in early writings, Morgoth did some experiments on eagles in order to obtain the ability to fly. although he was not successful at first, perhaps he may had finally achieved that goal. but I also think that Morgoth also did some experiments on some reptiles. I don't know how he managed to apply flight ability to his dragons, though. I mean, it's clear to me that he at some point did some experiments on eagles and lizards and the winged dragons resulted from that.