It long seemed as if African elephants were the champions of the all-nighter. They can get by on about two hours of sleep. Other mammals need much more, like koalas (20 hours) or you (at least seven plus at least one strong cup of coffee).
But the largest living mammals on land have some competition at sea. Northern elephant seals are also able to sustain themselves on about two hours' sleep, according to a study published recently in the journal Science.
