Yuornis
Yuornis ) is an extinct genus of enantiornithean bird known from the Late Cretaceous of Henan, China. It contains one species, Yuornis junchangi, named after Lü Junchang.Description
The holotype specimen is remarkably complete for a Late Cretaceous enantiornithean, possessing a three dimensionally-preserved skull and partial skeleton. Unlike most enantiornitheans, the skull of Yuornis was completely toothless and convergently similar to that of Neornithes. The lacrimal and postorbital bones are completely absent and the squamosal is strongly reduced; these losses leave the antorbital fenestra and supratemporal fenestra confluent with the orbit, also like some modern birds. Unlike modern birds, the premaxilla makes up a smaller portion of the lower edge of the snout, while the quadratojugal is unusually large and complex.Classification
The phylogenetic analysis of Xu et al. positioned Yuornis as the sister taxon to Gobipteryx, another toothless Late Cretaceous enantiornithean. This would by definition place Yuornis in the family Gobipterygidae. However, the traits supporting this relationship were all related to tooth loss, a condition which is known to have convergently evolved many times in Mesozoic bird lineages. As a result, the authors refrained from formally considering Yuornis a gobipterygid.