Lemur Diversification

My dissertation work focused on the ecomorphology of lemur teeth and what reconstructions of ancestral tooth shapes might reveal about the evolutionary history of lemurs. I used a class of measurements called dental topography metrics, which mathematically characterize the functional properties of tooth surfaces. Working with colleagues at Duke, I found the combinations of metrics that were best able to distinguish lemurs by dietary ecology, including folivores from insectivores, which has traditionally proven difficult. Leaves and insect tissues are both high in toughness, but the material properties of leaves may be less important than their fundamentally planar geometries. This appears to select for the elaboration of elongated cutting blades and relatively flat basins, driving high variability in tooth curvature (measured as a high coefficient of variation of Dirichlet normal energy). This observation was supported by a second study that tests for relationships between lemur community dental topography values and precipitation and precipitation seasonality at sites across Madagascar. I found that adaptations for processing leaves were not strongly related to their climatically inferred material properties, but instead to the likely importance of leaves in the diet of lemur communities.

We used these effective combinations of metrics to reconstruct dietary adaptation in extinct lemurs and applied phylogenetic modeling approaches to test for an adaptive radiation of lemur dietary strategies in the deep past. We combined ancestral state reconstructions of dental topography metrics with a novel approach to reconstructing continuous tooth shape across the evolutionary history of strepsirrhines and found that the spread of forests on Madagascar coincided with an expansion of lemur ecospace occupation apparently related to the exploitation of defended plant resources, including leaves.

Eocene Primates

The North American primate fauna of the Eocene represent an excellent system in which to observe the dynamics of morphological diversification and decline in response to climatic trends across a thirty-million-year interval. I am working to combine body mass estimates with the dental topography metrics calculated on molars scanned from North American fossil primates in order to measure the relationships between morphological disparity, temperature, and other climate factors. If climatic amelioration was associated with the opening of ecological opportunity for fossil primates, these niches likely contracted as climates cooled toward the Oligocene, and disparity should show a strong correlation with temperature. Alternately, if cooling drove diverging specialization, then this should be reflected in a negative correlation between temperature and disparity.

Tooth wear

My previous work, like most studies of dental topography, has focused on unworn tooth shape. However, tooth surface morphology changes over the lifespan of an individual as the enamel crown erodes and dentine is exposed. It is thought that certain dental morphologies may have evolved to best maintain functional shape across a wear sequence. Studying this adaptation provides the potential opportunity to observe the refinement of a functionally selective character across the evolution of a lineage. This requires a group of mammals that seem to have acquired a unique dental morphology related to the maintenance of functional shape across a wear gradient. Tapriomorph perissodactyls may represent just such a lineage, as the modern tapirid members evolved a distinctive, bilophodont tooth morphology from more generalized, bunodont ancestors. As a first step, I have begun to work with faculty from the Center of Excellence in Paleontology at East Tennessee State University to analyze change in functional shape across a wear sequence in the abundant fossil tapirs of the Gray Fossil Site. Future work will examine functional shape change across wear sequences in earlier fossil tapiromorphs.