Orcas or killer whales have a cosmopolitan distribution and several distinct populations or types have been documented or suggested. Three to five types of orcas may be distinct enough to be considered different races, subspecies, or possibly even species (see species problem). The IUCN reported in 2008, "The taxonomy of this genus is clearly in need of review, and it is likely that O. orca will be split into a number of different species or at least subspecies over the next few years." However, large variation in the ecological distinctiveness of different orca groups complicate simple differentiation into types. Mammal-eating orcas in different regions were long thought likely to be closely related, but genetic testing has refuted this hypothesis.
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Transient orca in the context of Cosmopolitan distribution
In biogeography, a cosmopolitan distribution is the range of a taxon that extends across most or all of the surface of the Earth, in appropriate habitats; most cosmopolitan species are known to be highly adaptable to a range of climatic and environmental conditions, though this is not always so. Killer whales (orcas) are among the most well-known cosmopolitan species on the planet, as they maintain several different resident and transient populations in every major oceanic body on Earth, from the Arctic Circle to Antarctica and every coastal and open-water region in-between. Such a taxon (usually a species) is said to have a cosmopolitan distribution, or exhibit cosmopolitanism, as a species; another example, the rock dove (commonly referred to as a 'pigeon'), in addition to having been bred domestically for centuries, now occurs in most urban areas around the world.
The extreme opposite of a cosmopolitan species is an endemic (native) species, or one found only in a single geographical location. Endemism usually results in organisms with specific adaptations to one particular climate or region, and the species would likely face challenges if placed in a different environment. There are far more examples of endemic species than cosmopolitan species; one example being the snow leopard, a species found only in Central Asian mountain ranges, an environment to which the cats have adapted over millions of years.