So many pigs

[Maeran]

I'm not going to pretend to be an expert, but will give a quick comment.
Animal bones are a common part of archaeological debris, from food and ritual deposits (e.g. burials of entire horses and dogs alongside human burials). As such you can probably get a lot of information regarding the general size and approximate 'type' of ancient breeds.

A quick search suggests that a lot of DNA work has been done on ancient livestock, but most of what I found was more concerned with the Neolithic origins of domestic cattle.
Quite a lot of surviving breeds are described as ancient, but it might be hard to verify that claim. I know that people argue about exactly what a Mollossian hound actually was, for example.