Some of the birds that went extinct, the enantiornithines, were actually more common than and out-competed modern bird ancestors.
The 75-million-year-old fossil, from a bird about the size of a turkey vulture, is the most complete skeleton discovered in North America of what are called enantiornithines (pronounced en-an-tea-or'-neth-eens), or opposite birds.
Atterholt and Hutchison collaborated with Jingmai O'Conner, the leading expert on enantiornithines, to perform a detailed analysis of the fossil.
"What this new fossil shows is that enantiornithines, though totally separate from modern birds, evolved some of the same adaptations for highly refined, advanced flight styles."
The fossil's breast bone or sternum, where flight muscles attach, is more deeply keeled than other enantiornithines, implying a larger muscle and stronger flight more similar to modern birds.
If enantiornithines in the late Cretaceous were just as advanced as modern birds, however, why did they die out with the dinosaurs while the ancestors of modern birds did not?
"One of the really interesting and mysterious things about enantiornithines is that we find them throughout the Cretaceous, for roughly 100 million years of existence, and they were very successful.
The new species, which the Chinese paleontologists named Protopteryx fengningensis, is the most primitive known among the birds called enantiornithines
. This group at one time included the majority of birds but became extinct by the end of the Cretaceous period 65 million years ago.