The rostrum of the toothed whale Mesoplodon densirostris is notable for the density of its bone. We examined the mechanical, fractographic, and chemical properties of the rostral material for two purposes: 1) to determine the properties of bone of an extreme density, and to compare these properties with other similar, and also more ordinary, bone; 2) to determine whether the mechanical properties could give any clues as to the function of the very dense rostral bone.
The bone was found to be the most highly mineralized, stiffest, and hardest bone known. It was very weak in bending. The salient properties of the bone, and those of two others which are given for comparison are:
The specific mechanical properties as such are very poor and it is difficult to envisage a particular mechanical function for the rostrum. Being weak, it is unlikely that it would be useful in intra- or interspecific fighting. It is possible that the high density has a significance in the emission of sonar signals.