There is hardly a corner of this planet without perfectly-adapted life evolving into it. So how about above the clouds?
Back in the 50s & 60s there were reports of falls of a mysterious substance called Angel Hair, a phenomenon not recently reported. I've often wondered if diaphonous gas-bag creatures used to fill our skies, solar heated and so vast and light that the tiniest temperature difference would keep them afloat. And the era of jetliners ploughed through them and wiped them out before we knew they were there.