How Did Pterosaurs Fly?

 

Visit the exhibition to experiment with principles of pterosaur aerodynamics in an interactive virtual tunnel.
© AMNH/D. Finnin

Flight allowed pterosaurs to travel long distances, exploit new habitats, escape predators, and swoop down from above to seize their prey. They spread across the world and branched out into an enormous array of species, including the largest animals ever to take wing.

BUILT TO FLY

Like other flying animals, pterosaurs generated lift with their wings. They needed to perform the same kinds of motions as birds and bats, but their wings evolved independently, developing their own distinct aerodynamic structure.

Nemicolopterus crypticus was recently discovered in northeastern China, in a region once dotted with wetlands, lakes, and forests. This tiny pterosaur may have darted through forests hunting for insects.
© AMNH 2014

Pterosaurs flew with their forelimbs. Their long, tapering wings evolved from the same body part as our arms. As pterosaurs’ arm and hand bones evolved for flying, they lengthened, and the bones of one finger—the equivalent of our ring finger—became extraordinarily long. Like the mast on a ship, these bones supported the wing surface, a thin flap of skin that was shaped like a sail.


WING BONES

Although many animals can glide through the air, pterosaurs, birds, and bats are the only vertebrates that have evolved to fly by flapping their wings. All three groups descended from animals that lived on the ground, and their wings evolved in a similar way: their forelimbs gradually became long, bladelike, and aerodynamic.

The medium-sized Istiodactylus evolved during the Cretaceous, and its contemporaries included the largest flying animals ever known, such as Pteranodon longiceps and Quetzalcoatlus northropi.
© AMNH 2014

Large pterosaurs needed strong limbs to get off the ground, but thick bones would have made them too heavy. The solution? A pterosaur’s wing bones were hollow tubes, with walls no thicker than a playing card. Like bird bones, they were flexible and lightweight, while strengthened by internal struts.

INSIDE THE WINGS

Recent discoveries show that pterosaur wing membranes were more than simple flaps of skin. Long fibers extended from the front to the back of the wings forming a series of stabilizing supports, so the membranes could be stretched taut, or folded up like a fan. Separate muscle fibers helped pterosaurs adjust the tension and shape of their wings, and veins and arteries kept the wings nourished with blood.

Rhamphorhynchus's long tail had a stiff flap of skin called a vane at the end that stabilized flight. Some scientists think this membrane faced sideways, like a fish tail, and helped prevent rocking from side to side. Others think it lay flat, like a paddle, and helped the flying pterosaur control its elevation.
© AMNH 2014

The exhibition includes a remarkable fossil of Rhamphorhynchus muensteri, discovered in Germany in 2001, which features wing tissues so well preserved that scientists have been able to see fine details in their structure. Under ultraviolet light, researchers detected layers of skin threaded with blood vessels, muscles, and long fibers that stiffened the wing. Because of the shadowy color of the wing membrane, paleontologists call this fossil Dark Wing.

The Pterosaurs exhibition includes a remarkable fossil of Rhamphorhynchus muensteri known as Dark Wing, which has allowed scientists to see fine details of pterosaur wing structure.
© AMNH/D. Finnin


See more at the Natural Museum of History

Toothless 'dragon' pterosaurs once ruled skies

Ancient winged reptiles called pterosaurs were so successful that they ruled Earth's skies for tens of millions of years, according to a study published in the journal ZooKeys.

The fearsome fliers, part of a family of pterosaurs named Azhdarchidae, get their name from azdarha, the Persian word for "dragon." Unlike earlier pterosaurs, they had no teeth, and they dominated from late in the Cretaceous period (around 90 million years ago) until the extinction event that also killed off the dinosaurs some 66 million years ago.

“This shift in dominance from toothed to toothless pterodactyloids apparently reflects some fundamental changes in Cretaceous ecosystems, which we still poorly understand,” study author Alexander Averianov of the Russian Academy of Sciences wrote in the paper.

Pterosaurs are not dinosaurs, and they're definitely not ancient birds, which are the living descendants of the dinosaurs. But understanding these large predators can give insight into the ancient ecosystem as well as the origins of flight, as pterosaurs are thought to be the first animals after insects to develop powered flight.

Pterosaur fossils are tough to find, the study authors point out, because their fragile bones haven’t survived as well as dinosaur remains have.

“Pterosaur bones were thin and fragile, much like bird bones, and they often drifted apart, shattered, or became scrambled before they could be preserved,” according to the American Museum of Natural History.

Thus, it’s often pretty difficult to tell how the few fossils that do exist are related to one another, according to the paper.

“Azhdarchidae currently represents a real nightmare for pterosaur taxonomists: Most taxa are known from few fragmentary bones, which often do not overlap between named taxa, the few articulated skeletons are poorly preserved,” Averianov wrote, and some of the best material “has remained undescribed for 40 years.”

For the ZooKeys study, Averianov surveyed and analyzed the known research to help straighten out the fossil record. The findings also showed that although their bones are challenging to find, the pterosaurs were probably quite successful in a wide variety of habitats, but were more commonly found near large lakes and rivers and especially in near-shore marine environments.



Reposted Copyright © 2014, Los Angeles Times