Mexico's archaeology institute downplays theories that the ancient Mayas predicted some sort of apocalypse would occur in 2012, but on Thursday it acknowledged that a second reference to the date exists on a carved fragment found at a southern Mexico ruin site.

Most experts had cited only one surviving reference to the date in Mayan glyphs, a stone tablet from the Tortuguero site in the Gulf coast state of Tabasco.

But the National Institute of Anthropology and History said in a statement that there is in fact another apparent reference to the date at the nearby Comalcalco ruin. The inscription is on the carved or molded face of a brick. Comalcalco is unusual among Mayan temples in that it was constructed of bricks.