On the northern tip of New Zealand's South Island, bottlenose dolphins (Tursiops truncatus) occasionally pass through Admiralty Bay in large, fast-traveling groups of 100 or so individuals. Watching such a group race and splash through the water is reminiscent of a stampeding herd of ungulates, cetaceans' closest terrestrial ancestors. At other times, smaller social groups of bottlenose dolphins appear in the bay and provide a glimpse of the behavioral complexity that dolphins share with their distant relatives, the primates (Fig. 1). Despite being evolutionarily separated for 95 million years and evolving in vastly different environments, cetaceans and primates share striking similarities in behavior, socioecological problem-solving, life-history patterns, and cognitive capacity. By comparing attributes shared by primates and cetaceans, distraction from phylogenetic "noise" is minimized and our understanding of evolutionary pathways is enhanced. In particular, cetaceans provide a powerful outgroup for studying the evolution of primate social organization.
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