Doctoral Dissertation Improvement Grant: Experimental Determination of Tooth Mineralization Patterns in Ungulates for Application to Paleoseasonality Reconstruction

Harvard University, Cambridge MA

Investigators

Abstract

Scholars have been debating the conditions that led to the evolution of humans' large brains and unique behaviors, including complex stone tool use and language, for more than a century. One influential theory proposes that these features emerged in response to seasonal resource availability in Africa over the last five million years. Geological and paleontological data suggest that changing rainfall patterns might have produced more arid African ecosystems and novel foraging behaviors, although approaches for documenting ancient precipitation patterns remain rudimentary. Under the direction of Dr. Tanya Smith, Daniel Green aims to improve methods of seasonal reconstruction with new laboratory techniques and experimentation, facilitating research on ancient climate change during key periods in human evolution. Climatic patterns may be reconstructed through chemical analysis of teeth, which record environmental chemistry during formation and remain unchanged after death and fossilization. Tooth increments, analogous to rings in trees, form every day during childhood from ingested minerals that are in equilibrium with local water sources. As seasons pass, the composition of isotopes (atomic variants) change, and teeth record these changes. Importantly, isotopes in teeth record seasonal changes that can be related to time markers, facilitating precise estimates of environmental change. This project will improve climate reconstruction by precisely mapping the geometry and timing of tooth mineralization. A combination of cutting-edge synchrotron imaging and scanning electron microscopy of developing sheep teeth will yield mineral density change over time. This project then tests these results using animals subject to an isotopic water switch, experimentally demonstrating the relationship between tooth chemistry and changes in water that approximates seasonal variation. Ultimately, a concrete understanding of how environmentally sensitive minerals are added to teeth will improve seasonal reconstruction, and will allow one to investigate if marked climatic change accompanied the development of unique human anatomy and behaviors. This project will train graduate and undergraduate students, and enhance collaborations with scholars in Europe and Africa. Results of this research will be broadly disseminated in professional journals and meetings, and presented to public audiences.