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So far, so good. The trouble starts when scientists try to extrapolate patterns of behavior and locomotion from the fossil evidence. At last week's meeting, for example, scientists debated whether pterosaurs walked on two legs, like birds, or crawled on all fours, like bats. Hundreds of footprints discovered at dozens of sites in the U.S. and Europe over the past few years, argues Martin Lockley of the University of Colorado at Denver, strongly support the latter conclusion. The pattern of these footprints, which range in size from 1 in. to 5 in., suggests that pterosaurs held their bodies in a semierect position, with their long wings folded back so that their clawlike fingers gripped the ground.
Berkeley's Padian, on the other hand, contends that pterosaurs did not have to walk on their wings, but were agile two-legged runners. He also disagrees with the explanation University of Bristol paleontologist David Unwin offers for the long fifth toe that juts out from pterosaur hind limbs. Unwin believes this toe served as the attachment site for a second skinlike membrane that stretched between the animals' hind limbs. "Why else would the fifth toe have been so elongated?" he asks. Padian responds that Unwin's membrane does not make anatomical sense: among other things, it would have hampered pterosaurs' ability to move on the ground.
Endless debate also swirls around the question of how pterosaurs managed to become airborne. Some scientists think the beasts launched themselves from a running start, while others believe they were so clumsy on the ground that they would have had to drop from cliffs or trees to attain a flightlike glide. Lockley, for one, argues that pterosaurs had to be capable of birdlike takeoffs and landings if only because so many pterosaur footprints come from mudflats along the seashore. If they were incapable of flying off after landing in such areas, he says, they would have quickly died out.
What did pterosaurs eat? Because pterosaur fossils and footprints have been found primarily in marine and freshwater environments, paleontologists believe many pterosaurs had tastes similar to modern sea- and shorebirds. For example, the ancient salt lakes in southwestern Texas in which Quetzalcoatlus was found contained lots of crustacean burrows but no bones from larger animals like crocodiles that might have fed a carrion eater. Some pterosaurs had beaks shaped like those of spoonbills. Pterodaustro had a mouthful of strainer-like teeth that it probably used to filter microscopic plankton from the water. Pteranodon is thought to have scooped up its prey and stashed it in a pelican-like throat pouch.