Monday, September 24, 2012

Flight Dynamics of Giant Pterosaurs Explained

Researchers Propose that Quetzalcoatlus Used Cretaceous Runways to Take Off and Land

Scientists from the Museum of Texas Tech University have used computer modelling to assess how the last of the Pterosaurs (flying reptiles) took to the air. Pterosaurs, evolved during the Triassic and they went onto dominate the skies for much of the Mesozoic, until the emergence of the Aves (birds). The very last types of flying reptile were giants, creatures like Hatzegopteryx thambema from Europe and Quetzalcoatlus northropi whose fossils have been found in the Big Bend National Park of Texas. These Pterosaurs were members of the Azhdarchidae and some of these animals were the largest flying creatures known to science with wingspans in excess of ten metres reported. Quetzalcoatlus, for example, had a wingspan greater than that of an American F-16 jet fighter. Seeing this huge animal, many times bigger than the largest birds today, soaring overhead would have been a truly memorable sight. However, how such large and heavy creatures took to the air has puzzled palaeontologists ever since the first fossils of these giant Pterosaurs were discovered.

Creating a Model of Flying Reptile Flight

One University of Texas academic, Sankar Chatterjee (Horn Professor of Geosciences and Curator of the Palaeontology Department at the University's Museum), has suggested that these enormous creatures needed down-sloping runways to enable them to take off. The scientist presented a paper detailing his work on the aerodynamics of Azhdarchidae Pterosaurs at the recent annual meeting of the Geological Society of America in Charlotte (North Carolina).

After a careful, three-dimensional study of Azhdarchid fossils, Professor Chatterjee and his colleagues developed a computer simulation that showed how such an ungainly looking animal would have used a run up in order to gain momentum before finally being able to achieve lift off. Landing would also have been very tricky for these animals, which some palaeontologists estimate may have weighed more than two hundred kilogrammes. When coming into land, the large wings would have acted like giant air brakes, and the Pterosaur would effectively "stall" before touchdown with its hind legs contacting the ground first and then the front of the body and the large head would pitch forward and a quadrupedal stance would be adopted as the flying reptile came to a halt.

Commenting on his research, Professor Chatterjee stated that Azhdarchid Pterosaurs had a similar lifestyle to the modern-day frigate bird or albatross. They could spend a long time in the air with the minimum of effort. However, when it comes to landing and taking off, Pterosaurs would have been very awkward and ungainly. Launching from a cliff top would have been ideal, but where fossils of the Quetzalcoatlus have been found in Texas, these represent non-marine sediments, there were no sea cliffs for these creatures to use. To become airborne a Quetzalcoatlus would have to find a sloping area such as a river bank, a downward slope of just ten degrees would have been adequate. By running, first on all fours and then on two legs, speed could be built up and enough momentum generated to take off. These Pterosaurs needed plenty of room, they needed an area to taxi.

Did Flying Reptiles "Vault" into the Air?

In 2010, a study published in the open access and on line journal "Public Library of Science" proposed that the largest of the Pterosaurs launched themselves into the air by using their strong leg and arm muscles to "vault" upwards. This work was conducted by researchers based at the University of Portsmouth (England). Professor Chatterjee and his colleagues do not agree with these earlier findings. They postulate that such a method of taking to the air may be proven in small bats, but when it comes to a two hundred kilogramme Pterosaur with a wingspan in excess of ten metres; this method of becoming airborne is simply not viable.

Relying on Thermals to Stay Aloft

The Texas based team report that once animals got to a certain size they would not have had the strength and power required to vault into the air. They contend that the only way these large flying reptiles could get airborne would be by taking a long run up, preferably into the wind along a downward sloping bank or similar stretch of ground. Starting on all fours, the animal would quickly switch to a bipedal stance and build up running speed, then just like a modern-day hang glider, it would launch itself into the air, pick up a thermal and rapidly gain height.

Reaching Air Speeds of Over Thirty-Five Miles per Hour

The computer model suggests that these animals could not beat their wings very rapidly. With a high-aspect-ratio wing, similar to that observed today with modern petrels and albatrosses, the Azhdarchid Pterosaurs would rely on thermals and air currents to keep them aloft with the minimum of effort. The animals would have been vulnerable and ungainly on the ground but once in the air they could soar for hours. Professor Chatterjee and his team have suggested that such creatures could attain air speeds in excess of 36 mph (58 kmh).

These enormous creatures, some of which stood taller than a giraffe, were aerial masters, the very last of their kind. Pterosaurs died out at the end of the Cretaceous some sixty-five million years ago. All we have now are their amazing fossils that can be studied so that we can understand how these creatures were able to fly.

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