Size and Weight:
Almost certainly the largest creature--whether bird, insect, mammal or reptile--ever to take to the air, Quetzalcoatlus did credit to the fearsome Aztec god after which it was named. The most impressive species of this giant pterosaur attained wingspans of over 30 feet, and must have been greatly feared by terrestrial critters when they soared down from the sky in search of food. Right? Well, maybe not: a recent analysis of Quetzalcoatlus' anatomy hints that this pterosaur may have led a completely terrestrial existence, stalking its prey on two legs like the contemporary raptors and tyrannosaurs of the late Cretaceous period. (See 10 Facts About Quetzalcoatlus and a gallery of Quetzalcoatlus pictures.)
The fact is, paleontologists are still trying to piece together exactly how Quetzalcoatlus lived. It's generally agreed that, if this reptile indeed flew, it glided rather than flapped its wings, which given its size and presumed cold-blooded metabolism would likely have been an anatomical impossibility. (A recent study concludes that Quetzalcoatlus needed a long, sloping runway in order to take off; otherwise, this pterosaur preferred to launch itself off the edge of cliffs.) Even less certain is how Quetzaloatlus fed; it may have scavenged already-dead carcasses like a vulture, gobbled down fish like a stork, or plucked out unfortunate fish, plesiosaurs and mosasaurs as it skimmed close to the North American shoreline.
As big as it was, Quetzalcoatlus wasn't the only plus-sized pterosaur of the Mesozoic Era, though it vastly outweighed its nearest relatives. The next biggest pterosaur on the block was probably Ornithocheirus, and a pair of genera from South America, Tapejara and Tupuxuara, also cut impressive profiles (and were probably brightly colored as well; we know virtually nothing about how Quetzalcoatlus might have looked at the height of the mating season). By the way, some paleontologists think the European pterosaur Hatzegopteryx may have been even bigger than Quetzalcoatlus, but limited fossil remains make speculation difficult.