Perhaps even more intriguing is a single shell with what appears to be a geometric pattern—zigzagged grooves carved into the center of the outer shell. Analysis points to the patterns being carved on purpose. Again the team turned to modern mussels; they tried carving similar patterns into Potamida littoralis with a shark tooth and compared that to weathering and natural abrasions. Sure enough, their carvings were the closest matches to the ancient pattern. “That must have been an appealing thing for Homo erectus,” says Joordens. “You can imagine sitting there with a shell in one hand and a tool in...