There's an old ( Ancient?) story I recall from a collection, but not well enough to locate on Google ( It keeps giving me biographies of cardiac transplant surgeons ). A famous British IIRC surgeon pioneers corrective surgery for heart defects. the narrator of the tale, a close friend of the surgeon, points out to him that an alligators hearts could be thought of as "deformed" in ways when compared to other animals even among reptiles. The surgeon speculates if this could be a true mutation deformity and sets out to "correct" it surgically in a group of test subjects. The alligators survive, and like neotonous animals exposed to hormones, grow further, sprout wings, and literally become dragons. Anyone recognize the story?
This is The Day of the Dragon, by Guy Endore. (He's credited as "Guy Endor" in the linked reproduction but appears as "Endore" on Wikipedia and IMDb.) A Professor Crabshaw endeavors to cure alligators' congenital heart conditions:
"'Well,' Crabshaw went on before I could interrupt, 'it occurred to me one day to see what would happen if that bad heart condition of the alligator were cleared up or at least improved by stretching that incomplete septum to form a dividing wall between the venous and the arterial blood streams."
Clever readers might predict the outcome: The "cured" gators grow into dragons!
"There were my beasts, growing larger every day, greater now then elephants in the bulk of their torso and the parasol-like growth on their backs expanding and expanding, and shaping itself out into two vast ovals, one on each side. Then, on day, it came to me, suddenly, what these were: wings! Yes, sir, wings!"
Crabshaw's well-intentioned endeavor has some unfortunate effects:
"Too late then to fight the vermin that had obtained such a foot hold in our world. Alas - no longer our world, but the world of the dragons who have become supreme!"