Ancient winged reptiles called pterosaurs were so successful they ruled earth's skies for tens of millions of years, according to a study published in the journal ZooKeys.

The fearsome flyers, part of a family of pterosaurs named Azhdarchidae, get their name from azdarha, the Persian word for "dragon".

This artist's rendition from a study in PLOS One in 2008 shows a group of giant azhdarchids, Quetzalcoatlus northropi, foraging on a Cretaceous fern prairie. A new paper in ZooKeys says toothless pterosaurs were once found around the globe. Credit:Mark P Witton and Darren Naish

Unlike earlier pterosaurs, they had no teeth, and they dominated from late in the Cretaceous period (about 90 million years ago) until the extinction event that also killed off the dinosaurs about 66 million years ago.

"This shift in dominance from toothed to toothless pterodactyloids apparently reflects some fundamental changes in Cretaceous ecosystems, which we still poorly understand," study author Alexander Averianov of the Russian Academy of Sciences wrote in the paper.