Assessment of Sexual Dimorphism on the First and Second Ribs: Exploring Geometric Morphometrics

Estimating the sex of unknown human skeletal remains is important to the fields
of forensic anthropology, bioarchaeology, and other specialties. I studied sexual
dimorphism on the first and second ribs to estimate sex from skeletal remains. I
employed two approaches. I used geometric morphometrics to analyze landmark and
semilandmark coordinate points to examine the overall shape of the ribs. I also examined
the sternal end of the ribs for size using the superior-inferior height (SIH) and anteriorposterior
breadth (APB) in a binary logistic regression (BLR) model. Differences in male
and female first and second ribs are undetectable when landmark coordinate points are
used to capture shape variability, but significant differences in the shape of the ribs,
however, are detected through the use of semilandmark coordinate points.
Using semilandmark points to estimate sex presented an accuracy rate of 80.7%
from the first rib, and 72.9% from the second rib. The use of the sternal end presents
consistent results in its ability to estimate sex with an accuracy rate of 84.2%. The BLR model reveals significant differences between males and females than the geometric
morphometric approach; it is more applicable for discerning sexual dimorphism of
unknown individuals. This study reveals that while geometric morphometrics provides a
powerful approach to assessing morphological differences, it is not always better than
simpler methods, in this case, simple measurements analyzed through BLR.