The record of dinosaur eggs from the Upper Cretaceous Wangshi Group in eastern Shandong Province,China shows that the dinosaur species represented by elongatoolithids were present from the middle to the late Late Cretaceous,whereas those represented by the dictyoolithids and spheroolithids became extinct in the middle Late Cretaceous and the new species represented by ovaloolithids appeared in the late Late Cretaceous.Estimated eggshell conductance of water vapor is over 4 to over 115 times higher in spheroolithids and the dictyoolithids than in elongatoolithids and ovaloolithids,indicating that eggs of the first two oofamilies required higher humidity during incubation.Based on the18O record as preserved in eggshell,a change from relatively humid to relatively dry climatic conditions can be assumed to have taken place during the transition between the middle and late parts of the Late Cretaceous.It is reasonable to suggest that the change in climate was the cause of the dinosaur diversity.
