Bird Evolution

There are currently 8 acknowledged Subclasses of birds. 7 of these are extinct. The subclasses that are no longer in existence are;

Archaeopteryx (a group with just this single representative)
Alvarezsauridae
Iberomesornis
Enantiornithes
Patagopteryx
Hesperornithiformes
Ichthyornithiformes

The only existing group of birds is the subclass Neornithes.