Flying reptile may have scooped its meals - Skimming the Surface - Brief Article

Science News, July 20, 2002 by S. Perkins

Fossils unearthed in Brazil strengthen the idea that some species of ancient flying reptiles snapped up fish as they swooped low over the water's surface.

The well-preserved skull and lower jaw of the newly described type of pterosaur--Greek for winged lizard--also provide clues about the function of large skull crests sported by many pterosaur species, says Alexander W.A. Kellner of the National Museum in Rio de Janeiro.

Pterosaurs were the first vertebrates, or animals with backbones, to flap their wings and fly. The creatures appeared about 230 million years ago--around the same time as the earliest dinosaurs and more than 75 million years before Archaeopteryx, the first known bird. The delicate, thin-walled bones that minimized a pterosaur's weight and enabled efficient flight didn't usually leave intact fossils.

Kellner and his colleague Diogenes de Almeida Campos of the Earth Sciences Museum in Rio de Janeiro found the nearly complete skull of the new species, estimated to have had a wingspan of 4.5 meters, in a limestone nodule extracted from shale deposits in northeastern Brazil. The fine-grained sediments that entombed the fossils and recorded their rich detail were deposited in shallow, brackish waters about 110 million years ago, the scientists say.

The 1-m-long skull was capped with a hollow, bony crest whose surface is covered with many branching channels, which Kellner and Campos say once contained a network of blood vessels. These channels, the first seen on a pterosaur crest, strengthen the argument that these relatives of dinosaurs used their cranial crests to regulate body temperature. Blood flowing from the brain through the crest would have lost heat as air rushed over the crest's broad surface or gained heat in the morning sun.

A tight sheath of skin would probably have covered the pterosaur's crest, says David M. Martill, a vertebrate paleontologist at the University of Portsmouth in England. Blood vessels nestled within grooves in the crest would have provided a more streamlined outer surface than ones resting atop bone, he notes.

The lower jaw of the pterosaur described by Kellner and Campos also had a large number of blood vessels, which hints that the bill covering the jaw would have been riddled with nerves. The bladelike tip of the lower jaw and the streamlined shape of the upper one suggest that the pterosaur trolled its lower jaw across the water's surface while it glided, the scientists say. As some seabirds do today, the animal would have snapped its jaws shut when it sensed a fish inside them.

Because of its presumed feeding style, Kellner and Campos dubbed the pterosaur Thalassodromeus, which is Greek for sea runner. They describe the creature in the July 19 Science.

The shallow lagoons or seaways over which Thalassodromeus cruised were thriving ecosystems chock full of fish, says John G. Maisey, a vertebrate paleontologist at the American Museum of Natural History in New York who's studied other fossils from the Brazilian sediments.

In the pterosaur's time, the area "was a good place to dine if you were a fish eater," says Maisey.