There was a prehistoric period on Earth before bugs and birds evolved when the only living creature that could fly were terrestrial/atmospheric jellyfish which flew the same way dirigibles fly, they created their own supply of lighter than air gas by separating hydrogen from water and for ages they filled the sky beautifully, but then flying predators evolved and that was the end of that. No fossil record exists of them because they didn't have body parts that were conducive to fossilization, they were all soft tissue. This being the case, there are unfortunately no images to represent this era of life on Earth so pic is unrelated.