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.