1. This date is given for two solid rubber balls excavated at the Manatı́ site in Veracruz Mexico [C. Rodriguez and P. Ortiz El Manatı́ un Espacio Sagrado de los Olmeca (Universidad Veracruzana Jalapa Veracruz Mexico 1994)].
2. C. Coggins and J. Ladd in Artifacts from the Cenote of Sacrifice Chichén Itzá Yucatán C. Coggins Ed. (Peabody Museum of Archaeology and Ethnology Harvard Univ. Press Cambridge MA 1992) pp. 353–357.
3. T. Leyenaar and L. Parsons Ulama The Ballgame of the Mayas and Aztecs (Spruyt Van Mantgem and De Does Leiden Netherlands 1988); V. Scarborough and D. Wilcox The Mesoamerican Ball Game (Univ. of Arizona Press Tucson 1991).
4. D. Tedlock (trans.) Popol Vuh (Simon & Schuster New York 1985).
5. Castilla elastica is native to Mexico south of 21°N through northern South America. Castilla elastica grows chiefly in the state of Tabasco Yucatan and Chiapas at altitudes of 700 m or lower [P. C. Standley Trees and Shrubs of Mexico (Government Printing Office Washington DC 1920)].