Knowing “when” things happened in the past is one the greatest challenges in archaeology, and even more so for coastal archaeological finds. At coastal sites, the radiocarbon dates of organic materials – the most reliable approach for dating prehistoric events – can be severely affected by the “marine reservoir effect” (MRE) , a process that causes organic materials to appear older than they actually are. Radiocarbon data from prehistoric shell mounds can be useful for quantifying the local MRE while establishing robust chronologies for these sites. The Sambaqui de Cabeçuda is an impressive Brazilian coastal shell mound, which preserves important paleoenvironmental and archaeological information. In a recent paper published by Alves et al. (2022), we employed an interdisciplinary approach involving stable isotopes, carbonate geochemistry, and radiocarbon dates on shell, bone and charcoal remains from the site, as well as Bayesian modelling, to derive (1) an accurate MRE offset for the region, (2) the dates of human burials, and (3) the diets of the inhumated individuals. Our model outputs revealed that the local MRE was highly negative (–263 ± 46 14C yr) and thus must be considered when calibrating local conventional radiocarbon dates derived from marine organisms (e.g. shells, fish) and human remains (collagen, apatite) whose dietary proteins were dominated by marine resources. This was the case for all the human individuals analysed in this study as stable isotopes and Bayesian Isotope Mixing Models pointed to dietary regimes with a high intake of marine proteins.