Homo erectus. The zig zag pattern, that can only be seen with oblique lighting, is clearly older than the weathering processes on the shell arising from fossilization. These early human-like people drilled a hole through the shell using a sharp object, possibly a shark's tooth, exactly at the point where the muscle is attached that keeps the shell closed. "The precision with which these early humans worked indicates great dexterity and detailed knowledge of mollusc anatomy." click through
