[MARMAM] Radiation of extant cetaceans driven by restructuring of the oceans

ewan fordyce ewan.fordyce at stonebow.otago.ac.nz
Thu Oct 8 12:05:32 PDT 2009

This new article -
Steeman, M.E. et al., 2009, Radiation of Extant Cetaceans Driven by 
Restructuring of the Oceans (Systematic Zoology, 
is currently available via open access at 

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 for 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 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 2 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. [Cetacea; evolution; 
molecular phylogeny; palaeo-ocean restructuring; speciation.]

R. Ewan Fordyce
*Associate Professor, and Head of Department,
Department of Geology University of Otago, PO Box 56, Dunedin 9054, NZ
web: http://www.otago.ac.nz/geology/people/fordyce/index.html
*Research Associate, National Museum of Natural History, Smithsonian 

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