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