When most mammals go to sleep, they lie their weary heads on a pillow, the ground, or curl up in a ball. From there, they enter a state of rest, usually for several hours at a time. You know that ...

Sleeping underwater might sound peaceful — but for ocean animals, it’s a matter of survival. Some dolphins sleep with one half of their brain at a time, keeping one eye open to avoid danger and ...

If marine mammals want to sleep, they can't just close their eyes and drift away for the night, as they need to intermediately surface for air. Nor can they float at the water's surface and slumber, ...