ill put this new theory of mine out here, its quite original, and people give it positive responses. http://asoiaf.westeros.org/index.php/topic/125649-azor-ahai-and-the-sphinx/ Ill put a TLDR here: TLDR: Dragons are the biological sum of 3 creatures, Nagga the serpent or firewyrm, a great lion, and a big Vale bird. they were created by Azor Ahai. The 3 parts of the AA story is a parallel to the 3 base ingredients that makes a dragon, so is the remark that the dragon has 3 heads. The oldtown sphinxes were incubators used by AA to produce this biological mix, and Valyrian sphinxes are later models derived from the Oldtown ones, and thats how dragons get raised from stone.