Answer:
Animal skins
Explanation:
Artists in Europe before AD 1100 prepared animal skins like parchment or vellum as drawing surfaces.
If we are talking early early then it was because art wasn't a form of "art" it was a form of communication.
But a little later down the road, people did not understand the human body and could not paint one perfectly, and also painters loved to show perfection, as in, gold everywhere, or a kind a top a thousand bodies. Something like that. So yeah...