Dental Ecometrics as a Proxy of Paleoenvironment Reconstruction in the Miocene of South America
In this dissertation I compile modern mammalian faunal lists, as well as ecomorphological measurements on living marsupials and rodents, to relate the diversity of small mammals, specifically the distributions of their dental topographies, to the climates in which they are found. The emphasis of this dissertation is to demonstrate the potential of distributions of dental topography metrics as proxies for the reconstruction of paleoenvironments in the Miocene of South America.
In Chapter 2, I compile complete, non-volant mammalian species lists for 85 localities across South America as well as 17 localities across Australia and New Guinea. Climatic and habitat variables were also recorded at each locality using GIS spatial data. Additionally, basic ecological data was collected for each species, including: diet, body size, and mode of locomotion. Niche indices that describe the relative numbers of different ecologies were calculated for each locality. These indices then served as the predictor values in a handful of regression models, including regression trees, random forests, and Gaussian process regression. The Australian/New Guinean localities were used as a geographically and phylogenetically independent for the purposes of testing the models derived from South America.
As for the dental ecomorphological analysis, I use three separate measures of dental topography, each of which measures a different component of dental topography; relief (the Relief Index, or RFI), complexity (orientation patch count rotated, OPCR), and sharpness (Dirichlet normal energy, DNE). Together, these metrics quantify the shape of the tooth surface without regard for tooth size. They also do not depend on homologous features on the tooth surface for comparative analysis, allowing a broad taxonomic sample as I present here. After a methodological study of DNE in Chapter 3, I present correlative studies of dental topography and dietary ecology in marsupials and rodents in Chapters 4 and 5, respectively. Finally, using the same localities from Chapter 2, I analyze the distributions of dental topography metrics as they relate to climate and habitat.
Results suggest that sharpness and relief are positively correlated with a higher amount of tough foods—such as leaves or insects—in the diet of marsupials, and that relief is positively correlated with grass-eating in rodents. The distributions of all three metrics show some utility when used as a proxy for climatic variables, though the distributions of RFI in marsupials and OPCR in rodents demonstrate the best correlations.
Overall, this dissertation suggests that dental topography can be used to discriminate dietary categories in a wide variety of mammalian groups, and that the distributions of dental ecometrics can be used as proxies for paleoenvironment reconstruction. This may eliminate the need to reconstruct behavior in individual taxa in order to construct ecological indices for fossil mammalian communities, thus offering a more direct avenue to reconstructing past environments.
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