Marine foods have different carbon isotope ratios than terrestrial foods, because the carbon in marine organisms comes from a different source than the carbon in terrestrial organisms.

Nitrogen isotope ratios increase with each step up the food chain — predators have higher nitrogen isotope ratios than their prey.

By measuring the carbon and nitrogen isotope ratios in the collagen of Shuká Káa’s bones, researchers could determine both the primary source of his diet (marine versus terrestrial) and his position in the marine food chain.

The results indicated a primarily marine diet, with protein derived from organisms high in the marine food chain — consistent with consumption of marine mammals, large fish like salmon, and other high-trophic-level marine species.

The ancient DNA work required the additional steps of extracting and sequencing the genomic material preserved in the remains.