Colonization of the Southern Hemisphere by fur seals and sea lions (Carnivora: Otariidae) revealed by combined evidence phylogenetic and Bayesian biogeographical analysis

Fur seals and sea lions (Carnivora: Otariidae) evolved in the North Pacific and later dispersed throughout the Southern Hemisphere. However, the timing and number of dispersals into the Southern Hemisphere still remain poorly understood. To determine the biogeographical patterns of dispersal within fur seals and sea lions, we conducted cladistic analyses using combined evidence incorporating morphological and molecular data. The phylogeny produced in this study was then incorporated into Bayesian biogeographical analyses to reconstruct ancestral points of origin and dispersal patterns for otariid clades. Combined evidence analyses supported Callorhinus as the earliest diverging extant otariid, and a strongly supported northern sea lion clade (Zalophus, Eumetopias, and Proterozetes) as the sister group to a southern clade comprising the remainder of Otariidae. Fossil data constrained the timing and location of this dispersal as occurring between 6 and 7 Mya during a period of unusually cool sea surface temperatures and high productivity in the eastern equatorial Pacific, far older than suggested by prior studies. Our study indicates that the distribution of fur seals and sea lions is tightly linked to sea surface temperature and productivity, and suggests that otariids may be vulnerable to future anthropogenic climate change.