Whales split into two kinds
The archaeocetes give rise to the toothed whales and the baleen whales, and the two never converge again.
- When
- —
- Duration
- 3.9 million years
- Known to
- ± 2 million years
- Era
- Oligocene, Cenozoic
Near the Eocene-Oligocene boundary the surviving whales divide into Odontoceti, which keep teeth and develop echolocation, and Mysticeti, which will eventually replace teeth with baleen and filter-feed. The division follows the reorganisation of the Southern Ocean: stronger circulation and upwelling create dense, patchy concentrations of small prey that reward bulk filtering, while high-frequency hearing opens a way to hunt in dark or turbid water. Both strategies are still in use.