Giant toothless reptiles with wingspans that stretch 39 feet across dominated the ancient skies 60 million years ago and these creatures were so successful that they ruled the skies for millions of years, findings of a new research have found.

The study which was published in the journal ZooKeys on Aug. 11 suggests that the flying creatures named Azhdarchidae which belongs to the family of pterosaurs, were found globally and likely had crucial role in the ecosystem of the Late Cretaceous period.

Fossil records show that pterosaurs were probably the first airborne vertebrates that flew in the skies. A research presented at the 2012 Geological Society of America meeting also showed that some pterosaurs were so big that they needed to run to take off and had a difficult time landing.

Despite their gigantic size, the Azhdarchidae, which took their name after "azdarha," a Persian word that means "dragon," had no teeth unlike earlier pterosaurs. It is believed that this group of toothless reptiles became the dominant species replacing their toothed relatives after high levels of carbon dioxide caused the death of microscopic marine organisms that eventually led to a mass extinction approximately 90 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," said Alexander Averianov, from the Zoological Institute of the Russian Academy of Sciences in Saint Petersburg, Russia, who conducted the study.

The ancient animals were neither dinosaurs nor ancients birds but studying pterosaurs could provide insights on how ancient ecosystems worked. It could also give clues as to the origins of flight as these large predators are believed to be the first animals after insects that developed the capability for powered flight.

Because these animals also have fragile bones, pterosaur fossils can be hard to find. Their bones do not survive as well as the remains of the dinosaurs resulting in largely incomplete fossil records and posing challenges for researchers studying these creatures.

The study, however, pointed out that while the bones of these reptiles are difficult to find, they were likely successful in a number of different habitats. They were also commonly found in lakes, rivers and particularly in near-shore marine environments.

"Azhdarchids likely inhabited a variety of environments, but were abundant near large lakes and rivers and most common in nearshore marine paleoenvironments," Averianov wrote.