Data from: Early evolution of the ossicular chain in Cetacea: into the middle ear gears of a semi-aquatic protocetid whale

Modifications of the morphology and acoustic properties of the ossicular chain are among the major changes that accompanied the adaptation of Cetacea to the aquatic environment. Thus, data on the middle ear ossicles of early whales are crucial clues to understand the first steps of the emblematic terrestrial/aquatic transition that occurred in that group. Yet, the delicate nature and very small size of these bones make their preservation in the fossil record extremely rare. Due to the scarcity of available data, major questions remain concerning the sound transmission pathways in early non-fully aquatic whales. Virtual reconstruction of a partially complete ossicular chain of an Eocene protocetid whale documents for the first time the three ossicles of a semi-aquatic archaeocete. Contrary to previous hypotheses, these ossicles present different evolutionary patterns, showing that the ossicular chain does not act as a single morphological module. Functional analyses of the different middle ear units highlight a mosaic pattern of terrestrial and aquatic signatures. This integrative anatomical and functional study brings strong evidence that protocetids were adapted to their dual acoustic environment with efficient hearing in both air and water.

鲸类（Cetacea）适应水生环境的过程中所伴随的诸多重大演化改变之一，便包括听小骨链（ossicular chain）的形态与声学特性改造。因此，早期鲸类中耳听小骨的相关研究数据，是解析该类群标志性陆生向水生过渡初始阶段的关键线索。但这类骨骼质地脆弱且体型微小，使其在化石记录中极难保存，相关数据极为稀缺。受限于现有数据的匮乏，学界关于非完全水生早期鲸类的声音传导通路仍存在诸多核心未解问题。本研究对一件始新世原鲸类（protocetid）鲸鱼的部分完整听小骨链开展虚拟重建，首次报道了半水生古鲸类（archaeocete）的三块听小骨。与此前的学术假说相悖，这些听小骨呈现出各异的演化模式，表明听小骨链并非作为单一形态模块行使功能。对不同中耳单元的功能分析，揭示出其兼具陆生与水生特征的镶嵌演化格局。这项整合了解剖学与功能学研究方法的工作，提供了有力证据：原鲸类已适应其双重声学环境，可在空气与水体中均实现高效听觉。