Timber circles may have had "lintels " and considering the reference to wood in the stonehenge architecture this could have been a source of inspiration .
Despite having suggested you can't put percentages on unknowns I reckon it's 99.999% certain there were pre-existing Stonehenge-type timber monuments.
You'd have to be seriously tapped to construct tongue and groove and mortise and tenon joints in massive sarsens without having first learned to create them in wood!
Well for a start they are hardly mortise and tenon joints in the true sense of the joint are they. At best they are stub tenons and very small ones at that. I'm a carpenter/joiner by profession and to create a true mortise and tenon out of stone where the tenon goes right through the adjoining stone using other stones as tools is pushing their skills too far.