Dec. 1, 2004 — Two new discoveries of pterosaur eggs from China and Argentina are showing that the flying reptiles of the dinosaur age were likely more diverse than their modern bird counterparts.

In Argentina, the discovery of a fossilized hard-shelled egg of a flamingo-like pterosaur is firming up the case for the site of discovery once being a pterosaur rookery.

In China, the first-ever pterosaur egg discovery announced earlier this year has been followed with the discovery of a second egg that appears to have had a tough leathery shell, like those of some modern reptiles.

Both discoveries are reported in this week's issue of the journal Nature.

"This is just a very exciting time for people working on flying reptiles," said pterosaur researcher Luis Chiappe of the Natural History Museum of Los Angeles.

Chiappe and his colleagues have been unearthing hundreds of pterosaurs at an unusual site called Loma del Pterodaustro in central Argentina.

The fossils include adults, hatchlings and now an embryo inside an egg. The predominance of pterosaurs of all ages at Loma del Pterodaustro is strong evidence that 100 million years ago the place was similar to many bird rookeries today: located in a harsh, hard-to-reach place that provided safety for the younger birds, Chiappe said. That, in turn, suggests the existence of some kind of parental care, he said.

The Argentine pterosaurs were probably living a lot like some flamingoes do today — in large flocks beside what was likely an extra salty lake, in which they used their specially adapted beaks to filter food, said Chiappe.

The 121-million-year-old Chinese pterosaur egg, on the other hand, says less about lifestyle and more about how very different pterosaurs were from each other.

"Our observations indicate that this pterosaur egg from Yixian had a soft, leathery shell, similar to those widely found among ... crocodiles and turtles," reported the Chinese team from Nanjing University, The Chinese Academy of Geological Sciences, Taiwan's National Museum of Natural Sciences and the University of Geosciences in Beijing.

Such a difference in something as basic as the shells of pterosaurs highlights what a large and diverse group of animals they were, more diverse than today's birds, said pterosaur researcher Sankar Chatterjee, curator at the Museum of Texas Tech University.

"You have to remember that pterosaurs are a group that lived for 160 million years," said Chatterjee.

With that much time to evolve and such obvious differences, it's more that likely today's birds are just reinventing lifestyles that pterosaurs had long ago, he said.