Mayan art and calendar at Xultunstunarchaeologists
The site, in Guatemala, includes the first known instance of Mayan art painted on the walls of a dwelling.
A report in Science says it dates from the early 9th Century, pre-dating other Mayan calendars by centuries.
Such calendars rose to prominence recently amid claims they predicted the end of the world in 2012.
The Mayan civilisation occupied Central America from about 2000BC until its decline and assimilation following the colonisation by the Spanish from the 15th Century onwards. It still holds fascination, with many early Mayan sites still hidden or uncatalogued.
The ruins at Xultun were first discovered in 1912 and mapping efforts in the 1920s and 1970s laid out much of the site's structure.