Marine strontium isotopes preserved in fossil shark teeth calibrate Neogene land mammal evolution

Abstract

Many Cenozoic terrestrial fossil sites worldwide rely on land mammal evolution (biochronology) for temporal calibrations. Within marine depositional environments, strontium isotope compositions from invertebrate fossils are often used for enhanced temporal resolution. Here we demonstrate that strontium isotope ratios from fossil shark tooth enameloid can quantitatively calibrate ages at sites containing both marine and non-marine fossils. Analysis of REEs in the same samples provides data for understanding the taphonomic histories of the specimens and allows for identification of specimens that were likely reworked. Using Neogene shark teeth, we resolve a ∼ 600,000-year age difference between two late Miocene Florida sites previously binned together within the latest Hemphillian (Hh4) North American Land Mammal Age (NALMA) based solely on biochronology. This refinement brackets the Nme2 sea level lowstand, providing further calibration for the Great American Biotic Interchange (GABI) between South and North America. These examples emphasize the significance of strontium isotope ratios preserved in fossil shark teeth for global Neogene calibrations, especially in sites with marine/non-marine intercalations.