Enamel Maturation in Mammals and Implications for Stable Isotope Analysis for Diet and Climate Signals

University Of Utah, Salt Lake City UT

Investigators

Abstract

The focus of this project is to study how temporal changes in the isotopic composition of mammals are recorded in developing tooth enamel. Teeth form progressively from crown to root and act as recorders of seasonal isotopic variation in the animal blood bicarbonate reservoir. This variation is in turn related to seasonal variations in climate, food availability, migration, ecosystem interactions, and other environmental conditions. Isotopic signals are preserved in fossil tooth enamel, so teeth are important archives of ancient seasonality and environmental variation on short time scales. Despite the wide usage of intra-tooth isotope approaches, there is considerable uncertainty as to how the measured signals relate to actual signals of variation within the animal reservoir. This uncertainty stems from inadequate knowledge of the temporal and spatial patterns of enamel mineral deposition and accumulation in teeth that are commonly studied. Although promising, the intra-tooth isotope method will remain compromised as a paleoindicator until these uncertainties are addressed. We will use micro-computed tomography (microCT) to investigate the temporal and spatial pattern of enamel mineral accumulation in developing teeth of animals of various ages from a range of species. Maturation parameters determined from the microCT data will enable development of tooth- and species-specific models that describe how primary input signals are recorded as intra-tooth isotopic profiles. Inverse models will be developed that allow estimates of primary input signals based on measured isotope data and knowledge of maturation parameters. Comparison between model results and known isotopic changes in the animals studied will allow direct evaluation of the accuracy of these models. Specifically, this study will provide maturation parameters for dentitions of Alpaca (alpaca), Capra (goat), and Bos (cow). These animals underwent strictly controlled isotopic changes during tooth formation, and therefore this study will show the extent to which forward and inverse models based on maturation parameters allow for reconstruction of primary input signals. These species span a range of diversity within the artiodactyla and will show whether general models can be applied to many species within this order. Intellectual merit. This study will significantly increase the understanding of a basic tool used by a wide variety of researchers. The microCT, forward modeling, and inversion modeling methods will be of immediate use to researchers using the intra-tooth isotope method. Forward and inverse modeling learned by other researchers as a result of this study will broaden scientific background and benefit future studies. Advances in the intra-tooth method owing to this study will help advance our understanding of ancient human environments and cultures, behavior and ecosystem context of extinct species, and ancient climates and environments. Broader impact. This research will form the Ph.D dissertation of Benjamin Passey. He will be responsible for the design, execution, and dissemination of this research and will learn valuable skills in project management, laboratory practice, data evaluation, and professional communication. An undergraduate student will be involved in laboratory aspects of this project. This person will gain invaluable first-hand research experience and have opportunities to attend professional meetings to present results