Odontoceti

About the toothed whales

Odontocetes kept their teeth and added a sense. Air driven past phonic lips in the nasal passages produces clicks, which are focused forward through the melon — a lens of acoustically graded fat — and whose echoes are received through fat bodies in the lower jaw and conducted to the ear. Building that apparatus has left the odontocete skull conspicuously asymmetric, the only such asymmetry in mammalian skulls, and reduced the paired blowholes of their ancestors to a single opening.

The toothed whales in this atlas are its deep-water specialists: the sperm whales, the beaked whales, and the two Arctic members of Monodontidae. Between them they hold the mammalian records for both depth and duration of a breath-hold dive. Sustaining those dives means very high myoglobin concentrations in the muscle, collapsible lungs, and a circulation that can shut down everything but the heart and brain.

Sexual dimorphism runs the opposite way to the baleen whales: males are the larger sex, sometimes dramatically so, and in the beaked whales carry tusks used against each other. Social organisation is correspondingly more elaborate, with stable matrilineal groups and vocal repertoires that differ between populations in ways that are learned rather than inherited.