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

Variations in the strontium isotope ratio (Sr-87/Sr-86) of tooth enamel are used to examine the migration patterns of late Pleistocene mammoths and ma stodons from Florida. An animal's Sr-87/Sr-86 ratio tracks the ratios of it s environment, which vary with differences in bedrock and soil. Consequentl y, the environmentally controlled differences in Sr-87/Sr-86 ratio recorded in mineralized tissue, such as tooth enamel, may be used to reconstruct th e movement patterns of an individual. We map variations in local Sr-87/Sr-8 6 ratios across modern Florida and Georgia through analysis of rodent teeth , plants, and surface water, then use this map to interpret the movement pa tterns of extinct mammals. Mastodons from northern and central Florida have higher Sr-87/Sr-86 ratios than both modern environmental samples from Flor ida and fossils from nonmigratory species, suggesting that mastodons migrat ed north into Georgia. Mammoths display ratios similar to those of environm ental samples and resident species, suggesting that they did not migrate ou tside Florida.