Rare dinosaur embryo shows bird-like posture

An exquisitely preserved embryo, found inside a fossilised dinosaur egg, sheds new light on the link between the behaviour of modern birds and dinosaurs, according to a new study.

The 72 to 66 million-year-old embryo – dubbed ‘Baby Yingliang’ – belongs to a two-legged, toothless theropod dinosaur thought to have roamed Asia and North America.

The fossil was discovered in Cretaceous rocks, found in the Ganzhou region of southern China.

Bird-like posture

Among the most complete dinosaur embryos ever found, the fossil suggests that these dinosaurs developed bird-like postures close to hatching.

Scientists found the posture of Baby Yingliang unique among known dinosaur embryos. Its head lies below the body, with the feet on either side and the back curled along the blunt end of the egg. Previously unrecognised in dinosaurs, this posture is similar to that of modern bird embryos.

Tucking

In today’s birds, such postures are related to tucking — a behaviour controlled by the central nervous system and critical for hatching success. After studying egg and embryo, researchers believe that such pre-hatching behaviour, previously considered unique to birds, may have originated among these non-avian dinosaurs, millions of years ago.

Additional discoveries of embryo fossils would be invaluable to further test this hypothesis.

Fossilised egg

The research team, led by scientists from the University of Birmingham, China University of Geosciences, Beijing and palaeontologists from Edinburgh published their findings in iScience.

They found that the embryo was fixed in its position without much disruption from fossilisation. Estimated to be 27 cm long from head to tail, the creature lies inside a 17-cm-long elongated fossilised egg.

Identification

Baby Yingliang was identified as an oviraptorosaur based on its deep, toothless skull.

Oviraptorosaurs are a group of feathered theropod dinosaurs, closely related to modern-day birds, known from the Cretaceous period in Asia and North America- said to have begun 125 million years ago.

Their variable beak shapes and body sizes are likely to have allowed them to adopt a wide range of diets – including plants and meat.

The fossil is housed in Yingliang Stone Nature History Museum in Xiamen, Southeast China.

This dinosaur embryo inside its egg is one of the most beautiful fossils I have ever seen. 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.
Professor Steve Brusatte
Senior author and Personal Chair of Palaeontology and Evolution, University of Edinburgh

Dinosaur embryos are some of the rarest fossils and most of them are incomplete with the bones dislocated. We are very excited about the discovery of 'Baby Yingliang' - it is preserved in a great condition and helps us answer a lot of questions about dinosaur growth and reproduction with it.

"It is interesting to see this dinosaur embryo and a chicken embryo pose in a similar way inside the egg, which possibly indicates similar prehatching behaviours.
Fion Waisum Ma
Joint first author and PhD researcher, University of Birmingham

This dinosaur embryo was acquired by the director of Yingliang Group, Mr Liang Liu, as suspected egg fossils around the 2000. During the construction of Yingliang Stone Nature History Museum in 2010s, museum staff sorted through the storage and discovered the specimens.

“These specimens were identified as dinosaur egg fossils. Fossil preparation was conducted and eventually unveiled the embryo hidden inside the egg. This is how ‘Baby Yingliang’ was brought to light.
Professor Lida Xing
Joint first author of the study, China University of Geosciences, Beijing