(very on mushrooms voice) dragons are probably related to centaur given how these are the only two notable species that have a 6-limbed symmetrical structure as opposed to the traditional arm/leg paradigm. dragons being coldblooded and lizardlike is probably an example of convergent evolution, perhaps scales being an adaptation to sliding more smoothly through gold piles and having better aerodynamics, with the coldblooded aspect suiting the isolated long-term hibernation/stasis cycles.