the platypus

The platypus, apparently, is a surprisingly deep sleeper. What's more, it spends more of its time in so-called 'REM' sleep than any other mammal. These are the conclusions of a study on sleep in the platypus by Jerry M. Siegel of the Sepulveda Veterans' Affairs Medical Center, North Hills, California and colleagues. Their report appears in a special number of Philosophical Transactions of the Royal Society devoted to the biology of the platypus (Ornithorhynchus anatinus), …

…sleep on a firmer footing. It now seems that the 'core' brainstem activity manifested as REM sleep has extremely ancient roots, going back to the reptilian acnestors of mammals as well as birds. The elaboration of REM sleep into the forebrain is a later innovation: but whether it evolved once and monotremes have since lost it, or if it evolved more than once, is something that only more work on birds and reptiles can establish.