Ann H. Ross

Sexual dimorphism in America: geometric morphometric analysis of the craniofacial region.

Abstract:  One of the four pillars of the anthropological protocol is the estimation of sex. The protocol generally consists of linear metric analysis or visually assessing individual skeletal traits on the skull and pelvis based on an ordinal scale of 1–5, ranging from very masculine to very feminine. The morphologic traits are then some how averaged by the investigator to estimate sex. Some skulls may be misclassified because of apparent morphologic features that appear more or less robust due to size differences among individuals. The question of misclassification may be further exemplified in light of comparisons across populations that may differ not only in cranial robusticity but also in stature and general physique. The purpose of this study is to further examine the effect of size and sex on craniofacial shape among American populations to better understand the allometric foundation of skeletal traits currently used for sex estimation. Three‐dimensional coordinates of 16 standard craniofacial landmarks were collected using a Microscribe‐3DX digitizer. Data were collected for 118 American White and Black males and females from the W.M. Bass Donated Collection and the Forensic Data Bank. The MANCOVA procedure tested shape differences as a function of sex and size. Sex had a significant influence on shape for both American Whites (F = 2.90; d.f. = 19, 39; p > F = 0.0024) and Blacks (F = 2.81; d.f. = 19, 37; p > F = 0.0035), whereas size did not have a significant influence on shape in either Whites (F = 1.69; d.f. = 19, 39; p > F = 0.08) or Blacks (F = 1.09; d.f. = 19, 37; p > F = 0.40). Therefore, for each sex, individuals of various sizes were statistically the same shape. In other words, while significant differences were present between the size of males and females (males on average were larger), there was no size effect beyond that accounted for by sex differences in size. Moreover, the consistency between American groups is interesting as it suggests that population differences in sexual dimorphism may result more from human variation in size than allometric variation in craniofacial morphology.

Sex Determination from Hand and Foot Bone Lengths

ABSTRACT: Numerous studies have addressed sex estimation from the hands and feet with varying results. These studies have utilized multiple measurements to determine sex from the hands and feet, including measures of robusticity (e.g., base width and midshaft diameter). However, robusticity measurements are affected by activity, which can disguise underlying patterns of sexual dimorphism. The purpose of this study is to investigate the utility of length measurements of the hands and feet to estimate sex. The sample consists of white females (n=123) and males (n=136) from the Terry Collection. Discriminant function analysis was used to classify individuals by sex. The left hand outperformed both the right hand and foot producing correct classification rates exceeding 80%. Surprisingly, the phalanges were better sex discriminators than either the metacarpals or metatarsals. This study suggests that length measures are more appropriate than robusticity measures for sex estimation.

Cranial Thickness in American Females and Males

To date, numerous studies have examined the range of cranial thickness variation in modern humans. The purpose of this investigation is to present a new method that would be easier to replicate, and to examine sex and age variation in cranial thickness in a white sample. The method consists of excising four cranial segments from the frontal and parietal regions. The sample consists of 165 specimens collected at autopsy and 15 calvarial specimens. An increase in cranial thickness with age was observed. The results suggest that cranial thickness is not sexually dimorphic outside the onset of hyperostosis frontalis interna (HFI).

Testing Repeatability and Error of Coordinate Landmark Data Acquired from Crania

Abstract:  This study evaluates issues of precision, repeatability, and validation in three‐dimensional (3D) landmark coordinates. Two observers collected 19 homologous cranial landmarks from three skulls during three separate digitizing sessions. Statistical analysis was conducted on the 171 interlandmark distances (ILDs) derived from the original coordinate data. A mixed model ANOVA detected significant within‐subject error in 54 of the 171 ILDs (i.e., 32%). A GLM procedure revealed significant between‐observer variation in 14 ILDs and significant observer‐by‐session differences in 13 ILDs. The majority of these differences involved ILDs with type 3 landmarks as endpoints, such as euryon and alare. Unlike type 1 and 2 landmarks which are biologically informative in all directions, type 3 landmarks contain a substantial arbitrary component. Thus, it is not surprising type 3 landmarks displayed significant digitizing error. Given these results, we caution researchers to be mindful of type 3 landmarks measurement discrepancies when selecting landmarks for coordinate data evaluation.

Allocation of crania to groups via the "new morphometry".

An investigation regarding the variation in cranial morphology between American blacks and whites was conducted using triangulation schemes of inter-landmark distances and converting these to three dimensional coordinate data. A least squares superimposition method and Euclidean distance analysis were utilized to obtain parameters for classifying individuals in our sample, consisting of 19 black and nineteen white crania from the William M. Bass, III Donated and Forensic collections curated at the University of Tennessee, Knoxville. Thirty-six caliper measurements were collected on each skull based on 14 homologous cranial landmarks (nasion, bregma, lambda, prosthion, subspinale, basion, frontomalare (left and right), zygoorbitale (left and right), zygotemporale (left and right), and left and right asterion). The results are compared to traditional discriminant analysis. The classification results using the new morphometry are comparable to traditional discriminant analysis. However, the new morphometry can provide information as to the specific location of morphological variation that cannot be obtained with discriminant analysis.

Implications of dimorphism, population variation, and secular change in estimating population affinity in the Iberian Peninsula.

Morphometric cranial variation among Spanish samples was compared to a 19th century Portuguese sample using both traditional and three-dimensional approaches. The Spanish samples included the regional 19th century Oloriz collection and the local 16-17th century Villanubla and Vallolid sample from northwestern Spain. Results suggest moderate variation among the samples and suggest that varying patterns of regional variation, sexual dimorphism and secular change represent important factors to be considered in the evaluation of population affinity using craniometric approaches.

A geometric morphometric approach to sex determination of the human adult os coxa.

Abstract:  Sex determination of the human skeleton is best assessed from the os coxa. The present study explored the possibility of using three‐dimensional landmark coordinate data collected from various landmarks located over the entire bone to determine whether there were significant sex differences local to the landmarks. Thirty‐six landmarks were digitized on 200 African American and European American male and female adult human os coxae. MANCOVA results show that sex and size have a significant effect on shape for both European Americans (Sex, F = 17.50, d.f. = 36, 63, p > F = 0.0001; Size, F = 2.56, d.f. = 36, 63, p > F = 0.0022) and African Americans (Sex, F = 21.18, d.f. = 36, 63, p > F = 0.0001; Size, F = 2.59, d.f. = 36, 63, p > F = 0.0005). The discriminant analysis shows that sexing accuracy for European Americans is 98% for both males and females, 98% for African American females, and 100% for African American males.

Craniometric Variation in the Americas

AbstractCraniofacial variation is investigated in Latin America and the Caribbean. The samples included in this study are two historic and one prehistoric sample from Ecuador; prehistoric and modern Cuban samples; a prehistoric Peruvian sample; two prehistoric Mexican samples and one contemporary admixed Mexican sample; a 16th/17th-century Spanish sample; and Terry blacks. Biological distance is investigated using traditional craniometrics by computing size and shape variables according to Mosimann and colleagues. This study shows that there is much biological variation within the Americas.

Estimation and Evidence in Forensic Anthropology

Identifications in forensic anthropology occur in two rather different contexts. One context is that of “estimation,” when a biological profile from unidentified remains is built in the hope of eventually identifying said remains. Another context is in evidentiary proceedings, where biological information from the remains is used to contribute to a probability statement about the likelihood of a correct identification. Both of these contexts can occur when stature is the biological parameter of interest, and so the authors take data related to stature as the example in this chapter. The unifying method in both contexts is the application of Bayes’ theorem. Therefore, this chapter opens with a review of some of the characteristics of a Bayesian analysis.

New identification criteria for the Chilean population: Estimation of sex and stature.

In the analysis of human skeletal or otherwise unidentifiable remains the assessment of sex is an initial vital element when rendering a biological profile. As such other aspects of the biological profile are sex-specific (e.g. stature and age) and cannot be successfully determined without this preliminary assessment. In addition, the estimation of stature is an essential parameter of the biological profile, which is often used to confirm or exclude presumptive identifications. The purpose of this study is to present newly developed local identification criteria for the estimation of sex from the postcrania and stature for Chileans. Linear discriminant functions were derived for the humerus and femur. Sexing accuracies of 87%, 86%, and 82% were achieved. Furthermore, new univariate predictive stature equations are presented using a Bayesian approach for the humerus, femur and tibia.