Pterodactyls weren't just huge flying reptiles — the creatures were as tiny as a small bird, according to a fossil found in China.

The fossil shows the sparrow-sized pterodactyl was toothless, fed on insects, had curved toes and a wing span of just 25 centimetres, making it the smallest known pterosaur discovered, the researchers said in a study published in the Proceedings of the National Academy of Sciences. Pterosaurs were the first vertebrates to develop the ability to fly.

Scientists believe this sparrow-sized pterodactyl, in an artist's rendering, lived in the treetops of northeastern China and fed on insects.
(AP Photo/PNAS/ National Academy of Sciences, Michael Skrepnickaption)

Previously discovered pterosaurs were massive, with wingspans ranging up to 10 metres. Although the newfound fossil was not an adult, some of the bones were fully grown, which indicated to researchers that it was not a hatchling or newborn.

"How much could it grow? We have no idea," Alexander Kellner of the National Museum of the Federal University of Rio de Janeiro told the Associated Press. "But even if it would double its size, it would still be the smallest of its particular group."

The team, which was led by Xiaolin Wang of the Beijing-based Chinese Academy of Sciences, discovered the fossil in China's northeastern Liaoning province and said the creature likely lived in the canopies of forests there about 120 million years ago.

The find was important, they said, because other pterosaur fossils have generally been found in coastal areas. The newly discovered creature, which has been dubbed nemicolopterus crypticus — or hidden flying forest dweller — indicates that pterosaurs also ranged inland, researchers said.

"We just had one side of the story of pterosaur evolution," Kellner said. "This is now providing us with information about pterosaurs that were living deep inside the continent."

Scientists generally agree that although pterosaurs and dinosaurs are related, the two are separate, Kellner said. Pterosaurs are basically dinosaurs that learned how to fly, and which subsequently evolved differently.