@ARTICLE{TreeBASE2Ref18615, author = {M. E. Steeman and Martin Bay Hebsgaard and R. Ewan Fordyce and Simon Ho and D. L. Rabosky and Rasmus Nielsen and Carsten Rahbek and Henrik Glenner and Martin V S?rensen and Eske Willerslev}, title = {Radiation of Extant Cetaceans Driven by Restructuring of the Oceans}, year = {2009}, keywords = {}, doi = {10.1093/sysbio/syp060}, url = {}, pmid = {}, journal = {Systematic Biology}, volume = {58}, number = {6}, pages = {573--585}, abstract = {The remarkable fossil record of whales and dolphins (Cetacea) has made them an exemplar of macroevolution. Although their overall adaptive transition from terrestrial to fully aquatic organisms is well known, this is not true of the radiation of modern whales. Here, we explore the diversification of extant cetaceans by constructing a robust molecular phylogeny that includes 87 of 89 extant species. The phylogeny and divergence times are derived from nuclear and mitochondrial markers, calibrated with fossils. We find that the toothed whales are monophyletic, suggesting that echolocation evolved only once early in that lineage some 36-34 million years ago (Ma). The rorqual family (Balaenopteridae) is restored with the exclusion of the gray whale, suggesting that gulp-feeding evolved 18-16 Ma. Delphinida, comprising all living dolphins and porpoises other than the Ganges/Indus dolphins, originated about 26 Ma; it contains the taxonomically rich delphinids, which began diversifying less than 11 Ma. We tested two hypothesized drivers of the extant cetacean radiation by assessing the tempo of lineage accumulation through time. We find no support for a rapid burst of speciation early in the history of extant whales, contrasting with expectations of an adaptive-radiation model. However, we do find support for increased diversification rates during periods of pronounced physical restructuring of the oceans. The results imply that paleogeographic and paleoceanographic changes, such as closure of major seaways, have influenced the dynamics of radiation in extant cetaceans.} }

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