Chapter 3

Abstract

Previous hypotheses for the origin and diversification of pinnipeds have followed a narrative approach based mostly on dispersalist (i.e., center of origin) explanations. Using an analytical approach, we present a testable hypothesis to explain the evolutionary biogeography of pinnipedimorphs (fur seals, sea lions, walruses, seals, and their fossil relatives) based on both dispersal and vicariant events in the context of a species-level phylogenetic framework. This integrated hypothesis considers many lines of evidence, including physical and ecologic factors controlling modern pinniped distributions, past geologic events related to opening and closing of seaways, paleoceanographic models, the improving pinniped fossil record, and pinniped phylogenetic analyses based on both morphologic and molecular data sets. Oceanic biogeographic regions and faunal provinces are defined and oceanic circulation patterns discussed with reference to the distribution of extant and fossil species. Paleobiogeographic hypotheses for each of the major pinniped lineages are presented using area cladograms and paleogeographic maps showing oceanographic and tectonic changes during successive intervals of the Cenozoic.