Pterosaurs were the most magnificent fliers of all time. With wings of skin stretched over bone, they soared over the heads of dinosaurs below.
Paleontologists have known about the existence of pterosaurs since the early days of fossil investigation, but researchers are just now getting to know these extinct fliers.
The reptiles are also gaining more attention from the general public. Pterosaurs are often put on exhibit as the "also rans" of the Mesozoic era, presented as window dressing in a world ruled by other, more famous creatures like Tyrannosaurus rex. But this weekend they will fly into the spotlight in the new American Museum of Natural History exhibit "Pterosaur: Flight in the Age of Dinosaurs."
Now is the time of the pterosaur.
Finding the First Fliers
Pterosaurs thrived through the Mesozoic, leaving behind their bones in rocks dating to 228 to 66 million years ago, a time when the planet was populated by dinosaurs and other extravagant ancient reptiles.
The flying creatures weren't dinosaurs, though they were related, having diverged from an older common ancestor to their own evolutionary line more than 245 million years ago.
Naturalists had no idea such animals had existed until the late 18th century. Then, sometime between 1767 and 1784, an unknown person discovered the exquisitely preserved skeleton of the first pterosaur known to science in a layer of 150-million-year-old limestone in Germany.
Italian naturalist Cosimo Collini, who described the fossil, thought that the reptile's elongated fourth finger supported a paddle the creature used to propel itself through the seas. The idea wasn't all that far-fetched: The little animal, named Pterodactylus, was found in stone that formed at the bottom of a lagoon and was filled with marine fossils.
But in 1801, the French naturalist Georges Cuvier realized that those "flippers" were really wings, like those of a bat. That ludicrously long fourth finger supported a membrane that pterosaurs used to take to the sky.
And while Pterodactylus was relatively small—the largest members of the species had only a four-foot (1.2-meter) wingspan—paleontologists were soon digging up stranger, much bigger forms such as the crested Pteranodon, a pterosaur from the Cretaceous period that soared over a vanished seaway on wings stretching 20 feet (6 meters) from tip to tip.
As a group, these animals are properly called pterosaurs. The "pterodactyl" name commonly used by the general public actually applies only to that first critter that Collini described.
Strangely, considering the initial excitement about the flying reptiles, paleontologists soon put pterosaurs aside. "After a lot of early interest, pterosaurs became unfashionable research subjects for much of the 20th century because, among other reasons, their fossils were super-rare and not very well understood at that time," said University of Portsmouth, U.K., paleontologist and artist Mark Witton, who has contributed some of his lavish pterosaur illustrations to the new museum exhibit.
The flying reptiles were seen as "miserable, clumsy, and fragile animals which were little more than early attempts at flight and destined for extinction the moment other flying vertebrates, most notably birds, arrived on the scene," Witton said.
It wasn't until the 1970s, as the whole of paleontology was undergoing a revitalization, thanks to new technologies and evolutionary theories, that paleontologists returned to the study of pterosaurs. They soon realized that the reptiles were far stranger than they ever knew.
"It's widely considered that the early 21st [century] is a new golden age of pterosaur research," Witton said, "with new ideas coming thicker and faster than ever before."
Reptiles Take to the Sky
Pterosaurs flew. That much has been obvious since Cuvier's day. But it has only been in the past decade that paleontologists have sorted out how they actually took flight.
Under old notions about the creatures, "paleontologists tended to assume that pterosaurs either launched using a bipedal run or through gravity-launching from an elevated location," the way some birds and bats do, said University of Southern California, Los Angeles, paleontologist Michael Habib, whose research is highlighted in the AMNH exhibit.
And it's not hard to find old illustrations of Pteranodon hanging upside down from tree branches or cliffs, as if they were giant reptilian bats.
But through detailed studies of biomechanics, Habib has provided evidence that pterosaurs pole-vaulted into the air using a radically different method called quad-launching. Rather than flapping into the air from a standstill, pterosaurs pushed off a surface using both their hind- and forelimbs.
There are several ways to do this, but one especially effective method involves the pterosaur crouching back and then rocking forward on folded wings to give itself a big push into the air.
"This is vastly more powerful than a launch that uses only the hind limbs as the primary launch driver," Habib said. The method would allow the animals to put more muscle behind the launch and would have worked in a variety of habitats. "Even water-launching was probably a modified quad-launch mode in marine pterosaurs," he said.
Flight is only one part of the pterosaur picture. The swell of new research has given these animals a complete overhaul, Witton said.
The flying reptiles were once thought to eat only fish, but "I think we are finally seeing a general acknowledgment that pterosaurs had large diversity in diet and habitat," Habib said.
There were fish-eaters, such as Dorygnathus, which caught the wriggling creatures in spiky teeth. The especially odd Pterodaustro, however, sifted little invertebrates out of freshwater lakes with dozens of tiny, bristle-like teeth. And the biggest pterosaurs, such as Quetzalcoatlus, might have plucked up little dinosaurs in their toothless beaks.
With a fossil record covering 160 million years, it's no wonder the pterosaurs evolved into such a variety of forms. Beyond merely documenting that diversity, paleontologists have been getting a closer look at the details of pterosaur lives.
"We have multiple specimens with associated eggs now, as well as more embryos," Habib said. "We now know quite a bit about the structure of pterosaur eggs, how they must have been laid and incubated, and a bit about early growth."
Those fossils have revealed that nesting pterosaurs buried their leathery eggs to incubate the babies inside, and that pterosaur hatchlings—called flaplings—were probably ready to fly soon after poking their way out of their eggs.
As much as paleontologists have gleaned about pterosaur lives, however, mysteries remain. Scientists are still chasing after the elusive fossils that would illustrate how pterosaurs evolved from superficially lizard-like ancestors, for instance.
"Currently, the oldest, most primitive pterosaurs are already fully fledged flying reptiles with the fully developed flight anatomy which characterizes the group," Witton said.
Connecting those species to their ancestors will depend on future finds. "We need something a little older, and less further along the pterosaur branch, for a conclusive answer," he said.
But such is the nature of paleontology. Every new find creates new mysteries. And given that pterosaurs have recaptured the fascination of scientists and the public alike, their unusual, magnificent forms are certain to fly through our imaginations for years to come.