Doctoral Dissertation Improvement: Incremental Development of Primate Enamel

Suny At Stony Brook, Stony Brook NY

Investigators

Abstract

Dental remains are the most common, well-preserved type of fossil evidence for extinct species of primates. Many researchers have studied aspects of tooth shape, wear, and developmental timing in an attempt to understand the evolution of humans and their closest relatives. Teeth are made up of several hard tissues: enamel, dentine, and cementum. One recent area of research is based on enamel microstructure, which is the internal microscopic structure of a tooth crown. Enamel forms in an incremental manner similar to the growth pattern of tree rings, regular lines that record the number of years a tree has been growing. During tooth growth, a series of near-weekly and daily lines are formed that record the position of the developing front and the daily growth of the enamel-forming cells. Counts and measurements of these features provide information on the rate, pattern, and total time required to form the tooth crown. The first aim of this study is to refine our current understanding of enamel development by establishing the periodicity, or frequency, of incremental features in a large sample of newborn and juvenile pigtailed macaques. This will be accomplished by relating these incremental features to known interval fluorescent labels, which were injected during a previous study of bone growth. The growth lines will be counted between specific labels, which will allow us to determine how much time it takes to form each type of feature. The second aim of this study is to document the degree of variation of these features in orangutan and chimpanzee dentitions. Comparisons of incremental features will be made among individuals, between subspecies of orangutans, and between chimpanzees and orangutans. This project will provide additional support for studies of tooth growth by allowing standard methods to be tested, and will allow better assessment of results based on small sample sizes. Information collected on tooth growth in chimpanzees and orangutans will also serve as the largest comparative sample for the interpretation of fossil material. Ultimately, these results may allow researchers to better understand the relationships between humans and our closest relatives, including living and fossil apes.