In 2021, scientists found an unborn dinosaur frozen inside a museum egg for 70 million years, and the fossil revealed its final moments before hatch day

Most great scientific discoveries happen in dramatic places: dusty canyon floors, remote mountain ranges, deep underwater. This one started in a storeroom.

In 2000, a fossil egg was quietly acquired from southern China as a possible dinosaur specimen. For years, it remained largely unexamined. Then, in 2021, while renovating the Yingliang Stone Natural History Museum, staff saw something amazing: little bones poking out of a crack in the shell. The scientific community was stunned by what the scientists discovered when they carefully prepared the fossil.

That egg contained one of the most complete dinosaur embryos ever discovered: a curled, 27-centimeter skeleton that had been preserved for some 70 million years. They called it Baby Yingliang.


A pose that should not exist
The embryo’s head is beneath its body, its feet on either side, and its back curled along the blunt end of the egg, a posture never seen before in a non-avian dinosaur but which looks remarkably like that of a late-stage modern bird embryo.

If you've ever seen a baby chick about to hatch, you know this pose. Birds instinctively curl up into a compact position, “tucking” so they orient themselves to break out of the shell. In modern birds, these coordinated embryonic movements are associated with tucking, a behavior controlled by the central nervous system and crucial for hatching success. Birds unable to do so frequently don't survive.

Scientists have long believed that tuck was a peculiarity of birds, something that birds developed on their own. Baby Yingliang says otherwise.

Redefining the bird-dinosaur link
Tucking behavior, once thought to be unique to birds, may have originated in theropod dinosaurs tens or hundreds of millions of years ago, according to a study led by researchers at the University of Birmingham and China University of Geosciences.

That’s a seismic shift. Think of it this way: the same instinct that tells a baby chick how to orient itself inside an egg on an Iowa farm could have roots that reach back to the Cretaceous period, long before the first true bird ever took flight.

It “looks just like a baby bird all curled up in its egg,” said Steve Brusatte, a paleontologist at the University of Edinburgh and a member of the research team. It’s “yet more evidence that many features characteristic of today's birds first evolved in their dinosaur ancestors.”

Baby Yingliang is one of a group of dinosaurs called oviraptorosaurs, feathered theropod dinosaurs with beaks and hollow bones that lived in Asia and North America, the paper, published in iScience, said. They were already among the closest relatives of today’s birds among dinosaurs. This fossil makes that connection even stronger.

What makes this fossil so rare
Dinosaur embryos are one of the rarest kinds of fossils to find in good condition. Very small, delicate bones tend to scatter or disintegrate well before they can be preserved. Baby Yingliang is one of the best-preserved dinosaur embryos ever reported because it is articulated in its life position with little disruption from fossilization.

Most known non-avian dinosaur embryos are incomplete and disarticulated skeletons, so the discovery of Baby Yingliang, beautifully preserved and lying in a bird-like posture, was a genuine surprise for the team, according to research from the University of Birmingham.

What comes next
Scientists are far from done with Baby Yingliang. Imaging techniques will be used to study internal anatomy still encased in rock, skull bones and body parts not yet fully exposed. The researchers also hope to find more embryo fossils so they can test whether this tucking posture was common among oviraptorosaurs, or even across wider groups of dinosaurs.

Right now, a tiny fossil in a Chinese museum is quietly rewriting the story of how life prepares to enter the world, a story that turns out to be much older than any of us realized.