Recent genetic evidence suggests that there may in fact be three different species instead of a single Orcinus orca. These three species correspond to ecotypes, which had already been recognized as having differences in size and color pattern, behavior, prey preference, and social organization.
Researchers sequenced mitochondrial genomes of 143 orcas and three outgroup species (false killer whale, long-finned pilot whale and short-finned pilot whale). They found 66 orca hapolotypes which clustered geographically and by ecotype. They estimate that the clades diverged between 150,000 and 700,000 years ago, with two Pacific clades splitting first and then an Atlantic clade more recently.
- Mitochondrial DNA Points to Multiple Killer Whale Species. GenomeWeb Daily News. 23 April 2010. http://www.genomeweb.com/node/939227
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