Sexual dimorphism in skeletal browridge and chin morphologies determined using a new quantitative method

Abstract

Qualitative methods of describing sexual dimorphism in discrete cranial traits have been criticized for their subjectivity and statistical limitations. However, researchers have yet to be able to accurately capture the morphology of these individual traits using traditional metric techniques. This article presents a method to quantify morphological variation in the skeletal browridge and chin using 3D surface laser scans. Browridge and chin regions are isolated from the skull using objectively defined landmarks and planes. Region areas and volumes are used to quantify absolute and relative size, while semilandmarks along transects are used for more detailed morphometric analyses. An intraobserver error study indicates high repeatability of the method. Application of the method is demonstrated on a sample of US males and females of black and white ancestries. Results suggest significant effects of both sex and ancestry on brow and chin morphologies and are consistent with traditional qualitative descriptions. Our results indicate that the method can accurately and reliably quantify browridge and chin morphologies, providing a tool to objectively describe and statistically analyze these traditionally qualitative discrete cranial traits.

Geographic Variation in Chin Shape Challenges the Universal Facial Attractiveness Hypothesis

“…Thus, geographic variation in chin shape appears to be a general feature of recent human evolution. This observation, when combined with previous evidence of sexual dimorphism in chin shape [32], [33], suggests the possibility of region-specific chin shape preferences in some parts of the world.…”

“…The hypothesis that chin shape has undergone sexual selection in humans is supported by recent evidence that males and females differ with regard to chin shape [33]. In a previous study [34], we developed a morphometric technique for quantifying chin shape using elliptical Fourier functions analysis, or EFFA [35].…”

Three-dimensional laser scanning: potential uses for museum conservation and scientific research

“…After all the pins were placed on the specimen, the variables were exported (as x, y, z coordinates for each recorded landmark) into software that is used to explore similarities and differences in the craniofacial shape of prehistoric Californians. Beyond cranial landmarks, the digital models are also useful for studies that focus on regions of the skull, like the face, jaw, cranial vault, or base (see Garvin and Ruff, 2012 for a recent study).…”

“…Furthermore, published manuscripts that discuss and utilize 3D laser scanners in the study are typically aimed at specialists in the field of paleoanthropology, medicine, biology, and forensic science; the studies tend to focus more on sophisticated methods that are used to analyze 3D scans, such as finite element analysis, geometric morphometrics, and elliptical Fourier techniques (e.g. Friess, 2010;Garvin and Ruff, 2012;Hennessey et al, 2002;Relvas et al, 2011;Sholts et al, 2011). These technical papers can be difficult for the novice user to follow.…”

Topographic analysis of the mandibular symphysis in a normal occlusion population using cone-beam computed tomography

“…some gender differences were noted between male and female subjects. In previous studies, the interforaminal distance, anterior loop, horizontal distance, cortical bone thickness, and vertical distance values were increased in male subjects, as compared with female subjects (27)(28)(29). Thus suggesting that increased care should be taken to determine what block-bone depth is required in female patients.…”