 A system of hook-like uncinate processes on the ribs as with the Maniraptoriformes, allowing the ribcage to move flexibly, in articulation with an ossified sternum, was absent in "Scipionyx".The holotype of "Scipionyx" is a rare example of a non-avian theropod hatchling; the most important other very young specimens are the chicks of "Byronosaurus" that however are much less complete.The young age is reflected by the proportions and the low degree of ossification and fusion of several skeletal elements.