Pterosaur's Wing, "Hairs" Unlike Any Living Animals'

Charles Q. Choi
for National Geographic News
August 4, 2009
By literally shining new light on a Chinese pterosaur fossil, researchers have found that the membranes in the creature's wings contain a complex pattern of fibers not found in any living animal.

The membrane structure may have given some pterosaur species better control when they took to the skies, a new study says.

The fibers "would have made it easier to make subtle adjustments of the wing membrane when flying, perhaps giving them better flight capability," said study co-author Alexander Kellner, a paleontologist at Brazil's Museu Nacional (National Museum) in Rio de Janeiro.

The well-preserved fossil also included hairlike fibers quite different from the hair on modern mammals.

Similar fibers had been found on pterosaurs before, but researchers had wondered if they were simply products of tissue decay.

(Related: "'Feathered' Dinosaur Was Bald, Controversial Study Says.")

The newly examined pterosaur has the hairlike fibers all over its body and part of its wings. This suggests that the fibers were a covering that may have helped the pterosaurs control their body temperatures, Kellner said.

Soft Tissue and Stone

The fossil pterosaur, Jeholopterus ninchengensis, was discovered in Inner Mongolia in 2000 in a slab of shale loaded with ancient crustaceans and ash.

The stone's age and contents suggest the pterosaur lived roughly 135 million years ago during the Cretaceous period in a region that saw a great deal of volcanic activity.

"This activity might be one of the reasons we find so many fossils in this area," Kellner noted. "The volcanoes would poison the air, and a large number of animals would die."

J. ninchengensis had a broad skull with tiny, peg-like teeth, which suggest the pterosaur fed on insects, he added.

And judging by the long horny sheaths covering its claws, "we think this pterosaur lived at least part of its life in the trees."

The 12-inch-long (30-centimeter-long) pterosaur had a 35-inch (90-centimeter) wingspan—roughly the same as a mallard duck's—with remarkably well-preserved membranes.

"It must have been rapidly buried after it died, perhaps by a river or maybe inside a lake," Kellner said. "Otherwise its soft tissue would have rotted away quickly and not been preserved."

Previous studies of pterosaur wings had shown that each membrane contains a single layer of closely packed structural fibers unique to pterosaurs called actinofibrils. These fibers are thought to have helped reinforce the wing.

When Kellner and colleagues shone ultraviolet light on J. ninchengensis's wings, the team found that the membranes had at least three layers of actinofibrils running in a crisscross pattern.

"This is the first time a wing membrane like this has been reported before," said paleozoologist Eberhard Frey at the State Natural History Museum in Karlsruhe, Germany, who did not participate in this study.

Both Frey and Kellner note that researchers are still trying to find out what pterosaur actinofibrils were made of, which would offer insight into the fibers' exact purpose.

"Were they muscle? Collagen? Keratin? Stiff? Elastic?" Kellner asked.

In general, he said, the new find shows that pterosaur wings are "much more complex than we thought."

Findings will appear in the August 5 issue of the Proceedings of the Royal Society B.

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