Stranding of a Hector's Beaked Whale ( <scp> <i>Mesoplodon hectori</i> </scp> ) (Gray 1871) From South Australia Unearths Novel Additional Teeth

ABSTRACT Most extant beaked whales have reduced dentition of one or two pairs of tusk‐like, mandibular teeth that erupt through the gum only in adult males. Additional teeth have been recorded in several species and genera. A juvenile Hector's beaked whale (SAMA M26434) having additional teeth was collected in South Australia and its skeleton and tissues examined. Ultrastructural and chemical data of one additional tooth were obtained using Energy‐Dispersive X‐ray, Scanning Electron Microscopy and nanoindentation. Skull and skeleton features were consistent with this species: slender mandible, laterally‐compressed, triangular main teeth at its tip; short rostrum; narrow vertex; wide, straight‐sided gap between premaxillary crests. Analysis of mtDNA and nuclear genes placed M26434 in a clade with conspecifics. A small, additional tooth was found dorsal to each main tooth. It had moderately thick, prismless enamel and a well‐defined enamel–dentine junction. Ca and P were the main components of enamel and dentine. Concentrations of P 2 O 5 and MgO were higher in dentine while concentrations of CaO and Na 2 O were higher in enamel. Mechanical properties of hardness and elastic modulus revealed lower values in dentine than enamel. Simplified microstructure and lower mechanical properties of the enamel point to the additional teeth being vestigial/rudimentary. Beaked whales may hold important clues to the evolutionary significance of additional teeth.