AFLUTTER is the only way to describe the crowd gathered in Las Vegas on November 2nd-5th for the annual meeting of the Society of Vertebrate Paleontology. The source of the commotion was not a paleontologist's stonking win in one of the city's casinos. Nor was it that paleontological favourite, dinosaurs. (Though, as we report in twoarticles in this week's print edition, they too caused a fair bit of excitement.) Rather, it was a challenge to the discipline's long-held belief that flapping wings, with their complicated nerve, muscle and bone structure, must, surely, have evolved from a simpler variety that allowed its owners to glide.

Kevin Padian, of the University of California, Berkeley, and Kenneth Dial, of the University of Montana, Missoula, arrived at their startling (to paleontologists) conclusion after poring over the bat family tree. Typically, if a trait evolves into another, it leaves behind a trace in a species' fossil record. Alternatively, the species' living relatives might have retained it. Finding a gliding bat, fingering the anatomical features which contribute to gliding ability, and then discovering similar features in the fossilised remains of the two species' most recent common ancestor would therefore be a hint that today's flapping bats glided before they flapped.

At first, Dr Padian and Dr Dial were expecting to find fossilised bats that were gliders, not flappers. To their surprise, they discovered nothing of the sort. They then expanded their search to all flying and gliding animals. What they found was, if anything, even more shocking: gliding and flapping fauna appear to have no direct common ancestor. This suggests that the prevailing theory is wrong. It also, however, leaves open the question of where powered flight comes from.

Dr Padian and Dr Dial think that here, too, bats offer a clue. They noticed that the earliest animals that could definitely be identified as bats were capable climbers which fed exclusively on insects. Unlike modern bats, though, their bodies lacked the telltale bony structures that would permit them to echolocate flying prey. And since they lived in caves, they would have a tough time using their sight to hunt for tiny insects, as many birds do in the daytime. (Contrary to received wisdom, bats are not blind.) As such, the researchers speculate, their diet would probably have consisted mainly of crawling insects. Yet this idea seems at odds with another well-established fact about those early bats. If they fed on crawlies, why would they spend much of their time perched high up on cave walls, where such meals would be few and far between?

The researchers hit on a possible answer while watching video footage of a baby bat being dropped off a ledge. The creature rapidly fluttered its wings in a desperate attempt to arrest the fall, much as a fledgling bird would. This led Dr Padian and Dr Dial to propose that ancient bats' hunting strategy consisted in clambering up high, hanging upside down and dropping to ambush crawling insects from above, making correcting flaps with proto-wings as they fell.

It did not take long for the idea to take off. After Dr Padian's and Dr Dial's presentation, other experts present in Las Vegas noted that although most bats hunt on the wing and do not ambush prey, a handful of species behave in much the same way the duo are suggesting. They hang quietly, listening for the sounds of insects landing on leaves, and swoop down to bite them. The evidence is still far from conclusive. But the idea that flapping wings did not start out as a gliding aid is no longer a flight of fancy.