What was as tall as a giraffe, weighed a scant 550 pounds, and could fly? This is not a trick question. Around 68 million years ago, such creatures tromped and flew over what is now Texas. Paleontologists know this animal as Quetzalcoatlus northropi – a fantastically huge pterosaur that belonged to a group called azhdarchids. The biggest members of this leathery-winged lineage were the largest creatures ever to fly over our planet, and the increasing amount of information paleontologists have gleaned from their bones has repeatedly underscored a persistent riddle. How did these unusual flyers get to be so enormous?

Superlative size sparks our imagination and demands explanation. We’re constantly drawn to mysteries such as why