Unlaid egg discovered in ancient bird fossil
Unlaid egg discovered in ancient bird fossil
belonging to a sparrow-size flyer that lived in northwestern China 110 million years ago—is
especially remarkable because fully formed eggs typically only stay within an adult bird for about
24 hours.
Researchers were initially puzzled by the discovery, as they never suspected the unusual,
squashed mass within the headless fossil’s abdomen (seen as a flattened brown layer in the
center of the picture) could be an egg. But a microscopic analysis of a fragment revealed it to be
eggshell. Further study suggested structural abnormalities that hint that the egg may have been
the cause of this bird’s demise, the paleontologists report today in Nature Communications.
The fossil eggshell’s structure doesn’t have the correct proportions seen in healthy eggs and
consists of multiple layers of shell. This indicates a condition called “egg-binding,” where an egg
becomes trapped inside a bird, the team argues. This can occur in chickens and small varieties
of modern pet birds under stress and likely also led to the death of this long-lost, dinosaur-era
relative.
This makes the discovery “the oldest documented case of this common reproductive disorder,”
the researchers say. Intriguingly, the eggshell features microscopic spheres of calcium
phosphate, which is seen today in birds that nest in humid, infection-prone environments. This
waterproofing suggests it was a species that nested near water and buried its eggs in the
ground.
The team has christened the bird Avimaia schweitzerae. (Avimaia means “mother bird”; and
schweitzerae honors paleontologist Mary Schweitzer.)
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