Cenozoic climate change and the evolution of North American mammalian predator ecomorphology

Abstract: The trend of global cooling across the Cenozoic transformed the North American landscape from closed forest to more open grasslands, resulting in dietary adaptations in herbivores in response to shifting resources. In contrast, the material properties of the predator food source (muscle, skin, and bone) have remained constant over this transition, suggesting a corresponding lack of change in predator dietary adaptations. We investigated the North American mammalian predator fossil record using a tooth-shape metric and body mass, predicting that the former would exhibit stability. Instead, we found that mean molar morphology became more blade-like, with our tooth-shape metric sharply increasing in the late Eocene and remaining high from the Oligocene onward. Subsequent tests in extant carnivorans reveal taxa with more bladelike teeth are prevalent in more open environments. Our results reveal an unexpected functional shift among North American predators in response to large-scale environmental changes across the Cenozoic

Using morphological variation of the skull to understand evolutionary trends across taxonomic scales in Carnivora

Carnivorans are historically well-studied because of their extensive fossil record in North America and their great morphological and ecological diversity. To understand evolutionary trends with carnivorans, it is useful to turn to features of the skull and teeth, which are documented proxies for broader ecological categories such as body mass and diet. For example, the correlation between the lower first molar length and body mass is well documented. Other features of carnivoran skulls remain unexplored in terms of the types of variation present and the functional implications of that variation. For example, domestic dogs exist in a distinct morphological space given the intense artificial selection they have undergone. Therefore, I used the carnivoran skull to ask questions about the variation and evolutionary plasticity of certain features, the functional implications of this variation, and how carnivorans have shifted across different functional categories over time. In Chapter 1 I studied the variation of the 3D shape of the cribriform plate in domestic dogs, as it is closely associated with the olfactory nerves and found its shape varies with the dramatic changes in skull shape across domestic dog breeds. In Chapter 2 I quantified dental variation in domestic dogs as a model of how variability in tooth shape and number is generated under conditions of minimal selection pressure and compared that variation to other canid species and found that there is greater variation across a suite of dental features in domestic dogs when compared to Canidae more broadly. In Chapter 3 I used dental measurements to estimate body mass and diet for North American fossil carnivoran species over the past 40 million years to analyze trends and shifts in the distribution of species across these categories and compared these shifts to climatic events and taxonomic turnover. I found that carnivorans have moved through distinct ecological regimes and that diet diversifies before body mass