor.

DISCUSSION

The investigated modalities were interchangeable as long as the trait definition was not arbitrary. Dry bone (gold standard) performed well, and CT and 3D surface scans performed better. We recommend researchers test their affinity for using virtual modalities. Future studies could use our consistency analysis and combine the best traits, validating their accuracy on various modalities.

Sex estimation using orbital measurements in the Croatian population

The aim of this study was to test the sexual dimorphism of orbital measurements in the Croatian population using multi-slice computed tomography (MSCT) images. We have retrospectively taken 414 head CT scans of adults from Croatian clinical hospitals in Split and Zagreb (214 males and 200 females) with slice thickness < 1 mm and no pathological or traumatic changes that could affect the measurements. DICOM files were imported into Stratovan Checkpoint Software and viewed in 2D and 3D using semi-transparent 3D volume rendering. Eight standard measurements were calculated based on twelve orbital landmarks (six paired). Principal component analysis (PCA) was used to explore sexual and regional differences, and linear discriminant analysis was used to develop sex classification models. The PCA showed separation based on sex and region, and additional analysis demonstrated that females and males in Split and Zagreb differed in four orbital measurements (P ≤ 0.001). Only those measurements that did not show regional differences were further analyzed, and all showed statistically significant sexual dimorphism. The accuracy of univariate functions for sex estimation ranged from 53.43 to 71.88%, and for multivariate function, the accuracy was 73.45%. The orbital measurements of the Croatian population showed restricted forensic significance for sex classification. On the other hand, we have shown that they can have a potential for exploring the inter- and intra-population differences.

Validation of discriminant functions from the rib necks in two Portuguese adult identified populations

Sexual dimorphism is the basis for sex estimation research in skeletal remains, helping the positive identification of individuals in forensic backgrounds. In this regard, it has been proved that the metrical analysis of the costal neck of the first four ribs in Spanish contemporary adult skeletons shows high sexual dimorphism, especially in the first rib. However, the validation of any method developed in identified skeletal collections must be compulsorily reproduced in other skeletonized sets to verify either its potential application in individuals from other locations, or the existence of possible biases associated with inter-population variation. Due to the geographical and socioeconomic proximity between Spain and Portugal, this paper aims to check the utility of the discriminant functions designed by Partido-Navadijo et al. (2021) in the two skeletal collections of the University of Coimbra (Portugal). Results show the utility of these discriminant functions in Portuguese population, with frequencies of cases correctly assigned reaching up to 93.6% in the Coimbra Identified Skeletal Collection (CISC); and up to 92.6% in the 21^st Century Identified Skeletal Collection (CEI/XXI). However, two particularities between the Spanish and Portuguese osteological assemblages can be highlighted: the possible existence of secular changes in relation to the CISC collection (1904-1938); and a reversal in the degree of costal dimorphism, being the third and fourth ribs of the CEI/XXI collection more dimorphic than the first ones.

Development and implementation of forensic anthropology in Swedish forensic practice

This paper presents the ongoing development of forensic anthropology in Sweden. We discuss the background of the discipline, its application, as well as its current and potential development in Swedish forensic practice. Collaboration with osteoarchaeologists in skeletal forensic cases has a long tradition in Sweden. Analyses of skeletal remains are performed ad-hoc, in contrast to analyses of fleshed human remains. While several law enforcement employees are educated in forensic anthropology and/or osteoarchaeology, they are not employed in these fields, and regional variations are evident. Internationally, forensic anthropology has become an autonomous forensic discipline over the past decades, requiring skills beyond mere skeletal analysis. To keep on a par with international standards, it may be time to revisit the concept of forensic anthropology in Sweden. Despite the limited presence of supporting organisational structures and systems, forensic anthropological and hard-tissue-reliant physico-chemical analyses have proven valuable in Swedish forensic practice, especially in cases of personal identification, trauma analysis and search efforts. We argue that Sweden could benefit from making qualified forensic anthropology expertise available in all law enforcement regions, starting to implement and promote forensic anthropology in routine forensic casework and formalising the role of forensic anthropology practitioners.

Adult age-at-death estimation using the first rib: A simple probabilistic approach

Age-at-death estimation is a difficult task in fragmented or incomplete contexts. The generation and testing of methods are needed to identify their potential application in different types of osteological samples. This paper proposes a new method for age estimation using the first rib. Four hundred and fifteen individuals from the Coimbra Identified Skeletal Collections (Portugal) were studied; the sample was divided in two groups (reference and test samples), used to develop the procedure and to evaluate its reliability. The three rib joints and two variables (surface texture and topography, and periarticular margins and subsidence of the surface) were recorded. Statistical analyses were performed to test the procedure reproducibility, and side and sex variations. Posterior probabilities were calculated following Bayesian statistics and used to estimate the most likely age-at-death in the test sample. The results show the reproducibility of the method is adequate, left and right ribs can be indistinctly recorded, and both sexes show similar change patterns. The costal face and the head epiphyseal region offered satisfactory results and the percentages of correct estimations are greater for younger individuals, decreasing as ages-at-death are higher. This method is more effective among individuals in the 20-50 years cohort; nevertheless, it also offered satisfactory estimates in older ones. Overestimations in individuals younger than 40 years and underestimations in individuals older than 75 years were identified. In conclusion, the first rib offer adequate estimates when a basic probabilistic approach is chosen. Whenever possible, this proposal must be included in a multifactorial perspective with other age markers.

Sexual Dimorphism of Cranial Morphological Traits in an Italian Sample: A Population-Specific Logistic Regression Model for Predicting Sex

Simple Summary

Despite the fact that sex estimation methods from crania are very popular in forensic anthropology, few validation studies have verified their accuracy and reliability in different populations. Different from craniometrics, for which validation studies have remarkably increased lately, the methods based on cranial morphology still need to be thoroughly investigated, even if a large consensus exists on the effects of population variability on sexual cranial dimorphism. When dealing with forensic contexts, appropriately-validated methods should be applied for building accurate biological profiles. Since the possible sexual dimorphism variation of cranial morphological traits needs to be evaluated properly in various populations, in this study, we analyzed the accuracy of existing regression models for predicting sex from cranial morphological traits in an Italian contemporary/modern population. In addition, we propose new logistic regression models that are more accurate and specific for our sample. The results also update the reference standards for populations of this geographical area and provide an additional important warning on sexual dimorphism to anthropologists working in forensic contexts.

Abstract

Although not without subjectivity, the cranial trait scoring method is an easy visual method routinely used by forensic anthropologists in sex estimation. The revision presented by Walker in 2008 has introduced predictive models with good accuracies in the original populations. However, such models may lead to unsatisfactory performances when applied to populations that are different from the original. Therefore, this study aimed to test the sex predictive equations reported by Walker on a contemporary Italian population (177 individuals) in order to evaluate the reliability of the method and to identify potential sexual dimorphic differences between American and Italian individuals. In order to provide new reference data to be used by forensic experts dealing with human remains of modern/contemporary individuals from this geographical area, we designed logistic regression models specific to our population, whose accuracy was evaluated on a validation sample from the same population. In particular, we fitted logistic regression models for all possible combinations of the five cranial morphological traits (i.e., nuchal crest, mastoid process, orbital margin, glabella, and mental eminence). This approach provided a comprehensive set of population-specific equations that can be used in forensic contexts where crania might be retrieved with severe taphonomic damages, thus limiting the application of the method only to a few morphological features. The results proved once again that the effects of secular changes and biogeographic ancestry on sexual dimorphism of cranial morphological traits are remarkable, as highlighted by the low accuracy (from 56% to 78%) of the six Walker’s equations when applied to our female sample. Among our fitted models, the one including the glabella and mastoid process was the most accurate since these features are more sexually dimorphic in our population. Finally, our models proved to have high predictive performances in both training and validation samples, with accuracy percentages up to 91.7% for Italian females, which represents a significant success in minimizing the potential misclassifications in real forensic scenarios.

The repeatability of standard cranial measurements on dry bones and MSCT images

This study examined if the cranial measurements from Data Collection Procedures for Forensic Skeletal Material 2.0 are repeatable when measured in dry bones and MSCT images and if the virtual measurements correspond to the physical ones. The sample included 33 dry crania imaged by MSCT. Two observers measured dry bones, two placed landmarks on 2D and 3D MSCT reconstructions, and one conducted measurements/landmarking on both media. One of the observers for each media repeated the measurements. Technical and relative technical error of measurement (TEM and rTEM) and percentage differences were calculated to examine the repeatability of measurements and compare measuring modalities. Intraobserver rTEM was above 1.5% for six bone measurements: FOB, ZOB, OBB, NLH, DKB, MDH (1.51%-4.87%) and for seven MSCT measurements: OBH, FOB, OBB, MDH, NLB, ZOB, DKB (1.57%-5.55%). The interobserver rTEM was above the acceptable level (>2%) for 11 measurements: PAC, NLH, OBB, EKB, MAL, FOB, NLB, OBH, ZOB, DKB, and MDH (2.01%-9.34%). The percentage differences were not systematically larger for measurements taken by the same user on both modalities than those obtained by different users on the same modality. When physical and MSCT measurements were tested on sex classification standards, the proportion of crania classified as male or female did not significantly differ (p > 0.05). The study showed that physical and virtual cranial measurements could be interchangeable for developing or applying sex estimation standards. However, clarifications and adaptations are necessary for measurements of mastoid, nasal, and orbital regions that did not meet the standard criteria.

The modern Dental Cast Reference Collection from the University of Coimbra, Portugal

INTRODUCTION

Identified skeletal and skull collections are centrepiece for research in biological anthropology. However, until recently, the same relevance has not been placed on dental cast collections. This perspective evolved, mainly, with the research on population variation and human identification through dental characteristics. While dental collections exist throughout the world, their reports and documentation are scarce in the literature.

AIMS

This work aims to present the new Dental Cast Reference Collection - University of Coimbra (DCRC - UC) housed in the Laboratory of Prehistory of the Department of Life Sciences of the University of Coimbra (Portugal).

BASIC PROCEDURES

The modern dental cast collection (DCRC - UC) was created in 2016 for teaching and research purposes. The casts were obtained from volunteers who answered a brief questionnaire (sex, age, nationality, previous orthodontic and dental data) after informed consent.

MAIN FINDINGS

The collection includes the dental casts of 90 adult individuals of both sexes: 69 females and 21 males. The volunteers were students, teachers and visiting researchers of the Department of Life Sciences of the University of Coimbra. Age ranges from 17 to 49 years, including individuals of Portuguese (n=79) and non-Portuguese nationality (n=11). Lastly, the strategy of the conservation and storage conditions of the casts are underlined, a vital aspect of this working collection, emphasizing its protection while also allowing it to function as a usable resource.

PRINCIPAL CONCLUSIONS

Currently, the addition of new individuals to the dental cast collection is paused due to the COVID-19 pandemic, however the future work and expected expansion will require new logistic solutions. The DCRC - UC is an invaluable resource to both research and teaching activities.