Five archaeological sites on the south coast of southern Mexico provide the earliest known evidence for human occupation of the Pacific coastal lowlands of Meso-america. These sites are essentially stratified piles of shells from tiny marsh clams that date to the third millennium BC. We interpret the sites as having been specialized locations for the procurement and processing of shrimp: the shell layers were built as pavements for sun-drying shrimp, rather than being the remains of food items as had been thought previously. Inglés