Over 120 million years ago, on the banks of a lake in what is now modern-day China, you would have been greeted by a chattering, rowdy scene as a colony of pterosaurs nested in the sand. Soon after, however, a sandstorm pelted the nesting site and buried hundreds of the eggs in perfect condition, even preserving the first known three-dimensional pterosaur embryo.
Up until now, only a handful of pterosaur eggs preserved in three dimensions were known to science, with three unearthed in Argentina and five from China. This new find blows all the others out of the water, as paleontologists have painstakingly uncovered an astonishing 215 eggs all frozen in time. Even more incredible, 16 of these still contain the developing embryos of the tiny pterosaurs inside. The team's results have been published in Science Advances.
In general, bone beds containing such a rich array of pterosaur fossils are extremely rare. This limits our understanding of the ancient animal’s behavior, including how they were organized socially and how they developed.
All the pterosaur remains found in this prehistoric burial ground belong to a single species called Hamipterus tianshanensis, which was actually only recently described by the same team a few years ago. The discovery shows that the species likely gathered in single, large colonies, since the remains of no other species of pterosaur have been recovered from the site.
Despite the massive number of eggs found in a single mass, the researchers concluded that it likely represents the offspring of multiple females, rather than just one hugely prolific individual. This is supported by the fact that the eggs vary in size, suggesting either a difference in the age of the clutches or that some females laid larger eggs, which can happen even in modern reptiles. While this confirms colonial nesting of the pterosaurs, the team are unable to ascertain a typical clutch size.
Before the preservation event, the animals were likely nesting on the sandy bank of a lakeshore, possibly burying their soft-shelled eggs in the sand. When a particularly strong sandstorm blew through, the nests were probably blown out into the lake, where they floated before sinking into the sediment at the bottom, where they remained for 120 million years.
The embryo remains show that the animals grew relatively slowly. While their legs were well developed, their wings were not. This suggests that once they hatched, the newborns were unable to fly and their parents would have cared for them.
This incredible find has expanded our knowledge of pterosaurs, and suggests that large colonies of the animals were likely a common sight during the Early Cretaceous.