Seals range in size from the 1 m and 45 kg Baikal seal to the 5 m and 3,200 kg southern elephant seal which is also the largest carnivoran. They have streamlined bodies and four limbs that are modified into flippers. Though not as fast in the water as dolphins seals are more flexible and agile. Otariids use their front limbs primarily to propel themselves through the water while phocids and walruses use their hind limbs. Otariids and walruses have hind limbs that can be pulled under the body and used as legs on land. By comparison terrestrial locomotion by phocids is more cumbersome. Otariids have visible external ears while phocids and walruses lack these. Pinnipeds have well-developed senses their eyesight and hearing are adapted for both air and water and they have an advanced tactile system in their whiskers or vibrissae. Some species are well adapted for diving to great depths. They have a layer of fat or blubber under the skin to keep warm in the cold water and other than the walrus all species are covered in fur.