When Tyrannosaurus rex was the king of the beasts, the pterodactyl was master of the skies. It was the largest flying creature of all time and it could teach modern aircraft engineers a thing or two. One species had the wingspan of a Spitfire, lightweight bones built like spiral plywood tubing, and wings made of skin less than a millimetre thick that stretched, bat-like, five metres from each fingertip to clawed toe.
For years, this ancient archosaur was considered the aviation ace in evolution's flying circus. But fresh finds of fossil fragments in Mexico, Jordan, Brazil and Texas, suggest that other pterosaur species may have been much bigger.
Scientists say the species would have had wingspans of 18 metres (nearly 60ft) or more, and sailed over warm waters during the Jurassic and the Cretaceous periods, hunting pelican-style for fish.
"They were very, very big animals indeed," said David Martill, of the University of Portsmouth, talking at the British Association Festival of Science in Dublin yesterday.
He demonstrated with a cardboard and cloth model. "This is a five-metre-long wing and there was obviously one on the other side or it would have gone round in circles. We now have evidence that these things were even bigger, maybe twice this size. How did they do that?"
The membrane of the creature's wing was no mere skin: it was a sophisticated tissue that radiated and absorbed heat and controlled airflow. Its bones were phenomenally light weight. Quetzalcoatlus, the Spitfire-sized predator, was discovered in Mexico 30 years ago. But far bigger specimens could soon crop up in the scientific journals, Dr Martill suggested.
"A lot of people argued that Quetzalcoatlus could never have a 10-metre wingspan. Now we actually regard that as perfectly OK and we are expecting to come up with estimates that may be in excess of 18 metres," he said.
How did it fly? "Really rather elegantly. They are exceedingly lightly structured. There is not much body to these animals. They are all wing. It is possible they were flying fairly close to the water to get a little bit more lift by compressing the air between wing membrane and water surface. A few birds use this. Swallows and skimmers use it, but they are very small animals. A few aircraft manufacturers experimented with this, notably the Russians on the Caspian Sea."
The pterosaurs occupied an evolutionary niche somewhere between the ancient dinosaurs, crocodiles and the modern birds. They patrolled the skies for more than 155m years but disappeared with the dinosaurs at the end of the Cretaceous period 65m years ago. They had joints that folded close to the body at the shoulder. The main length of the wing was supported by an elongated finger which could be rotated and folded back. The creature may have hopped like a frog to take off.
Zoologists classify the creatures as dynamic soarers. Like the albatross and condor they took advantage of air thermals to gain height, though they certainly had the muscles for powered flight. Like the modern swift, they may have spent most of their life on the wing, dipping a huge, toothed beak into the water to snap up fish while flying. One species may have filtered the surface water for tiny prey, after the fashion of the modern flamingo.
Nobody has yet calculated the creatures' ground speed. Their development, too, remains a riddle. Evidence from fossil eggs suggests that they could fly straight after hatching. "If this was the case, then it was a remarkable achievement because the wings would have had to have grown from just a few tens of centimetres to several metres without interrupting the animal's flying capability - the equivalent of trying to convert a Eurofighter into a jumbo jet while it was still flying."
Birds and most pterodactyls have wings joined at the shoulder, supporting the body from above. But one fossil fragment found a couple of years ago seemed to show wings joined at the stomach, supporting the animal the way a Spitfire's wings support the fuselage.
How could you tell the size of the new discoveries just from fragments of skeleton?
"Just the sheer size. Even though they are fragments, they are bloody big fragments," said Dr Martill.
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