THE POSSIBILITY OF PRONGHORN TEETH AS SEASONALITY INDICATORS FOR PALEOCLIMATE RECONSTRUCTIONS

Seasonality of the hydrologic system plays an important role in determining ecological structure, composition, and interactions within terrestrial ecosystems. Stable oxygen isotope composition of precipitation is a critical component of the ecohydrolgy and often used as a climate indicator in modern and paleontological studies. In addition, global climate models are increasingly incorporating δ¹⁸O values of meteoric waters as tracers, which can be compared to empirical data. In modern systems, δ¹⁸O in meteoric water can be assessed directly via sample collection or in situ measurements, but reconstruction of hydrological cycles in the past requires the use of indirect proxies (i.e., shells, teeth, tree ring cellulose, ice cores, etc.). Here, we explore the possibility of tooth enamel from pronghorn (Antilocapra americana Gray, 1866) as a recorder of paleoclimate seasonality. We serially sampled the third lower molars of modern and historical pronghorn from Wyoming for oxygen isotope composition in phosphate (δ¹⁸O_PO4) and compared patterns to: (1) interpolated and (2) measured yearly variation in central Wyoming environmental waters (δ¹⁸O_w) using the US Network for Isotopes in Precipitation (USNIP) as well as to (3) δ¹⁸O values from sagebrush leaves, lakes, and rivers in the same region. These comparisons allowed us to evaluate inputs of leaf vs. meteoric water to pronghorn body water. We find that pronghorn teeth are ¹⁸O-enriched, similar to plant leaf water, and preserve more of the seasonal hydrological signal than ungulates, likely due to comparatively rapid enamel mineralization. Our modern and historical data therefore suggest that pronghorn teeth are a viable substrate to reconstruct δ¹⁸O seasonality in paleoclimate studies, especially in semi-arid and arid habitats that are not favored by other ungulate species.