The embryo that was preserved for at least 66 million years ago was about to hatch into a chicken, according to scientists.
The fossil was found in southern China and was called "Baby Yingliang" by the researchers.
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The dinosaur was armed and dangerous.
Dinosaur-chicken-hell-anzu-WYliei is a story from The Guardian.
Fion Waisum Ma, a researcher at the University of Birmingham, said that it was one of the best dinosaur embryos ever found.
Ma and colleagues found a dinosaur with its feet on either side and back curled, a posture that was previously unseen in dinosaurs but similar to modern birds.
The central nervous system in birds controls the behavior. The chick needs to tuck her head under her right wing in order to hatch.
There is a higher chance of death from failed hatching. Ma said that such behavior in modern birds first evolved from their dinosaur ancestors.
An alternative to tuck could have been a sitting posture with the head resting on the chest.
The illustration shows a close-to-hatching oviraptorosaur dinosaur embryo. The University of Birmingham is pictured.
During the Late Cretaceous period, Oviraptorosaurs were feathered dinosaurs that lived in Asia and North America.
They ranged in size from small turkeys at the lower end to giant Gigantoraptors, which were eight metres (26ft) long.
The baby is 27 cm long from head to tail and 17 cm long inside an egg at the museum.
The creature is thought to be between 72m and 66m years old, and was probably preserved by a mudslide that buried the egg.
If it had lived to be an adult, it would have grown to three metres. The specimen was forgotten in storage for decades.
The research team suspected they may have an unborn dinosaur and removed part of Baby Yingliang's eggshell. Prof Steve Brusatte of the University of Edinburgh, part of the research team, said that the dinosaur embryo inside its egg is one of the most beautiful fossils he has ever seen.
This little dinosaur looks like a baby bird curled in its egg, which is evidence that many features of today's birds first evolved in their dinosaur ancestors.
The team hopes to use advanced scanning techniques to image the full skeleton of Baby Yingliang, which is still covered in rock.
