I read a book series about 15 years ago. It’s about these humanoid dinosaurs, I think the covers were red, green and blue, one of the main characters was a triceratops. And I think the flying and swimming dinosaurs had disappeared and where believed to have died out.
They also had like coloured armour and weapons.
I think each cover was a different colour and had a circle in the middle with one of the dinosaurs in it wearing coloured armour and holding a weapon to match.
I also think that the three dinosaurs were in a castle or something, and they found statues of flying dinosaurs.