You do bring a valid point about pterosaurs, Vampirehunter.
The defining line between what is a reptile and what isn't a reptile is still rather vague to me. The main characteristics of a reptile are:
-They're vertebrates
-They're cold-blooded
-They (mostly) lay eggs
-They breathe oxygen using lungs
-They have dry scaly skin
It just sounds to me to be so undefined compared to many other classes. Things like "they mostly lay eggs" is rather "well kinda, sorta this is what makes a reptile".
Many paleontologists are even questioning if dinosaurs were cold-blooded or not. Which means they too will no longer fit into the definition of a "reptile".
Certainly it is already difficult to classify extinct animals, but it's even worse trying to classify an animal when no solid evidence is available that they even existed.