The Draco standard

[Flavivs Aetivs]

Although I don't have the knowledge of Pre-Roman history that you two have, I must say based on the defining arguments here that the Massagetae/Saka had no link to the Dacians, they were another group of Steppe Nomads who were forced to migrate due to a varied set of changing conditions.

Where the Draco comes from? Who knows. It was probably introduced to the Dacii by steppe nomads IMO, but I am certain that it derived from cultures east of the black sea. Possibly Iranians, and if you look at the folklore east of the Aral sea there's some of Chinese influence, so chinese dragon lore could have had a part to play.