Maxillary canine tooth growth in Babirusa (genus Babyrousa)

Abstract

Babirusa (genus Babyrousa), wild pigs from the Indonesian island of Sulawesi and neighbouring small islands, most obviously differ from other wild pigs in that the maxillary (upper) canine teeth of the males pierce through the skin of the nose and curl over the forehead. The females sometimes show small teeth piercing through the nasal skin. The process of anatomical growth of these maxillary canine teeth and the remodelling of the alveolar processes (tooth sockets) within which they grow is here illustrated and explained for the first time. Forty-four skulls in museum and private collections were studied. They represented all ages, from neonates to adult animals. The deciduous maxillary canine teeth of both sexes begin life by pointing rostrally and slightly ventrally into the oral cavity and then appear to be rotated dorsally and medially. The permanent teeth continue this process, rotating through approximately 90 degrees, from pointing rostrally to pointing dorsally through the nasal skin. The structure of the alveolar process is in the meantime modified and develops a bony flange caudally. We hypothesise that some form of connective tissue, stretching from the flange to the subcutaneous tissues of the forehead, exerts a caudally orientated pulling force that results in the gradual rotation of the alveolar process. The contributory role in this pulling force of bone growth at the facial sutures is also highlighted.