| Summary: | The evolutional pathway of communication sounds (i.e., whistles) in odontocetes is reviewed using recent acoustic and phylogenetic studies. The common ancestor of Ziphiidae, Inioidea, and Delphinoidea acquired the ability to whistle in the early Oligocene. Subsequently, Pontoporiidae, Phocoenidae, and the genus Cephalorhynchus lost the ability to whistle and evolved narrow-band high-frequency (NBHF) clicks. I hypothesize that sexual selection based on acoustic signaling contributed to the evolution of whistle. However, group size cannot be excluded as the reason for whistle emergence. The event of whistle loss and replacement with NBHF clicks occurred on three independent occasions after killer whale divergence, through the reconstruction of sound-producing organs. Species with whistle loss may use alternative methods to compensate for whistle information, such as tactile communication. Further research on acoustic communication by Ziphiidae, Inioidea, Monodontidae, and the genus Cephalorhynchus is essential to clarify the evolutional pathway of odontocete whistles. //
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