Back in a land before time, many dinosaurs laid eggs. With parents guarding their clutches, tiny baby dinosaurs might eventually emerge from incubating embryos. Yet this process is only occasionally captured in the fossil record. Fossils of nesting dinosaurs atop eggs, or of complete egg embryos, are quite rare. However, a fully articulated dinosaur embryo was discovered inside a fossilized egg held by a Chinese museum, according to a paper published in iScience in 2021.
The fossilized egg was found in the collections of Yingliang Stone Natural History Museum, which acquired it around 2000. Later, investigations into the collection identified the egg as what it was. Further research discovered a shockingly complete, exceptionally well-preserved dinosaur embryo inside. The specimen is between 66 and 72 million years old. Professor Steve Brusatte, an author of the study, said in a statement, “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.”
In fact, the dinosaur's posture suggests it was close to hatching. It is a type of feathery theropod called an oviraptorosaur, and it's about 10.6 inches long. Curled within its shell, it has assumed a posture called “tucking” which birds such as modern chickens likewise assume before birth. According to the study, the critter's head is “ventral to the body, with the feet on either side, and the back curled along the blunt pole of the egg.” This “previously unrecognized [posture] in a non-avian dinosaur” suggests modern birds may in fact have inherited this “tucking” maneuver from their dinosaur ancestors. “Baby Yingliang,” as the egg is known, is just the beginning of what researchers may soon discover about feathered ancestors.
A fully articulated dinosaur embryo was discovered inside a fossilized egg in the Yingliang Stone Natural History Museum in Xiamen, China.
h/t: [IFL Science]