Pterosaur eggshell structure and its implications for
pterosaur reproductive biology
By
David M. Unwin1* & D. Charles Deeming2
1Department of Museum Studies, University of Leicester, 103-105 Princess Road
East, Leicester, LE1 7LG, UK.
2Department of Biological Sciences, University of Lincoln, Riseholme Park,
Lincoln, LN2 3LP, UK

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.