Bottlenose Dolphins: Dolphins sleep with only half of their brain at a time, while the other half remains awake
Bullfrogs: These amphibians can go for months without fully sleeping. They enter a state of rest where they are still alert and can react to threats
Giraffes: Giraffes sleep for short periods (usually less than 5 minutes at a time) and often standing up. They achieve REM sleep (rapid eye movement) while standing
Elephants: These large mammals sleep for around 2-4 hours a day, often in short, intermittent bouts. They also sleep standing up or leaning against a tree
Sharks: Many shark species need to keep moving to pass water over their gills for oxygenation, so they cannot afford to fully sleep like humans
Horses: Horses sleep standing up using a special mechanism in their legs called the "stay apparatus" that allows them to lock their knees and hips
Walruses: These marine mammals can sleep underwater, sometimes floating near the surface with their tusks hooked onto ice or rocks
Cows: Cows sleep for short periods throughout the day, totaling about 4 hours. They have the ability to sleep standing up or lying down