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The fossils of Hamipterus tianshanensis(Wang et al. in Curr Biol 24:1323–1330, 2014) and their eggs have important scientific significance because they can provide unique information about the reproduction, development, and evolution of pterosaurs. The fossils and the rock surrounding them have, however, been weathered, which including powdering and flaking, since they were relocated from Xinjiang to Beijing. The high content of soluble salts is a significant factor in fossil deterioration because the dissolution–recrystallization process can generate tremendous pressure and lead to decreased mechanical strength. This study evaluated the electrokinetic desalination performance for the fossils, and two types of poultices employed including paper pulp from Bioline®and CKS121 (cellulose: kaolin: sand = 1:2:1, w/w). Mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), ion chromatography (IC), and other methods were applied to evaluate the desalination effect. The surface salt content reduction by applied direct current (DC) was about 70%, and the inner salt content reduction was about 80%. The experimental results suggest that the electrokinetic method is a promising way to desalinate fossils. Nonetheless, cracks appeared in the surrounding rock crack after electrokinetic desalination, which can be explained by the montmorillonite swelling-induced stresses. Pre-consolidation, especially for electro-chemical method may solve the cracking problem for the clay-rich sandstone desalination.

Pterosaur eggs can offer information about pterosaur reproductive strategies and are extremely precious because only a small number of specimens have been discovered. Previous studies have mainly focused on morphological descriptions of pterosaur eggs and their embryos while the chemical composition of pterosaur eggs has received little attention. The conventional view believed that the eggshell was composed of calcite. However, previous SEM–EDS results for Hamipterus tianshanensisshowed that the eggshell contains phosphorus. Therefore, the object of this research is to determine the mineral composition of the eggshell of H. tianshanensis. Two eggs were analyzed by scanning electron microscopy coupled with energy dispersive X-ray spectrometry (SEM–EDS) and Raman spectroscopy. The SEM–EDS results show that both surface and cross section are porous and characterized by small irregularly shaped particulates. Moreover, the distribution of Ca and P has a strict coincidence in the cross-section of eggshells. Furthermore, neither the intense peaks of calcite nor organic peaks can be observed by Raman spectroscopy in eggshells. Meanwhile, the Raman spectroscopy mapping analysis result shows a sharp and intense peak at approximately 966 cm−1among the white eggshell, which can be hard evidence that H. tianshanensiseggs are mainly composed of calcium phosphate. Combined with the present of F in the eggshell, it can be inferred that fluorapatite Ca5(PO4)3F is the main mineral. The fluorapatite eggshell can be interpreted in two ways. One explanation is that H. tianshanensislaid apatite-shelled eggs, similar to living Salvator merianae, and the bioapatite transformed to fluorapatite over geological time. Another possible explanation is that the fluorapatite comes from the result of phosphatization of soft egg membrane tissues through taphonomic processes, indicating that H. tianshanensismight have laid soft eggs. Regardless, the results show that fluorapatite, rather than calcite is the main preserved mineral composition of H. tianshanensiseggshell, correcting the previous view. This study contributes to the present understanding of the mineral composition of pterosaur eggshells and may offer some insight into the pterosaur reproduction pattern.