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The voice boxes of baleen whales evolved a unique set of structures to communicate sound underwater, according to a study published yesterday. The discovery solves a 50-year-old mystery that has puzzled researchers since the first baleen whale songs were recorded in 1967 (read the story).
All whales evolved from ancestral land mammals with voice boxes, or larynxes, roughly 50 million years ago (see explainer). Unlike their cousins, the toothed whales (orca, sperm), baleen whales—defined by their bristly plates of keratin used for filter-feeding—did not evolve nasal structures to emit sound. By piping air through three surgically removed larynxes from beached baleen whales, researchers observed a set of vocal folds vibrating against a fatty tissue to produce sound in an unparalleled way.
Using digital models, the analysts also determined baleen whales can only produce sounds at a low frequency at relatively shallow depths, suggesting shipping noises may disrupt their communication. Listen to humpback whale sounds here.