Scientists studying fossil remains in eastern China have uncovered a rare and puzzling discovery: two nearly spherical dinosaur eggs that contain no traces of embryos or bones, but are instead filled with large mineral crystals. The finding offers fresh insight into how fossilisation can occur under unusual geological conditions and sheds light on the environment during the final years of the dinosaurs.
The eggs were discovered in the Qianshan Basin of Anhui Province, an area known for preserving Late Cretaceous fossils. Measuring about 13 centimetres in diameter, the eggs were remarkably well preserved on the outside. However, when researchers examined their interiors, they found hollow chambers lined with clusters of calcite crystals rather than organic remains.
According to the research team led by Qing He of Anhui University and the Nanjing Institute of Geology and Palaeontology, the eggs likely lost their organic contents early after burial. Groundwater rich in dissolved minerals then seeped into the empty shells, allowing calcite to crystallise slowly over millions of years. This rare mineral replacement preserved the internal structure of the eggs in an unexpected way.
The eggs have been classified as a new oospecies named Shixingoolithus qianshanensis and placed within the Stalicoolithidae family, which is characterised by thick-shelled, spherical eggs. Because no skeletal remains were found, the classification was made using parataxonomy, a method that allows scientists to categorise fossil eggs based on shell structure rather than the species that laid them.
Microscopic analysis of the eggshells revealed patterns consistent with other stalicoolithid eggs, confirming the classification. Researchers noted that such crystal-filled eggs are extremely rare and demonstrate how fossilisation can vary widely depending on environmental and chemical conditions.
In contrast to the Anhui discovery, another recent find in southern China revealed a more familiar form of preservation. In the Ganzhou Basin of Jiangxi Province, scientists uncovered dinosaur eggs containing well-preserved hadrosauroid embryos. These fossils were found during construction work and later analysed in a peer-reviewed study published in BMC Ecology and Evolution.
The embryos displayed developing vertebrae, skull bones, and limb structures, indicating early growth stages. Their features suggest they belonged to a less advanced group of hadrosauroids, distinct from larger duck-billed dinosaurs known from later periods. The eggs themselves were relatively small, supporting the idea that egg size and hatchling development evolved over time within the group.
Both discoveries date to the Maastrichtian stage of the Late Cretaceous period, just a few million years before the mass extinction that wiped out non-avian dinosaurs. During this time, regions of present-day China experienced volcanic activity, flooding, and climate fluctuations that contributed to rapid burial and exceptional fossil preservation.
Scientists say these findings do not directly explain the cause of dinosaur extinction, but they help reconstruct ecosystems at the very end of the Mesozoic Era. By studying differences in eggshell structure, mineral composition, and embryonic development, researchers can better understand how dinosaurs reproduced and adapted in a changing world shortly before their disappearance.
The crystal-filled eggs from Anhui stand as a reminder that fossil records can still surprise scientists, revealing not just remnants of ancient life, but also the powerful geological processes that shaped what survived into the present.