Neoaves

Neoaves is a clade. It includes all modern birds (Neornithes or Aves) except Paleognathae (ratites and kin) and Galloanserae (ducks, chickens and kin).Jarvis E.D. et al. 2014 Whole-genome analyses resolve early branches in the tree of life of modern birds. Science. 346 (6215): 1320–1331. 

The implication of this is that the two exceptions  may have originated from dinobird lines other than the great mass of birds. That is not proven, but it is suggested by this taxonomy.

 References 

Category:Birds