No such similarities are perceptible in Celtic or Megalithic culture.

The similarities are certainly perceptible in terms of general & academic conjecture that has the Shamanic impulse (to some as innate as language & sexuality) as the universal root impulse of human religiosity. There are plenty who insist that it's behind the abstract / non-figurative nature of Beaker rock art, itself based on a vocabulary which at least implies a widespread belief system, albeit with regional dialects, throughout Northern Europe & the UK. Some would see it in the Gundestrup Cauldron, the patterns of the Lindisfarne Gospels and even the miraculous life of that celebrated Shaman Saint Cuthbert himself - who interceded with the elements & animals as a matter of daily daliance. The art of the Herefordshire Romanesque betrays a lot of such influences, which carries on from Norse Pagan influences into Norman Xtian culture, which itself draws on ideas from further afield (though a lot more immediate than the Siberian migrations into the Americas) see Kilpeck etc.

Time to dig out my copy of Eliade...