Possible functions of the rostrum of Blainville’s beaked whale (Mesoplodon densirostris)

The rostrum of Blainville's beaked whale, Mesoplodon densirostris, becomes secondarily ossified, particularly in males, as individuals mature. This mesorostral ossification forms the densest bone currently known and represents a considerable investment of resources for this species. Three functions for this mesorostral ossification have been proposed: prevention of damage to the rostrum during aggressive male-male interactions, ballast to aid deep diving, and sound transmission. These functions were assessed using data from museum specimens and observations of this species in the wild. Prevention of damage to the rostrum during aggressive male-male interactions was found to be the most likely function, based on the currently available data.