>>You don't see a lot of natural hot air balloons floating around do you?

Not balloons perhaps, but spiders float on strands of silk using very similar principles.

Pollen and seeds frequently use some kind of floating device to spread as far as possible - again, you probably wouldn't call it flying as such, but they can move through the air for the purposes of reproduction without having wings.

Floating is not controlled flight. Being blown by the wind due to a high surface area to weight ratio is not flight. I move through the air without wings when I walk. I could jump off a diving board and get some forward motion going. Neither are in any way flight.

Anyway, balloons or no, there is a great deal of hot air.

1. Fish do not, in fact, use oil in their livers for buoyancy. They have an "air bladder", which you may read about. You might have heard something, somewhere about shark livers. Fish are much more closely related to you than to sharks, so it is a big error.

2. Buoyancy in air has been achieved with an industrial level of success using hydrogen. Producing hydrogen is easily within the energetic range of biological processes. Air-buoyant animals could have existed for millions, even hundreds of millions of years before being outcompeted by pterosaurs and birds, and then left no trace.

> Fish are much more closely related to you than to sharks

Sharks are fish, so this clearly isn't categorically true. You probably mean either bony fish (for which I think it's kind of questionable that its true) or more specifically lobe-finned fish (for which the case is stronger.)

You miss the point. Humans and bony fish share a most recent common ancestor. We are much closer to the fish than our common ancestor is to the shark.

Um, my point was that that is arguably true of bony fishes, more clearly true of the narrower category of lobe finned fishes, but not at all true as originally claimed of fishes generally, as that includes cartilaginous fishes (including sharks), and sharks are pretty definitively more closely related to sharks than to humans.

In other words, a meaningless statement. In original context, my remark was about fish with air bladders.

It actually, as written, asserted that all fish have air bladders.

“Fish with air bladders do not, in fact, use oil in their livers for buoyancy. They have an ‘air bladder’, which you may read about. [...] Fish with air bladders are much more closely related to you than to sharks, so it is a big error.” is critically different than what you actually wrote upthread, and is obviously kind of silly. It also would have made no sense in response to the post it responded to, which also referenced “fish” in general and not “fish with air bladders”.