Whales
Mammals that returned to the sea.
Whales are marine mammals: warm-blooded, air-breathing, and they nurse their young. Their ancestors were land mammals that returned to water around 50 million years ago, and the vestigial hip bones in a modern whale are the leftover evidence.
Two suborders
| Baleen (Mysticeti) | Toothed (Odontoceti) | |
|---|---|---|
| Feeding | Filter krill and small fish through baleen plates | Hunt individual prey with teeth |
| Blowholes | Two | One |
| Size | Includes the largest animals ever | Generally smaller |
| Examples | Blue, humpback, right | Sperm, orca, dolphins, porpoises |
The blue whale reaches about 30 m and 150 tonnes, larger than any known dinosaur. Filter feeding is what makes that size possible — it is an efficient way to take enormous quantities of small prey.
Diving
Whales exhale before diving rather than filling their lungs. Oxygen is stored in blood and muscle instead, bound to haemoglobin and myoglobin at concentrations far above ours. Heart rate drops, and circulation is shunted to heart and brain. A sperm whale can stay down over an hour and reach 2,000 m.
Sound
Toothed whales echolocate, emitting clicks and reading the returning echoes to build a picture of their surroundings — enough resolution to distinguish prey species in total darkness. Baleen whales instead produce very low-frequency song that carries hundreds of kilometres; humpback song is structured, repeated, and changes across a population over a season.