Well-preserved eggs laid by a pterosaur - ancient flying reptiles that grew to the size of small aircraft - have been discovered for the first time, shedding new light on the mysterious creatures.
The hugely significant find in China suggests at least some of the creatures lived in large nesting colonies, much like modern birds.
Five three-dimensionally intact fossil eggs were found at the site in Xinjiang province, north west China, along with the bones of around 40 male and female adults.
All belonged to a previously unknown pterosaur species, Hamipterus tianshanensis, which had a wingspan of between 1.5m and 3.4m.
Scientists believe the thin-shelled eggs, showing signs of cracking and crazing, were not part of the same clutch.
Writing in the journal Current Biology, the researchers led by Dr Xiaolin Wang, from the Chinese Academy of Sciences in Beijing, said: "The combination of many pterosaurs and eggs indicates the presence of a nesting site nearby and suggests that this species developed gregarious behaviour.
"Hamipterus likely made its nesting grounds on the shores of freshwater lakes or rivers and buried its eggs in sand along the shore, preventing them from being desiccated."
Previously the only pterosaur eggs known to science were four poorly preserved and flattened specimens, three from China and one from Argentina.
The Hamipterus eggs were not soft and leathery, such as those of most reptiles, nor were they hard like a bird's.
Instead they had a thin pliable shell overlaying a thick membrane.
The modern rat snake lays a similar type of egg, said the scientists.
"We regard the eggshell structure found in Hamipterus as a general trend for pterosaurs," they added.
The pterosaurs are thought to have 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.
Adult bones recovered included male and female skulls as well as vertebrae and limbs.
Both sexes sported head crests that were different in size and shape, those of males being larger.
"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," the researchers concluded.
Pterosaurs are often confused with dinosaurs but belonged to a distinct reptilian group. Much less is known about them than the dinosaurs.
They were the first vertebrates known to have evolved powered flight and showed enormous diversity.
Species ranged from creatures the size of a sparrow to the monstrous Quetzalcoatlusa, which had a wingspan of 12m.
Towards the end of their time on Earth, only the larger species remained, as the smaller ones were out-competed by early birds.