Densest fur

The sea otter (Enhydra lutris) has the densest fur of any mammal, with around 100,000–160,000 hairs per square centimetre (650,000–1.03 million hairs per square inch), though in some areas this dips to 26,000 hairs per square centimetre (168,000 hairs per square inch). The world's sea otter population is found in colonies in the north-east Pacific, off eastern Russia, western Canada and western USA – particularly off the coast of Alaska, USA.

Unlike other marine mammals, they do not have a layer of blubber to keep them warm. Instead, they rely on this dense, water-resistant fur and an increased metabolism to trap and generate warmth, particularly during feeding dives in which sea otters can reach depths of 75 m (246 ft).

The fur varies in density across different parts of the body; for instance, on the legs and cheeks, it's at the thinner end of the range, while on the rump and sides, it's at its thickest.

Sea otters are also among the smallest marine mammals.