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3-D brain models reveal extinct reptiles

University Of Texas At Austin : 29 October, 2003  (Technical Article)
High-resolution images created at The University of Texas at Austin suggest that pterosaurs lacked the mental capacity of modern birds, but may have been better at in-flight maneuvers.
“Pterosaurs probably weren’t as able as birds today to track prey or to learn the territories of their prey or to predict where to find them, but they did have a finer sense of balance,” said geology professor Timothy Rowe, co-director of the High-Resolution X-Ray Computed Tomography facility in the Department of Geological Sciences.

To determine this, a research team including Rowe scanned the skulls of a 140 million- and an 80 million-year-old pterosaur using a specialized computed tomography scanner designed for examining rocks and fossils. They discovered that the flying reptiles’ brains were smaller than birds overall, but more specialized in the regions that control balance. Those balance-related regions in Rhamphorhynchus muensteri, and the more recent, more advanced pterosaur, called Anhanguera santanae, were about three times larger than comparable regions in birds.

The findings, based on CT scans of skull fossils obtained by co-author Sankar Chatterjee from Texas Tech University, will be published in the Oct. 30 issue of Nature. Rowe analyzed the scans created in Austin with graduate student Jonathan Franzosa, and with lead author Lawrence Witmer from Ohio University.

Other pterosaur fossils had been found previously with fish remains in their body cavities, suggesting that these cousins of the dinosaurs fed by skimming fish off surface waters in lagoons. Rowe noted that this lifestyle likely required more agile flying, and more vision and balance coordination, than required of most birds, which often forage for food on the ground.

An even greater level of specialization was found for the A. santanae specimen, which is thought to have lacked the long tail of R. muensteri to help change directions during flight.

The A. santanae specimen, originally found in Brazil, is believed to have had a protuberance jutting from its bill to help serve as a rudder for directional changes. Image analyses performed by Rowe and his colleagues suggested that the pterosaur also had an even more specialized portion of the brain to help integrate information coming from its wings to stabilize its gaze. And the way it carried its bill compared to its body favored the tougher job of performing front-end steering during flight.

The researchers used the orientation of one balance-related region in the reptile’s skull to determine the angle at which this pterosaur kept its head tilted. As in humans, the animal’s three semicircular canals were likely used to provide three-dimensional input to tell whether it was flying parallel to the Earth. The canal that needed to be level with the Earth in A. santanae would have forced the reptile’s brain to tilt upward, and its long bill to angle downward in relation to its neck muscles. The dropped bill may have assisted with steering during flight.

“As the pterosaurs’ evolutionary history played out and they lost their tails, their head turned into a rudder and their guidance system got even better to accommodate this fundamentally new design of a front rudder,” Rowe said.

So why did pterosaurs go extinct if they had specializations lacking in birds that shared the sky with them some 100 million years ago? Rowe suggested that birds might have won out by having an easier lifestyle and more mental mettle to tackle it with.

“Pterosaurs were probably taking their food on the wing or locating it while flying, which is a more difficult job, and they had a lesser brain to mediate that job,” he said.
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