maritime diffusion of megalithic culture

Stonehenge mystery solved? Prehistoric French may have inspired it and other European megaliths. These researchers propose that the Brittany region of northwest France is the origin point 7,000 years ago for megalithic culture (meh) and that it spread through maritime diffusion, which seems plausible.

Over an exhausting 10 years, Schulz Paulson created a "megalith evolution" using radiocarbon dating of more than 2,000 historic sites across Europe. "We have thus been able to demonstrate that the earliest megaliths originated in northwest France and spread along the sea routes of the Mediterranean and Atlantic coasts in three successive principal phases," she wrote in the study.

Huh. How would the stone circles of Western Sahara fit into this? 

I need to look up the dates of the three phases.