Strontium isotope composition of skeletal material can determine the birthplace and geographic mobility of humans and animals

The Sr isotope composition measured in skeletal elements (e.g., bone, teeth , or antlers) can be used to infer the geographic region that an animal or human inhabited, because different regions tend to have distinct Sr isotope compositions, and natural variations in the relative abundance of Sr isoto pes are not changed as Sr is processed through the food chain. Therefore, a n organism that ingests Sr from one region can have a Sr isotope compositio n that is different than that of an organism that ingests Sr from another r egion. The Sr isotope composition of skeletal elements is a reflection of t he concentration-weighted average of dietary Sr that was ingested while tha t skeletal element was produced. Because different skeletal elements grow a nd exchange Sr at different stages during the life times of organisms, Sr i sotope analysis of different skeletal elements can be used to infer changes in geographic location at different stages in an organism's life. The Sr i sotope compositon measured in human teeth will reflect the average Sr isoto pe composition that was ingested as a child, due to the immobile nature of Sr and Ca in teeth after formation, whereas the Sr isotope composition of b one will reflect the average isotopic composition over the last ten years o f life, due to continuous biological processing of Sr and Ca in bone. Infer ring the average isotopic composition of dietary Sr is best done by analyzi ng skeletal fragments from control groups, which might be animals that have the same feeding habits as the animal in question, or, in the case of huma ns, analysis of close family relatives. In cases where it is not possible t o construct a Sr isotope database from control groups, it becomes necessary to estimate the isotopic composition of dietary Sr based on geologic princ iples. We present three case studies from our research that illustrate a ra nge of approaches: (I) results from a criminal case where a deer was illega lly harvested and the location of the deer was important to establish, (2) a pilot study of commingled human remains from a burial in Vietnam, associa ted with the Vietnam Conflict, and (3) a study of 13th and 14th century mig ration of people from an archeological site in the Southwest United States.