Skull Ontogeny and Sexual Dimorphism

The skull ontogeny and sexual dimorphism of the plains vizcacha, Lagostomus maximus, is here described from quantitative approaches. The quantitative study of allometry was performed based on 19 skull linear measurements taken from 78 specimens, using two methods: bivariate regression and multivariate allometry. Seven variables show positive allometry for both sexes in the bivariate and multivariate analyses: length of the nasals, length of the zygoma, length of the upper diastema, length of the upper cheek teeth series, height of the mandibular condyle, length of the mandible, and length of the lower cheek teeth series. Nine variables show sexual dimorphism in allometric terms: breadth of zygoma, breadth of anterior palate, breadth of posterior palate (for the bivariate analysis), height of the rostrum, length of the zygoma, length of the upper teeth series, length of the lower teeth series, length anterior to the masseteric notch, and length of the mandible (for the multivariate analysis). The results show that the braincase develops in prenatal stages, and growth of the skull after birth is mainly given by the lengthening of the rostrum, as was observed in other mammals, including caviomorph rodents. Additionally, sexual dimorphism of the skull can be related to differences in mastication.