How Pterosaurs Might Inform the Next Generation of Flight

On May 17, 1986, the Smithsonian National Air and Space Museum unleashed its flying reptile at Andrews Air Force Base. Known as Q.N. to the engineers and experts who created the flyer, the model was a half-size replica of the immense pterosaur Quetzalcoatlus northropi that had just been discovered a decade before. Technically called an ornithopter, because it was meant to be birdlike in the way it flew, Q.N. was a mock-up with an 18-foot wingspan. “We had to go through the evolutionary cycle in our development just like nature did. But we were going about a million years a week,” project leader Paul MacCready told the Los Angeles Times earlier that year. Q.N. had chewed through $700,000 in funding and staggered through a series of crashes before the flapping aircraft was finally ready to fly.

More than 300,000 people gathered at the air base, ready to see a pterosaur—or something pterosaur-like—take to the air for the first time in 66 million years. The reptile-like flying machine had done just fine out in the arid desert of Death Valley, where it was filmed for the IMAX movie On the Wing, so a tour around Andrews seemed simple enough. But crowds may have left the event wondering how such animals could have taken to the air in the first place. Soon after being released from a tow line used to get Q.N. into the air, the mechanical pterosaur began to spin and turn so sharply that the faux-reptile’s neck snapped and it crashed, headless, to the ground.

Despite Q.N.’s public embarrassment, however, the ornithopter’s inspiration has lived on. In the early 1990s, when Q.N. was still in storage at the Smithsonian National Air and Space Museum, curator Russell Lee made the case that the pterosaur should be accessioned into the collection as an important part of aviation history. “A lot of thought and effort went into developing this thing,” Lee says, adding Q.N. was a state-of-the-art aircraft despite its failure. And now, the spirit of Q.N. lives on as experts are going back to these ancient creatures to find new ways to fly, from aircraft with pterosaur-like crests to pterosaur-inspired spacecraft exploring the nooks and crannies of Mars.

---

Despite the family resemblance, pterosaurs were not dinosaurs. Rather, they were close evolutionary cousins of the dinosaurs that shared many of the same biological hallmarks. A hot-blooded metabolism, bodies covered in multicolored feathers and lightweight bones assisted the rise of the pterosaurs at the same time that dinosaurs were beginning to stalk around on land around 243 million years ago. But what makes pterosaurs immediately distinctive are their wings.

The wing of a pterosaur was much more like a bat’s than a bird’s. Pterosaurs all shared extremely elongated fourth fingers—the equivalent of your ring fingers—that could be longer than the entire rest of their bodies. These hyper-elongated digits supported thin membranes that connected to the reptile’s sides and legs, sometimes with some accessory membranes attached between the legs and hips. Even though pterosaurs also had feathers on their heads, necks and torsos, they relied on these leathery wings to get aloft. But how they used their membrane-based wings stumped paleontologists for nearly two centuries.

Pterosaurs were so unlike any living animal that naturalists didn’t initially know what to do with them. “The first pterosaur was found before things like ichthyosaurs and plesiosaurs, and was so different from anything we’d ever seen,” says University of Bristol paleontologist Liz Martin-Silverstone. In 1784, Italian naturalist Cosimo Alessandro Collini was so confused by the anatomy of pterosaurs that he thought the animal was a swimmer, not a flyer. He proposed that the long fourth finger on each arm supported a paddle for pushing itself around ancient waterways. Not until 1800 did experts start to realize that pterosaurs flew, and even then experts were divided on whether pterosaurs were reptiles or were more like strange ancient bats. The various hypotheses were all based on individual finds that experts had no context for, until 1834, when the word “pterosaur” was finally coined by German naturalist Johann Jakob Kaup for what experts finally agreed were bizarre flapping reptiles.

So pterosaurs were reptiles, and they flew. But how? The more experts learned, the stranger pterosaurs became. They could envision how a small one, like the snaggle-toothed Rhamphorhynchus—might flap into the air just as birds do. The creature was about the size of a raven. But discoveries in the United States, especially, indicated that other pterosaurs were far larger than anything else that ever flew. These reptiles were bigger than bustards, bigger than albatrosses, and in 1975 paleontologist Douglas Lawson described what may be the largest flying animal of all time—Quetzalcoatlus, a pterosaur that stood as tall as a giraffe on the ground and had a wingspan 36 feet across. “The biggest birds that ever flew were quite a lot smaller than a big pterosaur,” says Martin-Silverstone, and that disparity raised a litany of new questions about how the animals flew.

Imagining a Quetzalcoatlus just fluttering into the air seemed ridiculous. And thinking of the pterosaur like a big bat or bird didn’t offer much clarity, either. If they hung from cliffs—à la the pterosaurs in Fantasia—that would have required quite a lot of seaside cliffs of just the right height and composition to support populations of such animals. Likewise, Quetzalcoatlus probably wasn’t using a long runway like Orville the albatross in The Rescuers. That would have called for multiple long, flat, unbroken open areas free from harassment by Tyrannosaurus upon departure. There’s no indication such pristine, perfect-for-takeoff pterosaur runways existed. On top of that, all known footprints and trackways made by pterosaurs show that they were quadrupedal animals, awkwardly shambling around on all fours while on the ground. A pterosaur walking on all fours, wings folded, wouldn’t have been able to move fast enough to achieve takeoff speed.

These complications led some paleontologists to suggest that maybe big pterosaurs didn’t fly at all, a point reinforced by faltering efforts to recreate the success of these fanciful flyers. Q.N. was part of the repeated attempts to recreate airborne pterosaurs that proved to be more complicated than initially expected.

But paleontologists have been persistent. Understanding pterosaur takeoff is critical to comprehending the biology of the extinct reptiles. Pterosaurs must have had some other method of getting off the ground. In 2008, after researching what had been done before and what pterosaurs might be capable of, University of California, Los Angeles, paleontologist Michael Habib proposed that pterosaurs used a unique technique called quadrupedal launch, or quad launch. Think about it like this. A happy little pterosaur is shuffling around on the ground with folded wings. All of a sudden a predator gets too close—the creature needs to take off. Standing in place, the pterosaur shifts its body weight backward and then, using its folded arms like pole vaults, pushes itself into a leap and throws open its wings. The powerful jump gave the pterosaurs enough momentum that flapping could get them airborne, each beat of their wings continuing to carry them through the air whether they were as small as a woodpecker or as large as a fighter jet.

Crunching the numbers involved—how much pterosaurs weighed, the surface area of their wings and other variables—Habib found that quad launching would have worked for pterosaurs of all sizes, up to 600 pounds. The little ones could have used the technique just as the big ones could. What’s more, the concept also seemed to work on the water—solving the mystery of how big pterosaurs like the toothless Pteranodon could nab fish in the middle of the ancient sea and then get back into the air instead of having to paddle all the way back to the coast. Some pterosaurs found in rocks laid down by ancient oceans even show signs of little soft tissue extensions off their feet, a way to increase surface area and help them launch themselves from the water at a moment’s notice.

---

Humans have always been fascinated by how other organisms fly. We have long tried to reverse-engineer what other creatures evolved to do, from the wax and feather wings in the story of doomed Icarus to the Wright brothers reading up on the details of bird flight prior to their historic liftoff at Kitty Hawk, North Carolina, in 1903. An entire subfield of engineering often referred to as biomimicry or bioinspired design takes lessons directly from bird feathers, insect wings and even pterosaur membranes. And the strangeness of pterosaurs makes them particularly interesting.

Paleontologists Elizabeth Martin-Silverstone, David Hone and Habib suggest the flying reptiles might present unique solutions to aerodynamic problems that evolution solved millions of years ago. Understanding the way pterosaurs flew requires, for example, modeling the membranes of tissue their wings were made of, an aerodynamic puzzle that has piqued the interest of the Army Research Lab as well as paleontologists. “Pterosaurs evolved to do things birds and bats have not done,” Habib notes, such as taking off almost vertically. They also reached far larger sizes than any other fliers, comparable to some modern aircraft in wingspan, so study of the long-lost reptiles could inform lighter, sturdier designs.

“If we have something with a different morphology, why not try that? They must have been doing something right,” Martin-Silverstone says. And so she, Habib and colleagues across the Smithsonian, NASA and beyond have been pondering how pterosaurs might change what we engineer.

Big pterosaurs evolved to fly at large size while remaining light, and they could take off and land in constrained spaces, abilities directly relevant to aerospace design. The anatomical solutions pterosaurs evolved to prevent their wing membranes from tearing, Habib notes, can be applied to aircraft like quadcopters, four-rotor drones. The rotors need to be thin, move at high speed, and resist tearing while in motion, a combination of characteristics that pterosaur wings can help inform.

And in one Carnegie Mellon project funded by NASA, Habib says, the engineering team wanted to come up with a complete alternative to drones that use rotors to fly over the surface of Mars. Rotors have to be very large to generate enough lift for the drone, so it can be difficult to maneuver rotor-based drones in tight spots like a particular crater planetary scientists might want to investigate. “Flapping wings work well on Mars,” Habib suggested, especially because gravity is lower on the Red Planet. So the team worked on a pterosaur-based design, capable of landing in a small space, quad-launching away and flapping to the next site.

Tents, of all things, have as much to benefit from pterosaurs as drones fitted for Mars exploration. The membranes of pterosaur wings had to stay strong and resist tearing while staying thin, even at high wind speeds. The shape and composition of their wings were able to overcome what’s called the “aeroelastic problem,” or the tendency of soft, pliable wings to shake at high speeds. If a tent’s frame and rain fly could be modeled after pterosaur wings—with the proper materials—then tents for field teams or film crews in harsh locales could better withstand windstorms that might damage the camp. “Pterosaurs had to evolve a bunch of solutions to this aeroelastic problem,” Habib says, which might now be helpful in preventing human-made materials from shredding under high winds.

Not everything informed by pterosaur anatomy is necessarily going to look like the prehistoric animals. “A quad-launching drone would look like a pterosaur,” Habib says, “but there are other more subtle things.” This may be hard news for those who fondly remember the pterosaur-based “Transformers” character Swoop.

But while paleontologists and engineers aren’t necessarily focusing on pterosaur lookalikes like Q.N. anymore, Habib notes, they’re still deeply interested in what pterosaurs might teach us. Evolution, after all, molded pterosaurs to solve many of the same problems we now contend with as we seek to take to the skies and explore other worlds.

Full credit for second image: Mark Witton and Darren Naish; Witton M.P., Naish D (2008) “A Reappraisal of Azhdarchid Pterosaur Functional Morphology and Paleoecology.” PLOS One 3(5): e2271 via Wikipedia under CC By-SA 3.0

Riley Black | | READ MORE

Riley Black is the author of The Last Days of the Dinosaurs and many other books. She is a science correspondent for Smithsonian magazine covering fossils and natural history, and she writes about the prehistoric past for a variety of publications.