Oviraptorosaurs are a well-defined group of coelurosaurian dinosaurs characterized by short, deep skulls with toothless jaws, pneumatized caudal vertebrae, anteriorly concave pubic shafts, and posteriorly curved ischia. The most basal forms were small, similar to a chicken or a turkey, and like extant birds, they had pennaceous feathers. Their fossil record span much of the Cretaceous of Asia and North America. The most famous dinosaur of this group, Oviraptor, was discovered in 1923 by Roy Chapman Andrews in Mongolia, associated with a nest of what was thought to be Protoceratops eggs. The misconception persisted until 1990s when it was revealed that the eggs actually belonged to Oviraptor, not Protoceratops. Since then, more skeletons of Oviraptor and other oviraptorids like Citipati and Nemegtomaia have been found brooding over their eggs. Oviraptorids also have the best record of embryonic fossils. A new specimen, from the Late Cretaceous Hekou Formation of southern China, represents the most well-preserved dinosaur embryo ever discovered, and exhibits a posture of a late-stage modern bird embryo. This new finding suggests that avian tucking behavior possibly originated among non-avian theropods.
The new specimen (YLSNHM01266), nicknamed Baby Yingliang, is preserved curled inside its egg, with the head positioned ventral to the body. The oviraptorid affinity of Baby Yingliang is supported by several characers, including the crenulated ventral margin of premaxilla; the edentulous skull; the U-shaped mandibular symphysis; and the highly arched dentary. The vertebral column is estimated to have 22 presacral vertebrae. The pubis points posteroventrally, similar to that of modern birds, althought it is unclear how much of its orientation is genuine.
The almost complete skeleton is ∼23.5 cm in total length. It was found in Shahe Industrial Park in Ganzhou City and acquired by the director of Yingliang Group, Mr Liang Liu. It was stored in Yingliang Stone Nature History Museum until the museum staff discovered it.
Waisum Ma et al. (2021). An exquisitely preserved in-ovo theropod dinosaur embryo sheds light on avian-like prehatching postures, iScience DOI: https://doi.org/10.1016/j.isci.2021.103516
Bi, Shundong, et al. (2021). An oviraptorid preserved atop an embryo-bearing egg clutch sheds light on the reproductive biology of non-avialan theropod dinosaurs. Science Bulletin, 66(9), 947-954 https://doi.org/10.1016/j.scib.2020.12.018