Northern fur seals are extremely sexually dimorphic. Male and female northern fur seals vary both in size and color. Adult females are smaller than males, measuring about 142 cm and weighing 43-50 kg, and are usually gray or brown. Adult males tend to be reddish in coloration or black, measure 213 cm, and weigh between 181 and 272 kg. Northern fur seal pups have black pelage. Additional characteristics include vibrissae, which are white on the adult and black on the pup. Pups usually have lighter markings on the nose and underside. Adults, especially males, have a mane, which is similar to the mantle of some squirrels. The adults have small noses, thick underfur,and long pinnae. The fur on the front flippers stops at the wrist.
Range mass: 43 to 272 kg.
Average mass: 147.50 kg.
Average length: 142-213 cm.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: male larger; sexes colored or patterned differently; ornamentation