Talk: Dragon egg
Speculation about the origin of Daenerys' eggs
I don't expect that we will have more than circunstantial evidence, but the best guess for how come Illyrio Mopatis found three dragon eggs, fossilized or otherwise, seems to be that they were clutched by Vhagar (or perhaps Caraxes) during the period between 115-120 AC when Laena Velaryon and Daemon Targaryen were in Essos. It is explicitly said that they were in Pentos for a fair while, enough for both their daughters to be born there. There would be very few and no better opportunity for dragon eggs to be clutched and end up in Pentos in the known history since Aegon's Landing in Westeros.
From what we learn in The Princess and the Queen it would seem that Moondancer, Stormcloud, Morghul and Shrykos did not grow particularly quickly during the two years of the Dance of the Dragons, and we know that the last living dragon lived long enough to lay a clutch of five eggs of her own and to be seen by Ser Arlan Penntree, but not to grow anywhere near the size of Daenerys' own.
It is also implied that very few dragons ever approached the size of the fully grown Balerion, the known exceptions being Vhagar and perhaps Vermithor. Moondancer had grown only to about the body size of a warhorse during the final days of the Dance, when she must have been at least two years old, and at a time when Baela Targaryen had apparently developed a fairly good rapport with her. The books seem to imply that Daenerys' dragons did not remain at that size for very long at all.
By contrast, all three of Daenerys' dragons seem to be fast growers, being battle-worthy after about four or five years from their hatchings. That might perhaps hint that they are the offspring of a dragon of above-average size, and that again points towards Vhagar. LuisDantas 05:25, 9 March 2015 (UTC)