A geometric morphometric study into the ontogeny and sexual dimorphism of the human scapula

Abstract

Sex and age determination are vital when attempting to establish identity from skeletal remains. There are two methodological approaches to sex determination, namely morphological and metrical methods. In this study the shape of the scapula was studied in order to gain information on its development and sexual dimorphism. One drawback to studying the scapula is its fragility, making it difficult to obtain adequate osteometric measurements. The aim of this study was to use geometric morphometrics to study the ontogeny and sexual dimorphism of the scapula. The sample consisted of 45 adult males and 45 adult females, as well as 81 juvenile scapulae of known individuals. The scapulae were photographed and 21 homologous landmarks were plotted to use for geometric morphometric analysis with the ‘tps’ series of programs, as well as the IMP package. The consensus thin- plate splines, as well as the vector thin- plate splines for adult males and females, as well as each consecutive year of growth in juveniles were compared with each other. The CVA and TwoGroup analyses yielded significant differences between males and females. The lateral and medial borders of females are straighter and the supraspinous fossa of females was more convexly curved than those of males. More than 91% of the adult females and 95.6% of the adult males were correctly assigned. Goodall’s F- test yielded a p- value of 0.20014 which was not significant. Hotelling’s T2- test yielded a significant p- value of 0.00039. Geometric morphometrics were found to be a valuable tool in the study of changes in shape in the growing years and it was found that the lateral border of juvenile scapulae remained constant with advancing age, while the medial border remained constant during early childhood up to the age of six, varying during older childhood and early adolescence and once again becoming constant from age 15 upwards. The largest changes in the juvenile shape could be seen in the supraspinous fossa, with the superior border having a concave shape up to the age of 10, and then displaying a convex shape from 12 to 19 years of age. Differences between the sexes in juveniles were not significant, but a larger sample may yield different results. In conclusion it was found that significant differences between the shapes of adult male and female scapula exist.