The purpose of circadian rhythms is to be able to dapt to changes, though we don't quite know if one small disruption of circated rhythms has lasting effects on the body. Giant armadillos apparently sleep 18 hours a day; cowalas and little brown bats have been observed snoozing for almost 20 hours a day. But they were curious about sloths, so they fitted wild ones with little fitbits or something, and they showed they only sleep nine and a half hours a night.