Scientists have discovered the first intact eggs from pterosaurs, the flying reptiles that lived alongside the dinosaurs. The eggs, along with dozens of pterosaur fossils, are from a site discovered in 2005 in northwestern China. In a new study in the journal Current Biology, the scientists report that the pterosaurs belong to a new genus and species, Hamipterus tianshanensis, dating to the Early Cretaceous, 145 million to 100 million years ago. They had wingspans of five to 11 feet.

About 40 fossils, both male and female, were recovered from the site, said the study’s senior author, Alexander W. A. Kellner, a paleontologist at the Federal University of Rio de Janeiro.

“This is the best evidence showing that at least this new pterosaur species was gregarious, meaning that several lived together, perhaps nested together,” he said.

The researchers, from Brazil and China, used spectroscopy and electron microscopy to scan the eggs and discovered they had a hard external layer enclosing a soft, thick internal membrane, much like snake eggs.