Abstract

The recent discovery of pterosaur eggs containing embryos has provided important evidence regarding the structure of pterosaur eggshell. Two eggs, from the same locality and horizon in China, have a shell that appears to have been parchment-like and pliable with no detectable mineralised calcareous component. A third egg, from Argentina, preserves evidence of a single layer of calcite. This is only 30 microns in thickness, however, and thus very much thinner than mineralised layers reported in turtles that lay pliable-shelled eggs. All three examples resemble the parchment-shelled eggs of squamate reptiles, but exhibit variation in the degree of calcification of the outer surface, which also varies between squamate species. It seems unlikely that the parchment-shelled eggs of pterosaurs were incubated by direct contact with the body of a parent because of the risk of crushing the egg. Moreover, the likely high permeability of a parchment-like eggshell would have required burial in a very humid environment, such as sand, soil, or perhaps in mounds of rotting vegetation, to prevent desiccation during incubation. Consequently, pterosaur eggs are likely to have developed in a thermal environment close to ambient temperatures and probably subject to some temperature variation.