According to the current scientific consensus, all dinosaurs hatched from eggs. Some of these eggs had hard shells, like those of modern birds, whereas others were soft-shelled, similar to those of reptiles. However, most of the nesting sites discovered by paleontologists contained either eggshells alone or fragmented fossils of dinosaur embryos.
The recent discovery of the perfectly preserved egg fossil affectionately called “Baby Yingliang” changed everything, as it shows the exact position of an oviraptorosaur fetus and confirms an uncanny resemblance to modern birds.
The 66-72 million-year-old egg was unearthed in 2000 near the city of Ganzhou in China. It was held in storage for 15 years, but the preparation of the fossil for display at the Yingliang Stone Natural History Museum in Xiamen revealed its long-kept secret.
Researchers noticed a bone visible through a crack in the shell. Splitting the egg in two revealed a perfectly-preserved skeleton of an oviraptorid fetus - only a few days from hatching. The baby dino was almost 11 inches (27 cm) in length from beak to tail, but it was neatly curled up in a 6.7-inch (17 cm) egg.
If it had hatched and grown to maturity, Baby Yingliang would become a bird-like feathered dinosaur called an oviraptorosaur. These ostrich-like dinosaurs had hollow bones, three-toes on each leg, a toothless beak, and grew to be around 6 feet long (1.8 m). Much like a modern bird, these dinosaurs would sit on the nests and protect the eggs until the hatchlings emerged.
According to a scientific paper published in iScience very recently, Baby Yingliang is curled up in a position reminiscent of modern birds like chickens. The skeleton displays a “tucked” posture: the head lying on its abdomen tucked under the right wing and the legs on the sides of the head. Tucking allows birds to place their beaks in such a position that it makes it easy for them to break out of the shell. A baby chicken assumes this exact position on the 17th day of its 21-day gestation, for example.
Baby Yingliang is the first known dinosaur to show tucking. According to a statement of Fion Waisum Ma, one of the researchers of the study, "The discovery of this embryo hints that some pre-hatching behaviors (e.g. tucking), which were previously considered unique to birds, may be rooted more deeply in dinosaurs many tens or hundreds of millions of years ago."
While it’s certainly fascinating to see such a perfectly-preserve baby dinosaur fossil, the discovery has far greater implications. All things considered, it is first-hand proof that modern birds could have inherited “tucking” behavior from their dinosaur ancestors, and it further strengthens the bond between these archaic animals and the avian life of today.
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