Physeteridae

About the sperm whales

The family is now monotypic, though it was diverse through the Miocene. Its defining structure is the head, which in a mature male is up to a third of total body length and is almost entirely a sound-production organ: the spermaceti organ and the junk, two masses of waxy oil separated by the right nasal passage, with the phonic lips at the front. Clicks generated there and focused through the junk have been measured above 230 decibels, the loudest sound produced by any animal.

Functional teeth are confined to the narrow lower jaw, where they fit into sockets in the upper. They appear to matter less for feeding than the name suggests — animals with badly deformed jaws are found in good condition — and suction is thought to do most of the work. Prey is cephalopod, taken on dives that routinely pass a thousand metres and last around an hour.

Sexual dimorphism is extreme even for a toothed whale: males reach sixteen to eighteen metres and roughly three times the mass of a female. Females and young live in stable matrilineal units in tropical and warm temperate water; males leave in adolescence for high latitudes and return only to breed. Units belong to vocal clans with distinct repertoires of coda click patterns, learned rather than inherited, and clans that share an ocean do not mix.