"By the early Cretaceous, some pterosaurs (by the process of cladogenesis), had developed into flying dromaeosaurids and troodontids".By accepted cladistic thinking this is a perfectly reasonable and common type of occurrence. A subset of creatures develops a set of changes that sets them apart from the original group. They exist in their own ecological niche. In this case, some pterosaurs develop feathers and hand bones characteristic of dromaeosaurids and troodontids (such that they are now recognized as dromaeosaurids and troodontids).
If this sounds at all unusual, just realize that this is exactly the process that evolution theory posits for all evolutionary changes. And by the process of cladogenesis the new creatures and the original creatures co-exist.
And the next step:
"By the late Cretaceous, many of these flying dromaeosaurids and troodontids had developed into a variety of modern flying birds (Neognaths)."
This is the same process again. Here the dromaeosaurids and troodontids lose their primitive bird characteristics such as teeth (if they have them) and develop other modifications, developing into modern birds. In this case they develop into a variety of neognaths (not paleognaths) because they are flying creatures.
Again this is perfectly acceptable cladistic thinking.
In the next post I will analyze the concurrent origin of flightless birds from other flying dromaeosaurids and troodontids during the Cretaceous.