Ancient dinosaur egg fossil found in Yunnan sheds light on eggshell evolution

Chinese scientists have identified a new type of dinosaur egg fossil in Yunnan province that dates back about 195 million years and sheds new light on how dinosaur eggshells evolved from soft membranes into more rigid, mineralized structures.

The fossil was discovered in 2008 in the Lufeng Formation in Lufeng, Chuxiong Yi autonomous prefecture, encased in a rock slightly smaller than a chicken egg. Named Mutabilisoolithus dawaensis, it is among the oldest and best-preserved dinosaur eggshells known worldwide, according to a study published in the journal Nature Communications on Oct 26.

The research was conducted by a team from Hebei University and the dinosaur fossil conservation and research center of Lufeng's natural resources bureau, among other institutions.

Using chemical analysis and advanced imaging, including micro-CT scanning, researchers determined that the eggshell belonged to an early sauropodomorph dinosaur from the Early Jurassic period.

Unlike the hard shells of modern bird eggs, the ancient eggshell had an unusually thick membrane and a very thin layer of calcium-based minerals, suggesting it remained soft and flexible despite having begun to develop a mineralized outer layer.

Researchers believe this unusual structure may represent one of the earliest stages of eggshell mineralization, helping bridge an evolutionary gap between soft eggs with no mineralized shell and those with a tougher, partially mineralized covering.