About 110 million years ago, a sparrow-sized bird died with her egg still inside her body. That egg, crushed and flattened by pressure over time, is the first unlaid bird egg known to be preserved in a fossil, researchers report March 20 in Nature Communications.
The fossil was unearthed 11 years ago in northwestern China. In 2018, paleontologists led by Alida Bailleul of the Key Laboratory of Vertebrate Evolution and Human Origins in Beijing took a closer look, and noticed something odd: The bird had a strange sheet of tissue between her pubic bones. Examining a piece of the tissue under a microscope, Bailleul found that it was from an egg.