The first 3-D preserved eggs of an ancient reptile unearthed in China shed light on the lifestyle and social patterns of pterosaurs, flying reptiles that lived over 100 million years ago during the time of the dinosaurs.

In China's Xinjiang Province, paleontologists discovered five intact fossil eggs - alongside the bones of 40 adults - all belonging to a previously unknown pterosaur species named Hamipterus tianshanensis, with a wingspan between 5 feet (1.5 meters) and 11 feet (3.4 meters).

"This is definitely the most important pterosaur site ever found," paleontologist Zhonghe Zhou told Reuters.

Until now, only four pterosaur eggs had ever been found - three in China and one in Argentina - and all were flattened during the process of fossilization. The Hamipterus eggs were not soft and leathery like those of most reptiles, nor were they hard like a bird's. Instead they had a thin "pliable" shell overlaying a thick membrane, according to the study published in the journal Current Biology.

The site indicates pterosaurs lived in large colonies much like modern birds, in this case, nesting near the lake and burying eggs in moist sand to prevent them from becoming desiccated, fellow researcher and paleontologist Xiaolin Wang said.

"One of the significant (aspects) of this discovery - hundreds of individuals and eggs together from one site - is that it confirmed that pterosaurs were gregarious, and the population size is surprisingly large," Zhou added.

The fossils also illustrated important sex differences in pterosaurs - Earth's first flying vertebrates. For example, males possessed distinctly larger head crests.

According to the study scientists believe the pterosaurs died in a large storm that hit their colony in the Turpan-Hami Basin, south of the Tian Shan Mountains, around 120 million years ago.

"Sites like the one reported here provide further evidence regarding the behaviour and biology of this amazing group of flying reptiles that has no parallel in modern time," paleontologists said.