But enough is preserved to allow comparisons between the bones in the embryos and those of older pterosaurs also preserved, says Alexander Kellner of the National Museum at the Federal University of Rio de Janeiro in Brazil, who helped analyze the fossils. The newly discovered trove, belonging to a species called Hamipterus tianshanensis that lived around 120 million years ago, offers clues into the development and anatomy of freshly hatched pterosaurs.
The eggs date to the Lower Cretaceous period, between 145 million and 100 million years ago. "What really impresses me is that it captures nearly an entire life history: eggs, hatchlings, juveniles, sub-adults and adults".
Wang said up to 300 eggs may be present at the excavation site near the city of Hami because more appear to be buried under the exposed ones. Pterosaurs had thin bones, one of the traits contributing to their flying capacity, so finding remains is challenging, not to mention eggs-only six three-dimensional preserved eggs from China and Argentina had been found earlier, according to the study.
"All are deformed to a certain extent, which indicate their pliable nature", said the study.
"Although most eggs are complete, small fissures resulting from decomposition and compression during burial must have occurred because all eggs are filled with sandstone, which ultimately accounts for their three-dimensionality".
"Lastly, the fact that a single collection of embryos exhibits a range of developmental stages hints that pterosaurs participated in colonial nesting behavior".
Scientists said Thursday that they had unearthed 215 eggs of the fish-eating Hamipterus tianshanensis - a species whose adults had a crest atop an elongated skull, pointy teeth and a wingspan of more than 11 feet (3.5 meters) - including 16 eggs containing partial embryonic remains. For example, newborns were likely not being able to fly yet, because of the lack of a wing muscle-related element in some observed embryos. "They needed some sort of parental care", Kellner says.
"Based on growth marks, we estimate one of the individuals to be at least 2 years old and still growing at the time of its death, supporting the growing body of evidence that pterosaurs had long incubation periods".
There had been a paucity of pterosaur eggs and embryos in the paleontological record because it is hard for soft-shelled eggs to fossilize.
Other experts say that the find will be significant for understanding pterosaur reproduction.
"Wang et al.'s study is remarkable for the number of eggs in association with adults and juvenile pterosaurs that it reports on", Deeming said.