How whales and dolphins evolved for life at sea
Less genes for a life in water
Orcas Hunting Seal Video in Antarctica Reveals Dolphin Intelligence
How Do Whales Sleep? All Your Questions, Answered
Where Do Whales Sleep?, Dana Point
How do dolphins sleep and breathe? - Azores Whales
How Do Whales and Dolphins Sleep? - Waggoner
An extinct giant dolphin was more like a killer whale, study finds
This is how whales look like when they sleep along side one
Elephant seals drift off to sleep while diving far below the ocean
Whales sleep with half their brain to avoid drowning