Size Explosion

Whales were not always giants. Their enormous sizes appeared only in the last few million years, as ice ages packed krill and small fish into dense, cold-water swarms. A filter-feeding baleen whale could engulf such swarms in a single lunging gulp — enough food to fuel a body no land animal could match.

The blue whale, up to 100 feet long, is the largest animal known to have ever lived — bigger than any dinosaur. Water carries its weight, so its skeleton never has to. And bulk keeps it warm: a huge body loses heat slowly in freezing seas.