the.com/cetaceans
Mammals that quit land, kept their lungs, and got cosmically better at swimming.
means The aquatic mammal group containing whales, dolphins, and porpoises, all breathing air through blowholes.
from From Greek ketos, sea monster, via Latin cetus — the same root behind the biblical leviathan and the constellation Cetus.
Ex-walkersEvolved from hoofed land mammals 50 million years ago.
Closest cousinThe hippopotamus, oddly enough.
Half-asleepBrains rest one hemisphere at a time to keep breathing.
Nose movedNostrils migrated to the top as blowholes.