Wednesday, May 28, 2008

Giant Flying Reptiles Preferred To Walk

A Reappraisal of Azhdarchid Pterosaur Functional Morphology and Paleoecology. 2008. Witton MP and Naish D. PLoS ONE 3(5): e2271.

Life restoration of a group of giant azhdarchids, Quetzalcoatlus northropi, foraging on a Cretaceous fern prairie.
New research into gigantic flying reptiles has found that they weren’t all gull-like predators grabbing fish from the water but that some were strongly adapted for life on the ground.
A new study on one particular type of pterosaur, the azhdarchids, claims they were more likely to stalk animals on foot than to fly. Azhdarchids were probably better than any other ptersosaurs at walking because they had long limbs and skulls well suited for picking up small animals and other food from the ground.

Azhdarchids, named after the Uzbek word for 'dragon', were gigantic toothless pterosaurs. Azhdarchids include the largest of all pterosaurs: some had wingspans exceeding 10 metres and the biggest ones were as tall as a giraffe.

The probable azhdarchid trace fossil Haenamichnus uhangriensis.

Dr Naish said: “Azhdarchids first became reasonably well known in the 1970s but how they lived has been the subject of much debate. Originally described as vulture-like scavengers, they were later suggested to be mud-probers (sticking their long bills into the ground in search of prey), and later still suggested to make a living by flying over the water’s surface, grabbing fish.

Animals like azhdarchids no longer exist but the closest analogues in the modern world are large ground-feeding birds like ground-hornbills and storks.

“We worked out the range of motion possible in the azhdarchid neck: this bizarrely stiff neck has previously been a problem for other ideas about azhdarchid lifestyle, but it fits with our model as all a terrestrial stalker needs to do its raise and lower its bill tip to the ground.”

Reconstructed skeleton of Zhejiangopterus linhaiensis. Scale bar = 500 mm.
Other aspects of azhdarchid anatomy, such as their relatively small padded feet and long but weak jaws often pose problems in other proposed lifestyles but fit perfectly with the terrestrial stalker hypothesis. Mr 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.” LINK