Scientists have discovered that giant toothless pterosaurs ruled the skies over 60 million years ago.

With wingspans that reached around 39 feet, scientists dubbed the flying creatures "dragons" and deem their discovery a vital piece in exploring the evolutionary transitions that occurred between the prehistoric era and modern times.

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These creatures were said to have lived in different environments around the world, but were particularly drawn to large bodies of water, particularly lakes and rivers, the scientists noted in a study published August 11 in the journal "ZooKeys."

Like modern birds, pterosaurs, part of the Azhdarchidae family, had no teeth.

Paleontologists believe the toothed ancestors of these winged creatures died off due to high levels of carbon dioxide or greenhouse gas, which consequently caused tiny marine animals to die. The death of these creatures then led to a mass extinction 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," the study's author, Alexander Averianov said.

Averianov is a professor from the Zoological Institute of the Russian Academy of Sciences.

Data on the prehistoric creature is extremely hard to gather, so information about it is sparse.

Fossils of the pterosaur have been found in soft sediment deposits known as Konservat-Lagerstätten, so the bones have become fragmented, very fragile and hard to find.

Averianov noted in his study that around 35 percent of the fossils were unearthed from marine sediments, 18 percent from lagoons, 17 percent each from river sediments and coastal plains and, 13 percent from lake sediments.

"The few articulated skeletons are poorly preserved, and some of the best available material has remained undescribed for forty years," he said.

Because of the scarcity of information and difficult circumstances, many scientists have over-estimated the number of pterosaur species and have misclassified some of the bones.