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Cetaceans use sound for communication, navigation and finding prey. Most extant odontocetes produce broadband (BB) biosonar clicks covering frequency ranges from tens of kilohertz to 150–170 kHz. In contrast, the biosonar clicks of some odontocetes are unique, being narrow in bandwidth with high centroid frequency (NBHF), peak frequencies being at 125–140 kHz and bandwidths of 11–20 kHz. Thirteen species within four families (Phocoenidae, Pontoporiidae, Kogiidae, Delphinidae) are known to produce these signals, implying convergent evolution under strong selective drivers. Several hypotheses have been proposed, including acoustic crypsis to escape predation by killer whales, but none has provided comprehensive explanation of the timing of NBHF evolution and the pressures driving sound production to such extremes. Using molecular phylogenetics and the cochlea anatomy of extinct and …