Fig. 1

Pterosaur fossil bones encased in sandstone matrix, and their mineral composition. A Pterosaur fossil and fossil-surrounding rocks. The fossils are embedded in sandstone with brown boulder clay. The hollow pterosaur bone fossil is thin and fragile. When the surrounding rock is pulverized and exfoliated, the fossil begins to crack and exfoliate because of a loss of mechanical support. B the weathered fossil. The specimens were collected in the field and was put into the sample bag. When the fossil transported indoors, the surrounding rock was powdery and some bones were broken. C The mineral composition of mudstone breccias (wt%). D The mineral composition of sandstone (wt%). Pie charts (C–D) are based on the XRD results from Li et al. [7]