Polar Bear (Ursus maritimus)

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A bear that is legally and ecologically a marine mammal: it hunts seals from the surface of the sea ice, and where the ice goes it goes. It is the clearest single expression of the Arctic's structure, because it could only exist where a land carnivore lineage had physical access to a frozen ocean - it diverged from brown bears comparatively recently and walked out onto the sea from a continent. The IUCN assessment published in 2015 gave a global figure in the region of twenty-six thousand animals across nineteen recognised subpopulations, with wide uncertainty and several subpopulations for which no reliable estimate exists at all, and listed the species as Vulnerable with sea-ice loss as the principal threat. Nothing in Antarctica occupies this niche, and nothing can: there is no land route to the southern ice.