Ontogenetic morphology and allometry of the cranium in the common European mole (Talpa europaea)

The common European mole (Talpa europaea) has been the focus of many studies because of its fossorial lifestyle and related sensory and postcranial specializations. However, because of extensive fusion and pneumatization of the adult skull, many aspects of the cranial morphology of T. europaea are poorly understood. Here we present the 1st detailed study of cranial development in T. europaea, using an ontogenetic series of cleared and stained prenatal specimens to examine bone homologies, sequence of ossification, and prenatal allometry. The enigmatic lacrimal, jugal, and mastoid bones are all identified in prenatal specimens. The jugal and lacrimal bones fuse with the maxilla during prenatal growth, explaining previous difficulties with their identification in adults. T. europaea is anomalous among placental mammals in delaying the ossification of the alisphenoid and the orbitosphenoid until after birth. Analyses of allometry for 16 measures of individual bones show marked differences when postnatal specimens are included or excluded. Coefficients of allometry based on prenatal specimens are nearly twice those of analyses including subadult specimens. Comparisons with other taxa are limited by the lack of similar prenatal data, but the pattern exhibited by T. europaea differs significantly from those observed in studies of postnatal allometry in other mammals. These results may reflect differences among taxa or between prenatal and postnatal stages.