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 (modern birds). 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 (eye socket), 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 ==