LibriumArcana.Games

Lizard ancestor spread its ribs to glide

By Roger Highfield, Science Editor
Last Updated: 12:01am BST 15/07/2008

Long before the first birds took to the skies, this ancestor of the lizards spread its ribs to glide from tree to tree, or to parachute down to a soft landing.

The British beast, called Kuehneosaurus, lived 225 million years ago and was flitting about long before Archaeopteryx, the world's oldest bird, which flew some 150 million years ago.

A new study of the extinct ancestors of reptiles by scientists from the University of Bristol, shows that these early flyers used extraordinary extensions of their ribs to form large gliding surfaces on the side of the body. The results are published today in the journal Palaeontology.

Kuehneosaurs, some up to two feet long, were first found in the 1950s in an ancient cave system near Bristol.

Their lateral 'wings' were always assumed to be some form of flying adaptation, but their aerodynamic capability had never been studied.

Koen Stein, who did the work while a student at Bristol, has shown that of the of the two groups of species found in Britain, Kuehneosuchus was a glider (it has elongate 'wings'), while Kuehneosaurus, with much shorter 'wings', was a parachutist.

As the two forms are so alike in other respects, it is possible that they are males and females of the same animal.

Stein said: "We didn't think kuehneosaurs would have been very efficient in the air, but all the work up to now had been speculation, so we decided to build models and test them in the wind tunnel in the Department of Aerospace Engineering at Bristol.
advertisement

"Surprisingly, we found that Kuehneosuchus was aerodynamically very stable. Jumping from a five-metre tree, it could easily have crossed nine metres distance before landing on the ground. The other form, Kuehneosaurus, was more of a parachutist than a glider."

So that Stein and his colleagues could work out how these creatures controlled their flight they had to model different skin flaps over the wing area.

"We also built webbed hands and feet and had an extra skin membrane between the legs on the models, but these made the flight of the animals unstable, suggesting that they probably did not have such features," said Stein, who now works at the Institut für Paläontologie, Bonn,

Most animals with the ability to glide, such as "flying" frogs and squirrels, remain airborne with the help of a membrane spread between their toes, or between body and legs.

Ribs are not just used by Kuehneosaurus but by a more recent - 130 million years old - six inch gliding lizard fossil (Xianglong zhaoi) found in northeastern China, with its most striking feature the elongated ribs that helped to spread a wing-like membrane for gliding.

The rib-supported gliding membranes arose by convergent evolution, the process by which different species come up with the same solution to the same problem, in this case how to glide, said Prof Michael Benton, a member of the research team and Head of Department in Bristol.

"Palaeontologists are keen to understand how all the amazing animals of the past operated and by collaborating with aerospace engineers we can be sure that model-making and calculations are more realistic."

LadyTevar wrote:There is a modern lizard that does this as well, isn't there?

I wonder how they avoided damage from getting hit on the bottom of their body. Wouldn't their internal organs be awfully squishy without a ribcage to protect them? Or am I missing something?