Life reconstruction of the bizarre membranous-winged Ambopteryx longibrachium. Credit: Chung-Tat Cheungn years ago, it was Ambopteryx longibrachium.
Flight has arisen in vertebrates a few times. Each time, it appeared the exact mechanism was a little different. The The first time was the pterosaur. It used a membranous wing between its body and a digit which became VERY elongated. Next up appeared to be the birds. Derived from theropod dinosaurs, the birds used their feathers in place of membranes to fly. Finally, so we thought, bats developed true powered flight by going back to membranes between almost all their digits on their hands.
We really ought to make sure there was a 'so we thought.'
In the late Jurassic, the relatives of velociraptor were trying out different ways to potentially fly. The successful one was what we know today as birds. However, that was not the only attempt. There was another. The group of dinosaurs we know today as the scansoriopterygidae were experimenting with bat-like wings.
While still having feathers.
Yes, they were weird.
The scansoriopterygids were thought to be climbing theropods. However, in 2015 Yi qi was announced. They had found membranes between the digits much like a bat had. This was somewhat controversial to say the least. These are close relatives to birds' ancestors. One fossil could have been an example of an animal could be a misinterpreted preservation. However, then Ambopteryx longibrachium was found.
With the discovery of Ambopteryx longibrachium and its membranous wings, then it becomes highly unlikely the fossils of Yi qi were being misinterpreted. Ambopteryx longibrachium was found in China and dates from the Oxfordian stage of the Jurassic Period from circa 163 million years ago. This dinosaur was a small theropod, a relative of Velociraptor, Tyrannosaurus and Allosaurus, but much, much smaller.
Theropods ranged from the giants like Allosaurus and Tyrannosaurus down to that small songbird outside your window. It is nearly universally accepted among paleontologists birds are the sole surviving clade (group) of dinosaurs and they are, in fact, very derived theropods. As noted earlier, they fly using their feathers as wings. The scansoriopterygids did not like Ambopteryx and Yi did not. They used membranes like bats and pterosaurs. However, the scansoriopterygids also had feathers.
Ambopteryx longibrachium had long tail feathers like a bird of paradise. These were probably used for displays, much like the extent birds of paradise. However, it's also likely these were also probably used for stabilizing their flights. to see these dinosaurs would have been weird. Their wings like bats and pterosaurs yet fluffy and covered in feathers, even having long tails...of feathers. They would have been wondrous to see though. If small.
If one were to speculate and venture into the world of speculative biology, and assume that birds were delayed for ten to twenty million years, it could be easily seen as these small dinosaurs might have given rise to animals you and I would take for dragons. If dragons had feathers instead of long scaly tails.
New Jurassic non-avian theropod dinosaur sheds light on origin of flight in Dinosauria
https://www.eurekalert.org/pub_releases/2019-05/caos-njn050719.php
A new Jurassic scansoriopterygid and the loss of membranous wings in theropod dinosaurs
https://www.nature.com/articles/s41586-019-1137-z
Pterosaur
https://en.wikipedia.org/wiki/Pterosaur
Bird
https://en.wikipedia.org/wiki/Bird
Bat
https://en.wikipedia.org/wiki/Bat
Scansoriopterygidae
https://en.wikipedia.org/wiki/Scansoriopterygidae
Yi qi
https://en.wikipedia.org/wiki/Yi_(dinosaur)
Oxfordian
https://en.wikipedia.org/wiki/Oxfordian_(stage)
Jurassic
https://en.wikipedia.org/wiki/Jurassic
Bird-of-Paradise
https://en.wikipedia.org/wiki/Bird-of-paradise