| Pinnipeds (seals, sea lions, and walruses) are the second most diverse clade of marine mammals alive today (∼36 species). Improved understanding of pinniped evolution may allow us to identify important drivers and constraints towards adaptation to marine environments. The purpose of this project was to explore the evolution and ecology of fossil pinnipeds using morphology within the context of a revised phylogeny for the group. Two morphological proxies were examined; body size and tooth morphology. Body size is poorly known for many fossil pinnipeds, particularly those that are known only from fragmentary fossil material. A database of extant pinniped measurements was used to create linear multivariate regression equations for the estimation of body size in fossil pinnipeds. This data was then used to reconstruct the evolution of body size in pinnipeds and I determined there was no trend toward increasing body size (Cope's rule), and that body size change in pinnipeds related to diversification away from a minimum body size threshold, associated with increased Middle Miocene productivity. I also performed principal components and cluster analysis to examine variation in tooth spacing and size in Pinnipedia, and found that differences in tooth morphology correlated with importance of teeth in feeding; taxa which used their teeth for filtration of food or biting prey had larger, more closely spaced teeth than those species which used suction feeding or fed on small prey items that could be swallowed whole. I was able to use this data to infer the feeding ecology of the basal pinnipedimorph Enaliarctos, and determined that despite similarities with terrestrial carnivores, Enaliarctos was a pierce feeder that did not perform mastication. To improve reconstruction of changes in body size and tooth morphology for pinnipeds, I also performed a combined evidence phylogenetic analysis on the Otariidae, a clade whose evolution is still poorly understood compared to other pinniped families. This phylogeny was then used to interpret the biogeographic history of the group, identifying a single early southward dispersal from the North Pacific followed by subsequent diversification 6--7 Myr in the South Pacific. |
