Sea lions are marine mammals and members of the otariidae family. They share their existence between land and sea. Even if they can't breathe underwater they are perfectly adapted for swimming and therefore hunting at sea. They go on land only to rest. They sleep about 12 hours a day. In the water, they can also rest but by practicing unilateral sleep: only one hemisphere of their brain at a time is asleep while the other one remains awake. Thus, they sleep with one eye open and remain alert to dangers. Photo credit: Chris Stenger