Tracking mammoths and mastodons: Reconstruction of migratory behavior using strontium isotope ratios

Variations in the strontium isotope ratio (⁸⁷Sr/⁸⁶Sr) of tooth enamel are used to examine the migration patterns of late Pleistocene mammoths and mastodons from Florida. An animal's ⁸⁷Sr/⁸⁶Sr ratio tracks the ratios of its environment, which vary with differences in bedrock and soil. Consequently, the environmentally controlled differences in ⁸⁷Sr/⁸⁶Sr ratio recorded in mineralized tissue, such as tooth enamel, may be used to reconstruct the movement patterns of an individual. We map variations in local ⁸⁷Sr/⁸⁶Sr ratios across modern Florida and Georgia through analysis of rodent teeth, plants, and surface water, then use this map to interpret the movement patterns of extinct mammals. Mastodons from northern and central Florida have higher ⁸⁷Sr/⁸⁶Sr ratios than both modern environmental samples from Florida and fossils from nonmigratory species, suggesting that mastodons migrated north into Georgia. Mammoths display ratios similar to those of environmental samples and resident species, suggesting that they did not migrate outside Florida.