I recently reread the wonderful book Big Bird! Modern Sightings of Flying Monsters by Ken Gerhard and it sparked an interesting question in my mind; if, as we suspect according to paleontology, pterosaurs had pyncofibers (similar to a cross between feathers and fur) on their bodies, why do we not get more reports of anomalous birds and flying reptiles with such structures?
From what I can tell, there is no evolutionary reason for pyncofibers to have been lost through time. They would have simply improved over time.
This leaves us with a couple possibilities;
First, maybe the sightings aren't of pterosaurs. This is quite a likely possibility, animals flying through the sky can distort their appearance and maybe make them look like something one would described as pterosaurs. Places where most Thunderbird sightings occur, do have their own fair share of known large birds, Texas is an excellent example.
Second, maybe the creatures are zooforms. This is a possibility which is gaining more attention and support. Physical animals of that size remaining hidden, especially ones that fly, for so long in populated areas are extremely unlikely. Non-physical apparitions seems slightly more likely.
Thirdly, maybe what people are seeing actually are pterosaurs and I am completely wrong.
Let me know in the comments what you think!