Not sure about those but on the fossil front I found some cool ones. On the south of one of the 'D-feature' stones in the south circle is a lovely bit of petrified wood. I also found some bifurcating(?) roots on the broken faces of a few stones.
The mad thing about the natural 'cupmarks' is that they were formed as solution hollows when the sarsens were still uncemented way back (if I remember) in the Tertiary.
The sarsen's so bloody hard now not much is gonna make holes like that!
At least that's what I remember. I actually did my disertation about the geological/geomorphological aspect of the sarsens but 'twas a long time ago...