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Dino-age Flyers Were Sharp-Eyed, Nimble, Study Says

John Roach
for National Geographic News
October 29, 2003
 
Chances were good that prey snared in the sight of a soaring pterodactyl was as good as dead as soon as it was spotted, according to scientists who used sophisticated scanners and computer graphics to digitally reconstruct the brains of the extinct flying reptiles.

"It gives us a window into the behavior of these animals in a way we never thought possible," said Lawrence Witmer, an evolutionary biologist at Ohio University in Athens.


Based on an analysis of the reconstructions and comparisons to alligators and birds, the closest living relatives of pterosaurs, Witmer and colleagues suggest in the October 30 issue of the journal Nature that the ancient flying reptiles had eagle-like eyesight and precision flight control.

These skills, said Witmer, allowed pterosaurs to lock their gaze on prey as they performed complex aerial maneuvers to make the kill.

"The new work clarifies several aspects of pterosaur neural anatomy and prompts some startling new ideas regarding their locomotion and behavior," writes David Unwin, a paleontologist at the Museum of Natural History in Berlin, Germany, in an accompanying article.

First to Fly

Pterodactyls—the common name for pterosaurs—lived alongside dinosaurs during the Mesozoic, about 251 to 65 million years ago. They ranged in size from a few inches to over 40 feet (12 meters) in wingspan and were the first of only three vertebrates to evolve flight.

Birds, close cousins of pterodactyls, are believed to have evolved from theropod dinosaurs about 150 million years ago. Bats are mammals thought to have evolved from shrew-like creatures about 50 million years ago.

Morphologically, pterosaurs were a diverse lot, according to Christopher Bennett, a pterosaur expert at the University of Bridgeport in Connecticut. "They certainly beat out birds on the weird and bizarre scale, what with their extremes of size and large and varied cranial crest display structures," he said.

Scientists have long been intrigued by how pterosaurs flew, but their fossils are rare and often crushed owing to their delicate nature: hollow and lightweight.

Witmer's colleagues, Sankar Chatterjee at Texas Tech University in Lubbock and Jonathan Franzosa and Timothy Rowe at the University of Texas, Austin, recently obtained nearly intact skulls of two pterosaurs: Rhamphorhynchus and Anhanguera.

Rhamphorhynchus had a 3-foot (1-meter) wingspan and 4-inch-long (10-centimeter-long) skull and lived about 150 million years ago in what is now Germany. Anhanguera had a 14-foot (4-meter) wingspan and 20-inch (50-centimeter) skull and lived 115 million years ago in what is now Brazil.

Chatterjee, Franzosa, and Rowe ran the skulls through a high-resolution CT scanner and, with Witmer, reconstructed the brain cavity and inner ear canals.

Flight Control

When the researchers compared the pterosaur brains with those of modern birds, they bore some similarities, but most notably the pterosaurs had an unusually large part of the brain known as the flocculus and large inner ear canals.

The flocculus processes information on body, neck, and head position and relays it via the inner ear canals to eye muscles. This allows an animal to fix its gaze on a target, regardless of its body movements.

"That turns out to be important for an animal that is flying around and moving through space in a complex way," said Witmer.

While previous research noted the unusually large size of the pterosaur's flocculus, Witmer and his colleagues explored why it was so big and what it meant for the creature's ability to fly and hunt.

A key difference between birds and pterosaurs is their wing material. Birds have feathers, which are unfeeling structures, whereas the pterosaur's wings were made entirely out of skin.

This fact, suggest the researchers, may be the reason behind the pterosaur's large flocculus: the pterosaur wing, unlike in birds, could have been linked with the neck, head, and ultimately eye movement to help the flying reptiles keep their gaze locked on prey.

"This large flocculus may go hand in hand with this large, skin-covered flight membrane," said Witmer.

Kevin Padian, a paleontologist at the University of California at Berkeley, said he is not surprised to learn that pterosaurs had sophisticated brains, but that the advances in CT scanning technology give insight that would not have otherwise been possible.

"Everything about their skeletons and their adaptation for flying has always pointed to very active, maneuverable flight," he said. "In fact, I tended to dismiss earlier findings that their brains were small or reptilian for just this reason."

Head Position

The CT scans of the pterosaurs' inner ears also suggest that the larger of the pterosaurs in the Nature study, Anhanguera, may have carried its head in a downward position while Rhamphorhynchus held its head more horizontally.

Scientists say that all animals orientate their inner ear canals in a similar way when they are alert. When Witmer and colleagues created the computer model of Anhanguera, they noticed that its inner ear canals were out of whack.

"So we turned the position of the inner ear to the position it has on the alert and it turns out the head of this animal was strongly down-turned," said Witmer.

Bennett said that the orientation of the semicircular canals in Anhanguera reflect selection for a down-turned "normal" head position, but he is uncertain what a normal posture was for this animal.

"What is unclear is whether that normal posture reflects head posture when the animal was on the ground, or in the air, or when feeding, or none of the above but rather something else," he said.

Witmer and colleagues suggest the down-turned position improved Anhanguera's binocular vision and helped it move on land.

This finding on head orientation, added Witmer, could lead to more studies on head posture in dinosaurs. His earlier work has led to a repositioning of dinosaur nostrils and removed lips from drawings of Tyrannosaurus rex.
 

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