The largest creatures that ever flew may have spent much of their time on the ground, research suggests. Azhdarchids were a type of pterosaur, or "winged lizard", living at the time of the dinosaurs. Their wingspans could exceed 10 metres (32ft). They were thought to have lived like seagulls or pelicans, patrolling coastlines from the air and swooping down on fish in the water. But new evidence from their fossil distribution and footprints suggests they were more likely to stalk prey on foot.
Darren Naish, from the University of Portsmouth, and his team studied fossils in London, Portsmouth and Germany, and compared the physical characteristics of azhdarchids with those of modern animals.
Azhdarchids have puzzled scientists since the 1970s. Originally described as vulture-like scavengers, they were later thought to have used their long pointed beaks to probe for prey in mud. Most experts assume they flew over the surface of coastal waters like modern seabirds, searching for fish. But Naish, writing in the journal PLoS ONE, disagrees.
The huge flying reptiles, which lived between 65m and 230m years ago, are named after the Uzbek word for "dragon". They had long toothless bills, and when standing on the ground could be as tall as a giraffe. In flight they could be as large as a modern light aircraft.
Naish believes the azhdarchids were more like ground-feeding hornbills or storks than pelicans.
"All the details of their anatomy, and the environment their fossils are found in, show that they made their living by walking around, reaching down to grab and pick up animals and other prey," he writes. The team looked at the azhdarchid neck, which was unusually stiff. They found it fitted in well with the "terrestrial stalker" theory, since all a grounded azhdarchid had to do was raise and lower its bill tip. The creatures' small padded feet and long but weak jaws also suggested a ground-living lifestyle.
His co-researcher, Mark Witton, said: "The small feet of azhdarchids were no good for wading around lake margins or swimming should they land on water, but are excellent for strutting around on land. As for what azhdarchids would eat, they'd have snapped up bite-size animals or even bits of fruit. But if your skull is over two metres in length then bite-size includes everything up to a dinosaur the size of a fox."
More than half the known azhdarchid fossils were recovered from sediments that were laid down inland, the researchers found.