Structural and mechanical characteristics of the hyperdense bone of the rostrum of Mesoplodon densirostris (Cetacea, Ziphiidae): Summary of recent observations

Abstract

This note provides a brief account of several recent studies of the basic physical properties, histology and ultrastructure, and biomechanical behaviour of the bone that forms the rostrum of the beaked whale Mesoplodon densirostris. The density (2.612 to 2.686 g cm⁻³), mineral content (86% to 87%) and compactness (99%) of this bone reach the highest values hitherto observed for mammalian bone. Histologically, the rostrum is composed of dense Haversian tissue, the secondary osteons of which are oriented longitudinally, themselves consisting of hypermineralized parallel‐fibered osseous tissue. The ultrastructure of the walls of the secondary osteons is characterized by a strong volumetric reduction of the collagenous network, which is composed of very thin fibrils (0.017 μm in diameter) that are oriented longitudinally. The biomechanical behaviour of the rostrum is that of an exceptionally rigid (Young's modulus up to 46.9 GPa), hard (hardness > 200 VHN) but also very brittle (bending strength > 59 MPa) material. These data are discussed in reference to the possible functional role(s) of the hyperdense rostrum.

Keywords:

• Whale
• Rostrum
• Bone
• Density
• Mineralization
• Histology
• Ultrastructure
• Biomechanics
• Mesoplodon densirostris

Notes

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