Perfectly Preserved Dinosaur Embryo Found Inside Fossilized Egg

The 66- to 72-million-year-old specimen is one of the most complete dinosaur embryos ever found.


An exceptionally rare, fully articulated dinosaur embryo has been discovered inside a fossilized egg that had been gathering dust for over a decade in a museum storage room in China. Estimated to be between 66 and 72 million years old, this unborn specimen provides an extraordinary connection between dinosaurs and modern birds.

Classified as an oviraptorosaur, a group of feathered, toothless theropods, the unhatched dinosaur is approximately 27 centimeters (10.6 inches) long. It represents the first recorded instance of a dinosaur embryo exhibiting a posture characteristic of present-day bird embryos. In preparation for hatching, modern birds perform a series of movements called tucking, which involves curving their bodies and positioning their heads beneath their wings. Until now, the evolutionary origins of this behavior have remained uncertain.

Perfectly Preserved Dinosaur Embryo Found Inside Fossilized Egg
The oviraptorosaur embryo is known as Baby Yingliang.
Image credit: Xing et al., 2021

Detailing their findings in a 2021 paper, the researchers describe their specimen—nicknamed Baby Yingliang—as having its head “ventral to the body, with the feet on either side, and the back curled along the blunt pole of the egg.” They note that such a posture is “previously unrecognized in a non-avian dinosaur, but reminiscent of a late-stage modern bird embryo.”

Tucking is believed to be crucial for the hatching process in birds, with those failing to adopt this position facing a significantly lower chance of survival. The fact that Baby Yingliang appears to have assumed the same posture suggests that this behavior may have first emerged among the ancient theropod ancestors of modern birds.

“This little prenatal dinosaur looks just like a baby bird curled in its egg, which is yet more evidence that many features characteristic of today’s birds first evolved in their dinosaur ancestors,” study author Professor Steve Brusatte said in a statement, responding to this remarkable discovery.

Perfectly Preserved Dinosaur Embryo Found Inside Fossilized Egg
Reconstruction of a close-to-hatching oviraptorosaur dinosaur embryo, based on the new specimen “Baby Yingliang”.
Image credit: Lida Xing

Currently housed at the Yingliang Stone Nature History Museum, Baby Yingliang is among the most complete dinosaur embryos ever uncovered, offering researchers a rare glimpse at an intact baby theropod. However, as it remains the only specimen of its kind, the study authors acknowledge that definitive conclusions about dinosaur embryos cannot yet be made. They emphasize the need for further discoveries of similar fossils to confirm their hypotheses.

Despite this, they conclude that “this new exceptional fossil embryo hints that some early developmental behaviors (tucking) often considered as uniquely avian may be rooted more deeply in the theropod lineage.”

The study appears in Science.


Perfectly Preserved Dinosaur Embryo Found Inside Fossilized Egg

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