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.

Recent technological advances have allowed researchers to acquire a vast amount of information on wild cetaceans, much of which had previously been inaccessible. However, despite these new technologies, existing studies on cetaceans in captivity remain valuable. In this article, we review the recent research conducted on captive cetaceans in Japan to show their importance. We indexed the existing studies regarding behavior (resting behavior, vocal development, social behavior, and behavior differences between species), comparative cognition (echolocation ability), stress reduction,and reproductive physiology. The resulting data, as well as an understanding of the techniques used to obtain these data, will help improve the condition of cetaceans (especially endangered species) kept in captivity and fill in the gaps of studies done on cetaceans in the wild.