Elastic Modulus of Cetacean Auditory Ossicles

Abstract

In order to model the hearing capabilities of marine mammals (cetaceans), it is necessary to understand the mechanical properties, such as elastic modulus, of the middle ear bones in these species. Biologically realistic models can be used to investigate the biomechanics of hearing in cetaceans, much of which is currently unknown. In the present study, the elastic moduli of the auditory ossicles (malleus, incus, and stapes) of eight species of cetacean, two baleen whales (mysticete) and six toothed whales (odontocete), were measured using nanoindentation. The two groups of mysticete ossicles overall had lower average elastic moduli (35.2 ± 13.3 GPa and 31.6 ± 6.5 GPa) than the groups of odontocete ossicles (53.3 ± 7.2 GPa to 62.3 ± 4.7 GPa). Interior bone generally had a higher modulus than cortical bone by up to 36%. The effects of freezing and formalin-fixation on elastic modulus were also investigated, although samples were few and no clear trend could be discerned. The high elastic modulus of the ossicles and the differences in the elastic moduli between mysticetes and odontocetes are likely specializations in the bone for underwater hearing.

Enigmatic ear stones: what we know about the functional role and evolution of fish otoliths

“…In cetaceans, modelling of sound stimulation of the ears through different anatomical structures of the skull bone, the bony ears and soft tissue (e.g. Tubelli et al, ; Cranford & Krysl, ) has yielded exciting new insights into ear functioning. Outcomes of (or predictions derived from) mathematical modelling, however, may be debated [compare, for example, Lychakov & Rebane, and Krysl et al, ].…”

Ultra-high matrix mineralization of sperm whale auditory ossicles facilitates high sound pressure and high-frequency underwater hearing

“…The sound is then transmitted to the auditory ossicles; malleus, incus and stapes that have been found to be of dense compact bone [3,6]. A high mineralization of bone was found to be of major importance for sound perception as supported by an 86% mineralization of the tympanic bulla with an impressively high Young's modulus [7,8] resulting from mineralization and causing high impedance (a rough approximation of the impedance in case of a wave hitting a material in orthogonal direction can be written by the following equation: Z ¼ ffiffiffiffiffiffiffiffiffi r Á E p ; where Z ¼ impedance, r ¼ density of a material and E ¼ Young's modulus of a material referring to [7]).…”

Resonance of the tympanoperiotic complex of fin whales with implications for their low frequency hearing

“…As the true Young’s modulus of the bone is uncertain, the range of values that we considered reasonable for the model inputs led to a wider range of possible frequencies and possible modes. The elastic moduli measured by Tubelli et al 2004 [ 10 ] for fin whale ossicles are broad, and may be considered an upper bound, given that bone is porous, and the nanoindentation method they used was by definition applied to the solid framework of the bone. Additionally, the skull used in the experiment had been dried for some time, and studies have shown that Young’s modulus may increase for dried bone [ 14 ].…”

“…Citation: Morris M, Krysl P, Hildebrand J, Cranford T (2023) Resonance of the tympanoperiotic complex of fin whales with implications for their low frequency hearing. PLoS ONE 18 (10): e0288119. https://doi.org/10.1371/journal.…”