Gigantic toothless beings, called pterosaurs, dominated the skies in the late Cretaceous period some 60 million years ago and could be found all over the planet, a new study said. According to scientists, these ancient creatures that resembled storybook dragons, played a significant role in the ecosystem of the time.

The toothless pterosaurs from the Azhdarchidae family are considered to be some of the largest known flying beings of all times, with wing spans stretching 39 feet across. These "dragons," which replaced their toothed predecessors, were the last of their kind to inhabit the planet, according to the study, published in the journal ZooKeys. The name Azhdarchidae comes from the Persian word “aždarha,” which means dragon.

“This shift in dominance from toothed to toothless pterodactyloids apparently reflects some fundamental changes in Cretaceous ecosystems, which we still poorly understand,” Alexander Averianov of the Zoological Institute of the Russian Academy of Sciences, and the study’s author, said in a statement.

The pterosaurs, which are believed to be the first airborne vertebrates, likely inhabited a large variety of environments, but were particularly abundant near large lakes, rivers and coastal environments.

As part of the study, Averianov examined 54 known Azhdarchidae fossils, including 51 bones and three fossilized tracks, Christian Science Monitor reported.

According to scientists, pterosaur bones are more fragile than other dinosaur bones, and are confined mostly to soft sediment deposits called Konservat-Lagerstätten. The Azhdarchidae evolved mostly during the Late Cretaceous period, however, fossils from this period are extremely rare, making it hard for paleontologists to study these giant prehistoric creatures.

“Azhdarchidae currently represent a real nightmare for paleontologists… the few articulated skeletons are poorly preserved, and some of the best available material has remained undescribed for forty years,” Averianov said.