1 Department of Osteology and Biomechanics, University Medical Center Hamburg-Eppendorf , Lottestrasse 59, 22529 Hamburg , Germany.
2 Institute for Terrestrial and Aquatic Wildlife Research, University of Veterinary Medicine Hannover , Foundation, Werftstrasse 6, 25761 Buesum , Germany.
Proc Biol Sci. 2018 Dec 19;285(1893):20181820. doi: 10.1098/rspb.2018.1820.
The auditory ossicles-malleus, incus and stapes-are the smallest bones in mammalian bodies and enable stable sound transmission to the inner ear. Sperm whales are one of the deepest diving aquatic mammals that produce and perceive sounds with extreme loudness greater than 180 dB and frequencies higher than 30 kHz. Therefore, it is of major interest to decipher the microstructural basis for these unparalleled hearing abilities. Using a suite of high-resolution imaging techniques, we reveal that auditory ossicles of sperm whales are highly functional, featuring an ultra-high matrix mineralization that is higher than their teeth. On a micro-morphological and cellular level, this was associated with osteonal structures and osteocyte lacunar occlusions through calcified nanospherites (i.e. micropetrosis), while the bones were characterized by a higher hardness compared to a vertebral bone of the same animals as well as to human auditory ossicles. We propose that the ultra-high mineralization facilitates the unique hearing ability of sperm whales. High matrix mineralization represents an evolutionary conserved or convergent adaptation to middle ear sound transmission.
听觉小骨——锤骨、砧骨和镫骨——是哺乳动物身体中最小的骨头，能够将稳定的声音传递到内耳。抹香鲸是潜水最深的水生哺乳动物之一，它们能够发出和感知超过 180 分贝、频率高于 30 千赫兹的极端响亮的声音。因此，破解这些无与伦比的听力能力的微观结构基础是非常重要的。我们使用一系列高分辨率成像技术，揭示了抹香鲸的听觉小骨具有高度的功能性，其基质矿化程度极高，超过了它们的牙齿。在微观形态和细胞水平上，这与骨单位结构和通过钙化纳米球（即微孔骨化）形成的骨细胞腔隙闭塞有关，而与同一动物的脊椎骨以及与人类听觉小骨相比，这些骨骼的硬度更高。我们提出，超高的矿化度有助于抹香鲸独特的听力能力。高基质矿化是一种对中耳传音的进化保守或趋同适应。
