Pterosaurs 'flew like birds'

By Julianna Kettlewell
BBC News Online

The pterosaur Anhanguera had a downward pointing head

Pterosaurs were not cumbersome gliding dinosaurs, but nimble and athletic flyers, scientists now believe.

The ancient reptiles, which flourished 251 to 65 million years ago, might even have outperformed modern birds.

Researchers examined 3D images of their brains and found the regions relating to balance were particularly pronounced - suggesting pterosaurs would have been agile swoopers and divers.

The findings are published in the journal Nature.

Conventional wisdom

Ranging in size from a sparrow to an aeroplane, pterosaurs dominated the skies between the Jurassic and Cretaceous Periods.

They were four-limbed animals with membranous wings that stretched between their front and back legs.

Anhanguera probably had an upright posture

It was once thought that pterosaurs were not well adapted to active flight, and it was quite a haul for them to get off the ground at all.

If conventional wisdom was to be believed, they relied on thermals to stay aloft, having clumsily plopped off the edge of a cliff.

But the discovery of new evidence might have put that theory to rest.

Bird brained

Researchers, led by Lawrence Witmer from Ohio University, US, studied a pair of pterosaur skulls and generated three-dimensional reconstructions of their brains.

This was possible because pterosaur brains are nestled so tightly in their brain-cases that they leave a bony impression, betraying their structure.

There is this idea that pterosaurs were failures because they are extinct, but that is temporal chauvinism David Unwin, Natural History Museum, Berlin

Overall, the brains were very bird-like. For example, they had reduced olfactory lobes and large optic lobes, which suggest that, like modern birds, they were more interested in what they could see than what they could smell.

But there was one surprising difference in the pterosaurs: two balance related regions, called the floccular lobes, were very pronounced.

These may have gathered information from the sensitive wing membranes, and helped the reptiles build up detailed maps of the forces experienced by their wings, giving them excellent flight control.

"They recruited the wing as this extra sensory organ and linked it with the neck, head and ultimately eye-movement," Lawrence Witmer said. "This means the body can change position but the eyes can stay focused on their prey."

A creature endowed with such skills could become a highly adapted, visually oriented flying predator. Pterosaurs may have lived over the ocean, surviving on fish nimbly plucked out of the water.

3D images were made using fossilised skulls

"We in the pterosaur field have suspected for a long time that they were good flyers - that they hunted fish and insects while flying - and now that has been confirmed," David Unwin, of the Natural History Museum in Berlin, told BBC News Online.

"But the surprising thing is that they had such smart wings. The wing membranes are very structured and can send back complex information - they are not just leathery skin."

As for the idea that pterosaurs could not leave the ground without jumping off something tall, Dr Unwin discredits it enthusiastically.

"Their wings were so large that, relatively speaking, wing load was low," he said. "If a pterosaur spread its wings, staying on the ground would have been more of a problem than taking off. Any gust of wind would have lifted them up."

Jaunty head

One of the pterosaurs studied with 3D imaging - the large, short tailed Anhanguera - may have carried its head at a jaunty angle, the researchers have said.

The orientation of one balance-related organ suggests that Anhanguera's head was probably directed downwards at a sharp angle of 30 degrees.

This could tell us something about how the animal walked when it was on the ground.

"Their body while on the ground would have been carried at an almost vertical angle - so that is why their head needed to point down," explained Dr Unwin.

Pterosaurs were successful residents of the Earth for 150 million years, which is the same amount of time that modern birds have been around.

Dr Unwin said: "There is this idea that pterosaurs were failures because they are extinct, but that is temporal chauvinism."