The early bird catches the worm

How early did primitive birds appear? By "primitive bird" I mean feathered and flying, but not yet modern. For example the Enantiornithes were "primitive birds".

http://en.wikipedia.org/wiki/Enantiornithes
"One biogeographic study in the 1990s suggested that the distribution of enantiornithines implies a Middle Jurassic origin for the clade, but this theory has not been widely accepted by paleoornithologists; a Late Jurassic/Early Cretaceous origin is more in line with the fossil record".

Let's look at some particular finds:

http://en.wikipedia.org/wiki/Liaoningornithiformes
"Liaoningornis is a surprisingly advanced bird for the Early Cretaceous. Zhou and Hou in 2002 considered it the oldest known member of the Ornithurae. It has advanced flight, perching, and respiratory adaptations like a long, deeply keeled sternum, a pair of anterolateral processes on the sternum near the articulations with the coracoids, fused, short, metatarsals, and highly curved pedal claws indicating good perching ability. "

http://sciencemag.org/cgi/content/abstract/274/5290/1164
"Late Jurassic and Early Cretaceous birds from northeastern China, including many complete skeletons of Confuciusornis, provide evidence for a fundamental dichotomy in the class Aves that may antedate the temporal occurrence of the Late Jurassic Archaeopteryx. The abundance of Confuciusornis may provide evidence of avian social behavior. Jurassic skeletal remains of an ornithurine bird lend further support to the idea of an early separation of the line that gave rise to modern birds. Chaoyangia, an ornithurine bird from the Early Cretaceous of China, has premaxillary teeth."
(Lianhai Hou, Larry D. Martin, Zhonghe Zhou, Alan Feduccia)

So we can see that there were primitive (feathered, flying) birds in the Late Jurassic/Early Cretaceous!
Modern birds developed from those primitive birds. Modern birds did not develop from dinosaurs.