Smart Wings of the Jurassic

Evolution is nature's great R&D division. Through mutation, natural selection, and other processes, life can find new solutions for the challenge of staying alive. It's possible to see a simplified version of this problem solving at work in the lab. The genetic molecule RNA, for example, can evolve into shapes that allow it to do things no one ever expected RNA to do, like join together amino acids. Over millions of years, evolution can solve far bigger problems. How can a mammal became an efficient swimmer? How can a bug fly?

Humans would like to build ocean-going vehicles as efficient as dolphins, and miniature robots as efficient as flies. For these and many other wish-list items, researchers are turning to the products of evolution for inspiration. Last year in Popular Science I wrote about one of the most interesting people doing this kind of work right now, the Macarthur genius grant winner Michael Dickinson of CalTech. Dickinson is figuring out how flies fly. It's surprising that they can fly at all, actually, since simple engineering calculations would suggest that they can't even get off the ground. But those calculations are based on our own crude notions of aerodynamics. When it comes to flight, it's hard to imagine a world beyond fixed wings. Dickinson has shown that by continually adjusting their wings with tiny tilts and twists, flies take advantage of various loopholes in the laws of aerodynamics. They don't need a supercomputer to figure these movements out. In fact, they actually have only a few thousand neurons. Their flight algorithms are installed in their anatomy with an elegant simplicity that humans can only ape. (Dickinson is now involved in a project to build insect-sized robots based on the principles he's uncovered.)

Evolution has found at least three other solutions to the problem of flight. Birds and bats can fly, birds with airfoils of feathers, and bats with the webbing between their fingers. Evolution's third solution disappeared over 65 million years ago. Pterosaurs, close relatives to dinosaurs, had hands that stretched out into absurdly long spars. Draping down to their feet were two sheets of membrane that they flapped, creating lift. It's a solution so weird that you might doubt that it could really let an animal fly. But pterosaurs thrived for some 150 million years, taking all kinds of forms that foreshadowed today's birds--from little pigeon-sized flappers to flamingo-like lake-feeders to gigantic soaring species the size of small planes.

We can't watch pterosaurs in flight, but their fossils preserve a few clues about how they managed to stay airborne. In Nature today, a team of paleontologists described the shape of pterosaur brains. While their brains rotted away long ago, some pterosaur skulls are preserved well enough to show the shape of the brains they contained. The scientists scanned the skulls and then reconstructed the brains, comparing them to birds, dinosaurs, and other animals. One important thing they found was that regions called the floccular lobes (located in the back of the brain) were huge compared to birds or mammals. These lobes may have helped pterosaurs stay balanced, because they take information in from the semi-circular canals of the ear. But they are also involved in the brain's awareness of the body--otherwise known as proprioception. As paleontologist David Unwin points out in an accompanying commentary, proprioception may have been a crucial sense for pterosaur flight. New fossils show that pterosaur wings were not just simple sheets of tissue, but have lots of muscles and even tendons running through them. It's possible that pterosaurs could make lots of fine adjustments to the shape and angle of their wings by tightening or loosening different patches of them (a fine-tuned strategy that reminds me of the tricks of insect flight). Big floccular lobes would be necessary to keep these complex wings under control.

What makes this new research particularly interesting at the moment is an article in the current issue of Popular Science by Carl Hoffman about engineers who are trying to build "smart wings" for airplanes. These wings would be embedded with sensors that could detect the changing air flow around them, and could respond by altering their shape on the fly (sorry). Smart wings could make planes faster, nimbler, and more efficient. The engineers profiled in the article take birds as their model, but when you think about it, bird wings are pretty remote from what they have in mind. The engineers do not plan on building wings out of giant feathers. The flat sheets that pterosaurs used are a far better analog. And the new research on their fossils suggests that they may have been remarkably smart wings at that. Aeronautical engineers would be well advised to invest in some rock hammers.


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