Résumé
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.