Postweaning ontogeny of the skull of Didelphis albiventris

Postweaning development of the skull of Didelphis albiventris was studied i n juveniles (3.5-8 months), subadults (7.5-9.5 months), and adults (>9.5 mo nths). Analysis of allometry of 15 skull measurements was performed on a co ntinuous growth series of 52-61 specimens to evaluate quantitative ontogene tic changes. Complex modifications occurred in cranial bones or regions suc h as the palate, processes for origin and attachment of jaw muscles, mandib ular joint, frontal region, braincase, occipital bones, and petrosal.. All measurements except zygomatic breadth were either positively or negatively allometric. Neurocranial components grew with strongly negative (<1) coeffi cients of allometry. Adult proportions of the masticatory apparatus arose f rom the counteraction of developmental trends; for example, the space for l arge temporal muscles was provided by isometric growth of the zygomatic bre adth versus slower growth of the braincase. We interpret most of the postwe aning developments as a function of the shift from milk suckling to active mastication.