For use in understanding the evolution of vertebrate flight, the early record of pterosaurs and bats is disappointing: Their most primitive representatives are fully transformed as capable fliers.1
The photographs below show that bats have always been bats.
Artist’s impression of a living horseshoe bat. Image courtesy of Steve Cardno).
Palaeochiropteryx tupaiodon—one of the “oldest” (by evolutionary reckoning) fossil bats. It was found in the Messel oil shale pit near Darmstadt, Germany, and is “dated” between 48 and 54 million years old. It clearly had fully developed wings, and its inner ear had the same construction as those of modern bats, showing that it had full sonar equipment. Photo courtesy of Dr. Joachim Scheven.