Walking tall

Some pterosaurs were well adapted to life on the ground

May 27, 2008 at 7:26 pm

Some types of the largest flying reptiles ever known, including a species that had an estimated 12-meter wingspan, were well adapted to life on the ground as well, a new analysis suggests.

FLYING GIANT The largest flying reptile, an azhdarchid pterosaur called Hatzegopteryx thambema, had giraffelike proportions and a 12-meter wingspan. Witton

AFTERNOON SNACK A new study suggests that some pterosaurs (illustrated here) could not only fly but also walk. They likely foraged in open forests or on fern prairies and ate hatchling dinosaurs and other small prey. Witton

Most fossils of pterosaurs, flying reptiles that soared ancient skies while the dinosaurs strolled below, have been found in marine sediments. That fact, among others, had led many paleontologists to propose that the creatures spent much of their time flying over the seas, possibly even feeding by snatching fish from the water, says Mark Witton, a vertebrate paleontologist at the University of Portsmouth in England. However, an analysis of fossils by Witton and his colleague Darren Naish cast doubt on that lifestyle hypothesis for the largest pterosaurs, a group of species called azhdarchids.

First, most azhdarchid fossils are found in sediments deposited on land, such as those laid down in lakes or floodplains. For example, those of Quetzalcoatlus northropi, an azhdarchid with a 10-meter wingspan, were fossilized at a locale in what is now Texas more than 400 kilometers from what would have been the nearest coastline of its era, says Witton. Moreover, most of the azhdarchid fossils found in marine sediments are fragmentary, a sign that the bones may have been transported a long way by rivers before reaching their final resting places.

Second, many of the creatures’ anatomical features also hint at land-based lifestyles. Their feet are small and relatively slim, a sign that these flying reptiles probably weren’t good waders or swimmers. The few sets of footprints attributed to azhdarchids suggest that the creatures walked upright and with their limbs beneath them, not sprawled like alligators and some other reptiles.

Finally, the typical azhdarchid’s neck wasn’t flexible, and its lower jaw didn’t have strong muscles, requirements for grabbing food from the sea while on the wing. Also, the shape of the creatures’ bills doesn’t match those of modern-day birds that probe in mud or sand for their meals.

Together, the evidence suggests that azhdarchids were well adapted to life on land. The creatures, the largest of which had giraffelike proportions, probably foraged through open woodlands or fern prairies, snatching up young dinosaurs and other unfortunate prey, says Witton. “Analyses suggest that azhdarchids were quite capable on the ground.”