Pre-pottery farmers on the Pacific coast of southern Mexico

Large island-like shell mounds along the southern coast of Mexico are the earliest known archaeological sites on the Pacific margin of Mesoamerica. These aceramic deposits date to between 7500 and 3800 cal BP and have been interpreted as locations where foragers, living elsewhere seasonally on the coastal plain, harvested shellfish and other estuarine resources. Based on an accumulation of paleoecological data from elsewhere in the lowland Neotropics of Mesoamerica, southern Central America and South America we pose and provide a first test of an alternative subsistence model: that the Archaic Period populations in this area were slash and burn farmers. Burned maize phytoliths first appear in these sedimentary records at 6500 cal BP in association with macroscopic charcoal and forest disturbance plant taxa. Periodic burning and forest disturbance, consistent with farming activities, are also evident in the macroscopic charcoal record between 6500 and 4700 cal BP. Pollen, phytolith and charcoal records all point to sustained burning, forest disturbance and the cultivation of maize between 4700 and 3800 cal BP. These data suggest that people were slash and burn farming during the Archaic Period prior to the adoption of pottery and the proliferation of Early Formative Period villages and full-fledged agriculture based on near or total reliance on crop plants after ∼3800 cal BP.