Date Approved

6-24-2025

Graduate Degree Type

Thesis

Degree Name

Health Sciences (M.H.S.)

Degree Program

Biomedical Sciences

First Advisor

Dr. Laura Stroik

Second Advisor

Dr. Natalie Laudicina

Third Advisor

Dr. Tara Kneeshaw

Academic Year

2024/2025

Abstract

Molar anatomy reflects the functional demands of food mastication, and dental topography provides a quantitative method for evaluating how molar structure relates to dietary niche. Relief index (RFI), a dental topographic measure, has been successfully used to infer diet in extant and fossil mammals. This study tests two hypotheses regarding mandibular molars of early Eocene omomyids: (1) There is an association between changes in omomyid RFI values of first and second mandibular molars and changes in climatic variables (temperature and precipitation) from Wa0 to Wa5, and (2) The first and second mandibular molar RFI values of omomyid species are significantly different from one another.

RFI was calculated from 130 micro-CT scanned first and second mandibular molars representing 17 omomyid species from the Bighorn Basin, Wyoming. Climatic variables were represented by d18O (temperature) and d13C (precipitation) values from Zachos et al. (2001). Because data were non-normal, non-parametric statistical tests were used. For hypothesis 1, Spearman’s rank analysis indicated no significant correlation between RFI and either d18O (ρ = –0.100, p = 0.873) or d13C (ρ = –0.500, p = 0.391). A Kruskal-Wallis test did not detect significant differences in RFI across sub-NALMAs (p = 0.092), but Dunn’s post hoc comparisons identified several potentially meaningful shifts over time. In contrast, both d18O and d13C exhibited significant variation across sub-NALMAs ( p < 0.001 for both), confirming significant changes in climate during the study interval.

For hypothesis 2, Kruskal-Wallis test revealed no significant difference in RFI values among omomyids (p = 0.237), but 32 out of 406 pairwise comparisons were significant prior to Bonferroni correction. Some species showed temporal shifts in RFI, and others displayed overlapping values within the same dietary category. Dietary categories (omnivore and insectivore) were assigned based on RFI thresholds from extant primates, and the degree of overlap suggests that many species may have experienced dietary niche competition. These findings suggest that while climate was not significantly associated with RFI, interspecific interactions may have contributed to changes in molar anatomy. This study supports the use of RFI in reconstructing dietary patterns, contributing to the understanding of primate evolution.

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