jomifl; You quote me as saying "and anyway, insufficient is known about what actually constitutes sleep in some creatures./" and claim this to be "controversial". In saying this I'm only reflecting what you yourself said about swallows and someone else said about dolphins earlier, about sleeping on half of the brain, and is something I personally know nothing about but I give you both the benefit of the doubt.
I stick completely to my thesis that all what we consider to be animals - domestic and wild - excluding those which have no, or hardly any, brain, not only have to sleep, but all dream (and I now can include the anteater). This is obviously of paramount importance not only to humans but them too and we don't have a clue as to why it is necessary, unless that is you do.