Fossilized bird discovered with unlaid egg is a first

Birds have been around and laying eggs for hundreds of millions of years. With all the bird fossils that have been found, none of them have ever had evidence of an egg inside. Paleontologists working in what is now northwest China have made an incredible discovery of a fossilized bird that has an unlaid egg inside.

That unlaid egg inside the bird may be what killed it 115 million years ago. The team says that the bird was on the verge of laying the egg when it dropped dead on the shore of an ancient lake and stayed there as a well-preserved fossil for millions of years. The ancient bird was named Avimaia schweitzerae.

The team thinks that the egg inside the mother bird could shed light on reproductive disorders in ancient birds. If pigments in the shell of the egg are preserved, they could shed light on how ancient birds nested. Past research has proven that the colors and speckles on dinosaur eggshells vary depending on nesting behavior. This holds true with birds in modern times as well.

Along with the preserved egg, the Avimaia fossil is believed to have a preserved medullary bone. That is a special bone found only in reproductively active female birds. The team says that inspection of the fossil showed that some parts of the egg had up to six layers of shell.

In living birds, trauma can cause the female to delay laying her eggs, encasing it in more layers of eggshell. This is called egg binding, and it can suffocate the developing embryo and kill the mother. The team found no embryo in the egg in this case.