Welsh Wizard: I think you are barking up the RIGHT tree, "skull bones"
I was googling images, for 'curved fossil bone' and came across: atlas bone, (2nd cervical) vertebra - supports the first cervical (axis) which is ring-like (as in the pic) and allows the head to rotate.
I think that the curving bone is suggestive of an atlas bone... Of what though, I have no idea?????
Fossil hunting...What a rush! :)