I was originally just going to link to a Colugo, which I think are still pretty cool, and probably good evidence of what early stages of vertebrate flight looke

I was originally just going to link to a Colugo, which I think are still pretty cool, and probably good evidence of what early stages of vertebrate flight looked like. Functionally they're not doing full flight like a bat, but their flight is still quite a bit better than a flying squirrel, a sugar glider, or one of the assorted other gliding mammals can do. You can see them flapping. https://www.youtube.com/watch?v=SIgv8Qw--kk https://www.youtube.com/watch?v=SIgv8Qw--kk Like the flying squirrel example given by another poster, they're not closely related to bats. Actually quite closely related to us though. Bats: https://www.onezoom.org/life/@CHIROPTERA=574724 https://www.onezoom.org/life/@CHIROPTERA=574724 Colugos: https://www.onezoom.org/life/@DERMOPTERA=987673 https://www.onezoom.org/life/@DERMOPTERA=987673 Flying squirrels: https://www.onezoom.org/life/@Petinomys=43434 https://www.onezoom.org/life/@Petinomys=43434 Sugar gliders: https://www.onezoom.org/life/@Petauridae=323245 https://www.onezoom.org/life/@Petauridae=323245 But the bat transitional fossils is also an interesting question. And some Googling finds this, which you might enjoy: https://arstechnica.com/science/2008/02/earliest-bat-fossil-reveals-transition-to-flight/ https://arstechnica.com/science/2008/02/earliest-bat-fossil-...