Most REM sleep for a mammal
platypus Ornithorhynchus anatinus
8 hour(s)
Australia ()

The mammal that undergoes most REM (rapid eye-movement) sleep is the Australian platypus Ornithorhynchus anatinus, with recorded readings of more than eight hours per day, which is much greater than for any other mammal species examined. Associated with dreaming in humans, REM sleep is a type of sleep during which the brain can be more active than it is while awake, and can be recognized outwardly by the animal twitching, and its eyelids flickering. In particular, and first reported as long ago as 1860, young platypuses when asleep perform "swimming" movements with their forepaws.

The platypus is a monotreme (egg-laying mammal), and, intriguingly, the only other monotremes alive today, the echidnas or spiny anteaters, by contrast exhibit such muted REM that for a long time they were thought not to exhibit any at all. However, more recent studies confirmed that they did, but of a far less intense nature than that of the platypus. Indeed, in the echidna, REM sleep seems to be confined to the brain stem when the creature sleeps, while the forebrain remains in a state of non-REM sleep. In the platypus, as with other types of mammal, younger individuals exhibit more REM sleep than adults.