Late Cretaceous fossil birds are rare. When found, they are usually very incomplete hindering attempts to understand broad trends in avian evolution across the Cretaceous.
The best-preserved Late Cretaceous enantiornithine known to date.
The holotype of Yuornis represents the best-preserved Late Cretaceous enantiornithine known to date. The specimen consists of a complete 3D skull together with a partial postcranial skeleton. While the postcranial skeleton reveals features typical of enantiornithines and very different than in modern birds, the skull reveals that by the Late Cretaceous enantiornithines had evolved a number of features in parallel to modern birds such as the reduction of the lacrimal, loss of the postorbital, and an edentulous rostrum.