If an object on the battlefield becomes a copy of Primal Clay, it copies the values determined by its enters-the-battlefield replacement effect.

While not on the battlefield, Primal Clay is a 0/0 creature card. It doesn't have flying or defender.

If an object enters the battlefield as a copy of Primal Clay, it copies the values determined by its enters-the-battlefield replacement effect, but its power and toughness are determined by the copy's own enters-the-battlefield replacement effect. This can cause you to have a 3/3 creature with flying, or a 1/6 creature with flying and defender, for example.