At a glance, without looking at pictures for detailed comparison, the spirals remind me of some depicted in one of Marija Gimbutas' books on Old Europe (in the archaeological sense, not the Rumsfeldian sense, LOL) which she interprets in terms of birth symbolism related to earth goddess imagery, i.e. the spiral represents the descent into the "womb" of the earth/underworld. There are also similar spirals in Asian and Mesoamerican art, representing a stylized Yin/Yang shape, but there the end of the spiral typically has a more pronounced right angle at the whorl tip than what I see here.
The writings about Newgrange all remark on the similarity of other passage tombs found in Spain and Portugal. I think that there is no doubt that many ancient peoples were connected in some way.