Complex sentence: The echidna was originally thought to not enter rapid eye movement sleep, but a more recent study shows they do, amounting to about 15% of the total sleep time observed for subjects at an environmental temperature of 25 ° C (77 ° F).
Split into simpler sentences: The echidna was originally thought to not enter rapid eye movement sleep. However, a more recent study showed that REM sleep accounted for about 15% of the total sleep time observed on subjects at an environmental temperature of 25 ° C (77 ° F).