Allometric shape variation in Ovis aries mandibles: a digital morphometric analysis.

Abstract

Morphological differences among 75 specimens of domestic sheep were investigated using landmark-based geometric morphometrics of the lateral aspect of the left hemimandible. The set was grouped at different ages according to tooth eruption: first molar (M) erupting (n=28), only first molar erupted (n=18), only second molar erupted (n=4), and all three molars erupted (n=25). The link between centroid size and shape was significant. This showed that the differences in mandible shape were due to allometry, which can be explained by changes in elongating molar length (expanding rostro-nuchally with age) and the corresponding pars molaris of the corpus mandibulae (margo ventralis). These changes could be also related to a certain morphofunctional change, as they correspond to insertion points of important masticatory muscles: mylohyoideus, digastricus, masseter and pterygoideus medialis.