In northwestern China scientists have found a haul of big number eggs by pterosaurs, the winged reptiles that dwelled close by the dinosaurs. Among them were discovered the most preserved pterosaur embryos.
In spite of the fact that researchers have examined pterosaurs for over two centuries, no eggs were found until the beginning of the 2000s. The new cache, found by Chinese Academy of Sciences scientist Xiaolin Wang, has about 215—300—strikingly kept pterosaur eggs.
THE PERFECT STORMS
The recently discovered eggs are from Hamipterus tianshanensis, a formerly known type of pterosaur that inhabited northwestern China more than a hundred million years ago. Their wingspan reached up to 3 meters and they probably ate fish. These creatures may have looked like the present herons, living close to waters that ran though the inland.
The paper coauthor Shunxing Jiang of the Chinese Academy of Sciences explains that the site where they found them is in the Gobi desert, but in the time when Hamipterus lived, the place was different, in a way like a Pterosaur paradise.
Living in this paradise, Hamipterus probably reproduced there by covering clusters of eggs in plants or on the coast. There is a hypothesis that storms have flooded a nesting site which could be seen from the fossilization of the eggs. But probably these storms took place couple of times, because the eggs are found in four sediment layers.
According to Wang’s team, an old nesting site may have been flooded frequently. This would mean that, similar to living birds and turtles, Hamipterus nested in the same site again and again. Likewise, it can be concluded from the sheer number of eggs that Hamipterus reproduced in big flocks like some modern birds.
LEAVING THE NEST
Lot of the pterosaur eggs broke from the waters of the floods and the sedimentation is the reason why they are so well-preserved. Sixteen of these eggs contain pterosaur embryos, as well as one bone that the scientists believe belonged to a hatchling.
The bones help us to see the characteristics of an embryo, hatchling, and a young specimen when it is developed, stated coauthor Juliana Sayão, a bone-structure specialist at the Federal University of Rio de Janeiro.
The comparison of separate bones from pterosaurs of various ages could explain the development of Hamipterus. The older embryos didn’t have teeth yet developed, and their back extremities were more developed than the front ones. This was unexpected, since lot of scientists believed that pterosaurs were fliers from their hatching. But the Hampiterus fossils, suggest a slower-developing pterosaur that walked on all fours as a baby.
Additional studies should help explain how these winged creatures bred. The shells look like modern turtles’ leathery eggs, which implies that Hamipterus likely hid its eggs in earth—however it is not familiar where or how. In addition, we still don’t know the number of eggs one female Hamipterus laid or how many of them were in the breading groups.
Because the fossil record is insufficient, it’s likely that the suggested Hamipterus development should be modified. Maybe the biggest embryos that were found in China weren’t exactly prepared to hatch, which would divert from the growth sequence. It would be better if more fossils are found, and Wang’s group stays to search for more in northwestern China.