Ultrastructure, biomechanical and chemical properties of the vestigial dentition of a Cuvier's beaked whale

Abstract

Beaked whales are poorly known cetaceans with a peculiar dentition consisting of one or two pairs of mandibular tusks, sometimes accompanied by dozens of peg-like rudimentary teeth normally concealed in the gum tissue. This study investigated the ultrastructure, chemical and biomechanical properties of vestigial teeth in a specimen of Cuvier's beaked whale deposited in the Otago Museum collections. The juvenile individual had 49 needle-like vestigial teeth in situ on the lower jaws. Scanning electron microscopy images revealed a thin layer of semi-structured prismless enamel covering the teeth. Mechanical properties values were within the range of values reported for other cetaceans, suggesting relaxed biomechanical functional demands. Chemical analyses revealed preservation of the hydroxyapatite composition despite morphological simplification and vestigial nature. The presumed high incidence of vestigial teeth in Ziphius cavirostris, the small size and the degenerate nature of these structures are consistent with their interpretation as vestiges rather than atavisms.