Sexual Dimorphism and Morphological Disparity in the Shapes and Sizes of the Cranium, Scapula, Mandible and Pelvis of Selected Murid Rodents

The sex of a captured rodent is usually determined based on external features only such as the presence of testes and teats in mature males and females, respectively, posing impediments in the identification of the sex of specimens based on some skeletal elements. Recent advances in geometric morphometrics (GM) and multivariate analyses can help remedy the discrepancy. Thus, this study was conducted to observe, describe and compare the differences in the shapes and sizes of the cranium, scapula, pelvis, mandible and between sexes among the four species of murid rodents, namely: Mus musculus Linnaeus, Rattus argentiventer Robinson and Kloss, R. norvigicus Berkenhaut, and R. rattus mindanensis Mearns. Results show that the magnitude of sexual dimorphism with regards to the shape of the skeletal elements differs among species - the largest between the sexes of R. r. mindanensis. However, subtle differences in sizes can be seen among the species. Shape disparity between the females of R. r. mindanensis and R. argentiventer is large and is observed to be a function of differences in the shape of the cranium as seen from the lateral and dorsal orientations, pelvis, and scapula. However, differences can also be observed between the males of these species with regards to the shapes of the scapula with only subtle disparity in the shapes of the mandible. The females of these species differ in the size of the cranium when measured in both dorsal and ventral orientations. The results of the study underscore the need to incorporate GM methods in rodent taxonomy and in the identification of specific features rendering sexual dimorphism in murid rodents