1 of 8

Mystery HolesWorkers clean a 4,300-year-old clay floor at the Tlacuachero archaeological site in Mexico's Chiapas state (see map) in February 2009.Mysterious semicircles of holes (center and lower right) in the floor may be dice scoreboards, archaeologist Barbara Voorhies, a professor emerita at the University of California, Santa Barbara, said recently. (Get the full story.)If so, the circles are the oldest known evidence of games in Mesoamerica, a region that stretches from Mexico to Costa Rica.In 1988 Voorhies found the buried floor under a mound created by the Chantuto people, foragers who lived along the coast of what's now southern Mexico between about 3,500 to 7,500 years ago.(See "16 Indian Innovations: From Popcorn to Parkas.")In 2009 she found another clay floor just below the pictured floor—as well as portions of nine other semicircles. A historical account Voorhies discovered in 2009 revealed that the circles have a "striking similarity" to other Native American gaming boards."There's no absolute proof that my interpretation of these strange features [is right]," she said. "But it's a very strong analogy, and that's about as good as it gets for archaeology."Voorhies received funding for her research from the National Geographic Society's Committee for Research and Exploration. (The Society owns National Geographic News.)—Christine Dell'Amore

Photograph courtesy Barbara Voorhies