Flying reptiles give up secrets

Pterodactyl: The prehistoric hunters had an impressive system of flight instrumentation.

Medicine & Science

November 03, 2003|By William Mullen | William Mullen,CHICAGO TRIBUNE

Pterodactyls, the fierce-looking flying reptiles that thrived in the days of dinosaurs - some with wingspans as wide as a Learjet's - came equipped with flight instrumentation that should make 21st-century aeronautical engineers envious.

A team of American paleontologists used industrial-strength CT scans to capture the first pictures of the inside of the braincase of two species of pterosaurs, the creatures popularly known as pterodactyls.

Paleontologists hail the pictures as a breakthrough, revealing how the earliest flying vertebrates developed an extraordinary physiological apparatus that made them more sophisticated and efficient fliers than today's birds and bats.

The findings, published in the British science journal Nature, are part of a growing body of research giving scientists a much deeper, entirely different idea of how the reptiles flew.

A team headed by Lawrence Witmer, a professor of anatomy at Ohio University Osteopathic Medical College, used CT scans of the two pterodactyl skulls to study tiny inner-ear canals and outsized brain lobes (the flocculus) that link brain activity with body movement. Birds and bats also have a flocculus, but in pterosaurs, they're much bigger relative to the rest of the brain.

Witmer's research centered mostly on how pterodactyls performing aerial maneuvers kept their eyes focused on prey on the ground or in the water.

But David Unwin, a Humboldt University paleontologist in Berlin, has linked Witmer's findings to recent discoveries of complex muscle structures in pterosaur wings, so sensitive that the wings acted almost like sensory organs.

Witmer said that as a pterodactyl soared through the air, sensitive muscle fiber near the surface of the skin on its wings sent continuous streams of data on wind speed, temperature, body attitude, position and tension of wings to the brain through the flocculus.

The brain could then send instructions back to the pterodactyl's wing through the flocculus, changing the tension on the skin, causing subtle changes in the shape of the wings to alter flight speed or direction.

"It is an amazing structure," Unwin said. " ... They pushed the envelope aeronautically. Birds certainly don't have that sort of thing. Maybe bats have this, but nobody has looked, so far as I know."

Like their relatives the dinosaurs, pterodactyls were one of Earth's most successful life forms, surviving 140 million years. They evolved from lizardlike creatures 200 million years ago and disappeared with dinosaurs 65 million years ago.

Fossils of about 100 pterosaur species have been discovered, ranging from creatures the size of a sparrow to the Azhdarchid, with a wingspan of 40 feet. Pterosaurs were carnivorous, with most preying on fish.

Scientists knew that the flocculus in pterosaurs was much larger than in birds and bats, but Witmer said he wanted to find out why.

For several years, paleontologists have used industrial CT scans of fossilized bones - particularly skulls - to look for tiny anatomical structures.

The soft tissue of organs is gone, but the telltale bone cavities that once contained the organs, even tiny inner-ear structures, remain intact in fossil skulls. Medical CT scans usually are not powerful enough to detect those cavities, but they can be picked up by industrial equipment used to examine huge pieces of machinery for tiny cracks and flaws.

Intact pterosaur skulls are extremely rare. As flying animals, their bones were hollow, delicate and very light. Unlike heavier dinosaurs, few sank into the mire that made fossils. Those that did were usually broken and squashed by geologic forces.

Witmer managed to borrow two intact pterodactyl skulls from museums, a 4-inch-long skull of a crow-size species called Rhamphorhynchus that lived 150 million years ago in Germany, and the 20-inch skull of a species called Anhanguera with a 14-foot wingspan that soared over Brazil 115 million years ago.

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