# Sexual Dimorphism of the Lateral Angle of the Petrous Bone in Children: Growth Patterns and the Influence of Cranial Width

## TL;DR

This study shows that the lateral angle of the ear canal in skulls becomes sexually dimorphic during puberty and is linked to skull width, explaining inconsistent results in sex determination methods.

## Contribution

The study reveals that sexual dimorphism in the lateral angle appears at puberty and is associated with cranial breadth, offering a new explanation for inconsistent sex determination results.

## Key findings

- Sexual dimorphism in the lateral angle appears during puberty.
- The lateral angle is strongly associated with biauricular breadth.
- Interpopulation variability in cranial dimensions affects sexual dimorphism.

## Abstract

The lateral angle of the internal ear canal opening in the skull is sometimes used to determine the sex of human remains in biological anthropology, especially when the skeleton is damaged or burned. However, earlier studies have shown mixed results regarding the reliability of this method. This study looked at subadults to investigate if this feature is already different between boys and girls before adulthood and whether its size is related to the width of the skull. We measured the lateral angle in 204 individuals, from newborns up to 30 years old, using detailed 3D scans of 19th-century Austrian skulls. Because there were few older teenagers in this collection, additional data from modern forensic CT scans (NM, USA) were used. The results showed that the difference between males and females in the lateral angle does not appear until puberty. It was also found that the width of the skull is closely linked to the lateral angle measurements. Differences between populations were also observed. These findings help explain why earlier studies sometimes disagreed and suggest that using a single cut-off value to determine sex based on this angle may not work well for all groups of people.

Background: The lateral angle of the internal acoustic meatus of the petrous bone is a sexually dimorphic feature used for sex determination, particularly in fragmented or cremated remains. However, studies show conflicting results regarding its accuracy, and the reasons for its dimorphism remain unclear. The aim of this study is to analyze sexual dimorphism in subadult individuals and to examine the association of the lateral angle with cranial breadth as an explanation for its sexual dimorphism, as well as interpopulation differences. Methods: We measured the lateral angle and biauricular breadth in 204 individuals (birth to 30 years) using CT scans from Austrian 19th-century anatomical collections and data from the New Mexico Decedent Image Database. Results: This study revealed that the sexual dimorphism of the lateral angle and cranial dimensions manifests during puberty, along with a strong association between the lateral angle and the biauricular breadth. Additionally, this study noted interpopulation variability in cranial breadth, with different levels of sexual dimorphism observed across diverse populations. Conclusions: The findings offer a potential explanation for the observed variability in lateral angle measurements across studies and the limitations of universal cut-off points as a sex-determination method in osteology.