Master's Theses

Document Type

Thesis

Date of Award

Summer 2016

Degree Name

Master of Science (MS)

Department

Geosciences

Advisor

Dr. Laura Wilson

Abstract

Dental microwear analysis is the study of microscopic features on the surfaces of teeth, and is used to reconstruct and analyze diet in extinct and extant animals. Microwear analysis on ungulates is typically conducted on the paracone or protoconid of the second molar, as these cusps are usually the first point of contact between upper and lower teeth during the chewing stroke. However, the exact method of mastication varies in different groups of ungulates, and the influence of mastication on the location and production of microwear features has been studied very little. Additionally, the role of highly specialized enamel microstructure in the production of microwear features has not been examined in many groups of animals. The goal of this project is to analyze central tendency of microwear features among cusps and between chewing facets in order to determine if a single cusp or facet type is more reliable for interpretation than other cusps or facet types in the North American Miocene rhinoceros, Teleoceras fossiger. This is accomplished through the testing of three main hypotheses. First, it is predicted that cusps that collide more frequently with other cusps will have higher numbers of microwear features than cusps that interact less frequently. Second, it is predicted that Phase 1 chewing facets will have more pits than Phase 2 facets, and Phase 2 facets will have more scratches than Phase 1 facets. Third, it is predicted that cusps constructed of normal, soft enamel will have a higher total number of features than cusps constructed of highly resistant enamel. The lower second molars of 11 T. fossiger specimens were selected for analysis, as numerous complete dentaries were available for study. A total of 31 cusps from the 11 teeth were cleaned, prepared, and sampled in order to capture potential variation produced during the chewing stroke. Cusps were identified as Phase 1 or Phase 2 chewing facets, with each Phase associated with either normal enamel or enamel with specialized, resistant Hunter-Schreger Bands. Using low magnification microwear techniques, pits and scratches were identified and counted on all cusps and facets using 0.4 mm2 areas, and the data were analyzed in R 3.1.1. When testing the first hypothesis, eleven paired t-tests and one Wilcoxon paired sample test resulted in a single significant comparison between the hypoconid and the protoconid, with the hypoconid having significantly higher numbers of scratches than the protoconid. When testing the second hypothesis, a paired t-test and a Wilcoxon paired sample test comparing the number of scratches and pits between Phase types did not produce significant values. Finally, when testing the third hypothesis, a paired t-test comparing the total number of features between Phase types indicated no significant differences. Comparison of the characteristics of the hypoconid to other cusps indicates that mastication and enamel microstructure work in combination to preferentially produce more scratches on the hypoconid than on other cusps in T. fossiger, partially supporting the first hypothesis and the third hypothesis. Consequently, it is recommended that the hypoconid is not used for dietary analysis due to its higher variability in the number of scratches, which will affect the results of dietary reconstruction studies on T. fossiger.

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© 2016 Kelsie Abrams

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