The baby dinosaur seemed almost ready to burst free from its shell, curled up so tightly its head tucked between its toes. But an unknown event buried the egg before the small creature ever took its first breath, preserving the unhatched animal for tens of millions of years in what is now southern China.

The stone mining company Yingliang Group discovered the egg in 2000, but another 15 years passed before anyone realized the significance of the find, when a few fragile bones exposed by a crack in the egg's surface hinted at the prize inside.

As scientists report this week in the journal iScience, nestled under the fossil egg's dimpled surface is one of the most